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Examining approaches to
investigating the United Kingdom’s
existing building fabric in the
pursuit of net zero targets
Ebere Donatus Okonta and Farzad Rahimian
School of Computing, Engineering and Digital Technologies,
Teesside University, Middlesbrough, UK
Abstract
Purpose –The purpose of this study is to investigate and analyse the potential of existing buildings in the
UK to contribute to the net-zero emissions target. Specifically, it aims to address the significant emissions
from building fabricswhich pose a threat to achieving these targets if notproperly addressed.
Design/methodology/approach –The study, based on a literature review and ten (10) case studies,
explored five investigative approaches for evaluating building fabric: thermal imaging, in situ U-value
testing, airtightness testing, energy assessment and condensation risk analysis. Cross-case analysis was used
to evaluate both case studiesusing each approach. These methodologies were pivotal in assessing buildings’
existing condition andenergy consumption and contributing tothe UK’s net-zero ambitions.
Findings –Findings reveal that incorporating the earlier approaches into the building fabric showed great
benefits. Significant temperature regulation issues were identified, energy consumption decreased by 15%
after improvements, poor insulation and artistry quality affected the U-values of buildings. Implementing
retrofits such as solar panels, air vents, insulation, heat recovery and air-sourced heat pumps significantly
improved thermal performance while reducing energy consumption. Pulse technology proved effective in
measuring airtightness, even in extremely airtight houses, and high airflow and moisture management were
essential in preserving historic building fabric.
Originality/value –The research stresses the need to understand investigative approaches’strengths,
limitations and synergies for cost-effective energy performance strategies. It emphasizes the urgency of eliminating
carbon dioxide (CO
2
) and greenhouse gas emissions to combat global warming and meet the 1.5° C threshold.
Keywords Net zero, Building fabric, Energy efficiency, Retrofitting approaches, Existing buildings
Paper type Case study
1. Introduction
“Net Zero”means reducing greenhouse gas emissions to zero if possible or a point comparable
to zero where remnants of emissions can be successfully absorbed by the natural environment
without harm (United Nations, 2021). According to Reall (2021),theraceto“Zero”aims for a
vital, resilient and decarbonised planet, building momentum against future hazards for
sustainable development. With a focus on balance, net zero emissions entail achieving balance
© Ebere Donatus Okonta and Farzad Rahimian. Published by Emerald Publishing Limited. This
article is published under the Creative Commons Attribution (CC BY 4.0) licence. Anyone may
reproduce, distribute, translate and create derivative works of this article (for both commercial and
non-commercial purposes), subject to full attribution to the original publication and authors. The full
terms of this licence may be seen at http://creativecommons.org/licences/by/4.0/legalcode
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Received30 September 2023
Revised 2 November2023
29 December 2023
17 February 2024
11 March 2024
13 April 2024
Accepted 29 May 2024
Urbanization, Sustainability and
Society
Vol. 1 No. 1, 2024
pp. 78-114
Emerald Publishing Limited
2976-8993
DOI 10.1108/USS-09-2023-0004
The current issue and full text archive of this journal is available on Emerald Insight at:
https://www.emerald.com/insight/2976-8993.htm
and equilibrium between greenhouse gas (GHG) emissions released into the atmosphere and
those expelled out of the atmosphere (Climate Council, 2021). The major greenhouse gases tied
to the cause of global warming and climate change include carbon dioxide (CO
2
), methane
(CH
4
), nitrous oxide (N
2
O), hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride
(SF
6
)(United Nations Environment Programme, 2022). The CO
2
is the major contributor to
climate change (IEA, 2021a). The global net-zero targets focus on reducing energy-related CO
2
emissions to zero by 2050 and providing an opportunity to limit global temperature rise by
1.5°C (IEA, 2021b, p. 1). The UK (UK) has taken steps uniquely to pursue a net zero goal. This
effort is reflected in the 10-point strategy for a green industrial revolution outlined by the HM
government in 2020 (HM government, 2020). This strategy involves enhancing offshore wind
capabilities, boosting the production of low-carbon hydrogen, expanding the utilization of
nuclear energy, shifting towards emission-free transportation, improving eco-friendly public
transit, striving for aviation and maritime emission neutrality, promoting sustainable
infrastructure, deploying carbon capture and storage, conserving natural ecosystems and
biodiversity and advancing environmentally responsible financial practices (HM government,
2020). GHG emissions among UK residents increased by 6% to over 505 million tonnes of CO
2
equivalent between 2020 and 2021, and CO
2
comprises 85% of GHG emissions in the UK, with
methane (CH4) closely following greenhouse gas emissions (Office for National Statistics,
2022). Consumer expenditure stands as the largest individual contributor to emissions in the
UK, constituting 27%, while electricity, gas, steam, air conditioning, manufacturing and
transportation collectively account for 72% of emissions in 2021 (Office for National Statistics,
2022). The UK has thus far expanded its gross domestic product by 75% while reducing
emission levels by 43%, becoming the first major economy in 2019 to adopt a legally binding
commitment to achieve net zero greenhouse gas emissions by 2050 (Jones and Tam, 2023). In
the UK built environment, including residential and commercial buildings, 77% are
residential, 14% are commercial and 10% are public sector assets (Committee on Climate
Change, 2018). The UK’s Environmental Audit Committee has highlighted that government
policies have not provided sufficient momentum to address emissions reduction in this sector
(UK Parliament, 2022). Space heating is one of the most polluting activities associated with the
construction industry, accounting for 25% of total energy consumption in the UK (Committee
on Climate Change, 2019). Further emissions from the building industry are caused by using
grid electricity to power residences. In 2017, the UK construction industry accounted for 66%
of total national power usage (Committee on Climate Change, 2018).
Most of the buildings that will be used in 2050 and 2070 to achieve the net zero target
already exist (Dönmezçelik et al.,2023). In 2050, every existing building stock must be
converted to almost zero-energy structures according to the European Union Energy
Performance of Buildings Directive (European Union Law, 2018). Innovations that raise the
affordability of integrating energy efficiency into newly constructed homes and enable
retrofitting of existing properties to high energy efficiency standards will be necessary to
meet these aims. This allows energy storage materials to be built into new construction
properties and incorporated into modules/materials for retrofitting existing buildings.
Supporting the integration of renewable energy-generating advances into new and existing
properties (HM Government, 2018).
The study emphasizes the importance of investigating the existing building fabric;
however, there is a research gap in the long-term performance monitoring of retrofitted
buildings. A comprehensive understanding of the energy savings and carbon reductions
achieved through different approaches is essential to validate retrofit interventions’
effectiveness and identify improvement areas (Crilly et al.,2012;Prabatha et al.,2020;
Okonta, 2023). The study provides an overview of the approaches used to investigate the
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UK’s existing building fabric in the pursuit of net zero goals, including thermal imaging, in
situ U-value testing, air tightness testing, energy assessment, condensation risk analysis
and insulation assessment, and will seek to pursue these objectives:
To provide insights and recommendations for building owners, energy professionals
and policymakers on effectively implementing these approaches to drive successful
retrofit interventions;
To contribute to the body of knowledge on investigating the existing building fabric
in the context of net zero targets, specifically focusing on the UK’s built environment;
and
To support the UK’s efforts in achieving its net zero goals by providing evidence-
based insights into effective approaches for transforming existing buildings’thermal
performance and energy efficiency.
This study uses a three-stage methodology to investigate the energy efficiency of the UK’s
existing building fabric. First, a comprehensive literature review establishes the groundwork.
Second, diverse case studies are selected to represent various investigative methodologies,
covering thermal imaging, in situ U-value testing, airtightness testing, energy assessment
and condensation risk analysis. Third, a case study analysis is conducted to provide real-
world insights, and a cross-case analysis compares and contrasts two case studies within
each investigative approach. This approach bridges theory with practical solutions for
transforming the UK’s building fabric towards net-zero goals.
2. Retrofitting buildings
Retrofitting a building is a contemporary technique used to improve the reliability of a
structure by improving its safety, durability and applicability with additional attributes and
technology to the structure (Machhi, 2022). In much simpler terms, retrofitting a building
entails modifying an existing structure to a new and stable one that could stand against or
constitute a hazard to the environment. The growing energy consumption globally has
created a need for more energy-saving strategies. With climate change constituting a
significant hazard and a rising need for energy security, retrofitting buildings within the
construction sector would reduce by 18.4% the contribution of these buildings to global
GHG emissions (IPCC, 2014). Building retrofitting is also essential in reducing energy usage
worldwide, as phase-change materials may deliver a boosted energy efficiency with minimal
or no additional space required (Jelle and Kalnæs, 2017). Furthermore, building energy
retrofitting provides adequate opportunities for reducing building energy consumption,
improving cost and comfort, mitigating GHG emissions and aiding in the effective
utilization of energy by buildings (Shaikh et al.,2017).
In Europe, historical buildings comprise 26% of the total population, with 14%
constructed before 1919 and 12% between 1919 and 1945 (Tori, 2011). Over 40% of buildings
in the UK were built before 1960 (Bogdan and Tudor, 2011), with 22.7% being residential
buildings constructed before 1945 and 26.2% between 1945 and 1969 (EEA, 2020). These
historic buildings have not undergone any form of energy retrofitting over the years. The
average U-value of walls in residential buildings constructed between 1945 and 1969 is
1.39 W/m
2
K, while those built before 1945 have a U-value of 1.45W/m
2
K(Hao et al.,2020).
This has led toconsiderably higher energy consumption in these buildings compared to 21st-
century buildings. Estimates suggest that improving thermal comfort could save 180 Mt of
CO
2
annually (Hao et al.,2020). Britain has over 28 million homes contributing to about 15%
of the UK’s carbon emissions, and about 2=
3of the current building stock across has a huge
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possibility of standing by 2050; these buildings need to be retrofitted to meet the global net
zero targets which have been set by the UK government (Sadler, 2022). Various researchers
within the London School of Economics analysed that if all historically significant buildings
within the UK were retrofitted, the energy consumption of England would see a drastic
reduction of 1.3%, entailing a potential savings of about £1.7bn in energy consumption in
seven years and decrease in CO
2
emissions by 8.9 million metric tonnes (Saleem, 2020).
Building retrofits could involve numerous processes, including installing better insulation,
implementing energy-efficient glazing,upgrading lighting systems, optimizing water heating
and integrating heat pumps (Project Drawdown, 2020). Improving the energy efficiency of
buildings is both cost-effective and expeditious in reducing electricity demand, thereby
decreasing carbon emissions and enhancing public health and environmental air quality in
the local vicinity (Project Drawdown, 2020).
Moreover, incorporating techniques such as monitoring energy usage and water efficiency
in real-time, implementing green roofing, enhancing indoor air quality (IAQ), optimizing
operations and maintenance, enacting load curtailment initiatives, managing space utilization,
using virtual building automation systems and ensuring public transparency and
involvement are strategies that can be used during the renovation of a structure (Senseware,
2019). This approach transforms energy-efficient buildings into healthier, more productive
environments (Senseware, 2019). Sadler (2022) opines that retrofitting aids in creating
more thermally efficient buildings with high carbon efficiency and sustainability, making
these buildings cheaper in the long haul and having minimal need for maintenance.
2.1 The building “fabric first”approach
Understanding the performance of the building fabric (also known as the building envelope)
is critical for balancing energy consumption and plant size, maximizing comfort and
minimizing condensation, overheating and thermal stress concerns. To reduce heat loss and
enhance the energy efficiency of buildings, the building fabric is mostlyconsidered the most
important (Yang et al.,2022). The building fabric comprises all the components and
materials that make up the building. This includes the walls, floors, roofs, windows and
doors (Yang et al.,2022). The building fabric serves several functions, including protecting
occupants from weather conditions like wind, rain, sun and snow. The building fabric is also
essential for regulating the indoor environment regarding temperature, humidity and
moisture content (Korjenic et al., 2011). Building fabrics contribute significantly to a
building’s aesthetic and functionality (Klassen, 2006). Incorporating complexity and modern
materials such as architectural fabrics, active shading and high-performance glazing can
enhance structural performance while reducing energy consumption (Cole and Kernan,
1996). The building fabric usually containsopenings to provide physical access for daylight
admission and natural ventilation. This situation could hinder building performance in
certain instances due to potential security risks, privacy concerns or noise disturbances
associated with openings (Mohammad et al.,2022). Therefore, meticulous design
considerations are essential, particularly regarding the junctions between elements
comprising the building fabric, to prevent issues such as cold bridges between the internal
and external environments (Wastiels and Wouters, 2012). Furthermore, the thermal
performance of the building is influenced by the materials of the building fabric, which helps
to conserve energy, improve the environmental friendliness of buildings, extend periods of
indoor thermal comfort and reduce noise levels while fireproofing the building (Hung Anh
and P
asztory, 2021).
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2.2 Approaches for investigating building fabrics
Several researchers have proposed several methods for investigating building fabrics,
including thermal imaging (Kylili et al.,2014;Lin et al., 2022), in situ U-value (Tejedor et al.,
2019;O’Hegarty et al., 2021), air tightness testing (Carri
e and Wouters, 2012;Bahnfleth et al.,
1999), energy assessment (Cluett and Amann, 2015;Sun et al.,2021) and condensation risk
analysis (Nath et al.,2022;Koo et al.,2018), which is critical to guarantee that the building
improvement will not cause condensation and not impact IAQ.
2.2.1 Thermal imaging. Thermal imaging observes and measures temperature
fluctuations over surfaces (Lai et al., 2023). This method is valuable in assessing various facets
of building conditions and behaviours, offering a visual insight into structural weaknesses.
This, in turn, permits data acquisition and object analysis without necessitating sample
removal or causing harm to the object’s integrity (Doshvarpassand et al., 2019). Thermal
imaging cameras are primary tools for assessing various instruments, with multiple camera
options available for thermal imaging applications. These cameras evaluate electricity
distribution systems, electromechanical devices, buildings, roofs, tanks, pipes and valves
(He et al., 2021). Conducting a thermographic survey can readily identify flaws in underground
heating system pipes or tubes. When using a thermal imaging camera to identify inadequate
insulation or energy leaks, the temperature contrast between the building’s interior and the
outside should be at least 10°C (FLIR, 2011). However, a smaller temperature difference can
suffice if a thermal imaging camera with high image resolution and thermal sensitivity is
used. In colder climates, building inspections often occur in winter, while in warmer climates,
where verifying proper insulation to retain cool air from HVAC systems indoors is crucial, the
summer months offer an opportune timeframe for such thermal evaluations (FLIR, 2011).
Thermal imaging, or thermography, is crucial for visualizing heat energy through an
infrared camera (Glaze and Save, 2018). The images captured by the camera show
temperature variations across an area, from above absolute zero to net zero targets (Glaze
and Save, 2018). These images display various colours or shades of thermal patterns based
on the chosen colour palette (Glaze and Save, 2018). However, interpreting these patterns
requires proper knowledge of the environmental conditions during image capture and the
observed surface materials (Glaze and Save, 2018). The emissivity and reflectivity of an
object are two key properties that affect the reliability of thermal imaging (Shuvo, 2022).
Emissivity refers to an object’s ability to emit infrared radiation, while reflectivity is its
ability to reflect it. Materials with high emissivity tend to have low reflectivity, and vice
versa (Shuvo, 2022). Therefore, only materials with high emissivity can provide dependable
thermal readings because materials with low emissivity can reflect the temperature of
surrounding objects (Shuvo, 2022).
Older, non-retrofitted buildings often incur financial losses due to heat loss, particularly
in cold spots, which can lead to dampness and condensation, potentially causing damage to
building components (Roels and Tijskens, 2022). Thermal imaging is essential in identifying
these cold spots and areas of heat loss caused by air leakage (Roels and Tijskens, 2022). This
identification enables proactive measures to address the issue before it escalates (Roels and
Tijskens, 2022). More so, thermal imaging is non-invasive and, as such, requires no
dismantling or drilling of building elements. It is used without damaging the building fabric,
even without considering the difficulty of locating draughts and air leakages. At the same
time, moisture remains unseen unless it travels on walls, windows or roofs (Glaze and Save,
2018). Energy efficiency can also be improved by identifying unwanted heat transfer for
later correction in lesser periods while providing documentation that could include
inspection reports (Glaze and Save, 2018).
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2.2.2 In situ U-value testing. The In situ U-value testing explains how the thermal
transmission characteristics of building materials like walls, floors and roofs are measured
using a heat flow meter (Kim et al.,2022). The U-value measures how effectively building
elements or fabric prevent heat loss to the external environment, influencing building energy
efficiency (Zhang et al.,2020). Using the U-value in retrofit decision-making enables informed
choices regarding the necessary insulation levels before retrofitting and evaluating the
insulation’s performance after retrofitting (Zhang et al., 2020). The International Organization
for Standardization recommends ISO 9869 as the in situ U-value determination standard
(ISO) (Choi and Ko, 2019). The U-value can be established by several theoretical calculations,
either using simplified methods such as defined by the BS EN ISO6946 or through numerical
methods using detailed computer simulations which allow for a multifaceted heat flow
software such as TRISCO or a combination of both methods (Kosmina, 2016).
Theoretically, one could establish the U-value by using a heat flow meter to gauge the
heat movement across an element and noting the temperatures on either side under stable
conditions (Kosmina, 2016). However, practically assessing the thermal resistance (R-value)
or thermal transmittance (U-value) in contemporary residences presents challenges due to
several factors (Choi and Ko, 2019). Building materials often lack uniformity, and their
thermal conductivity remains uncertain. Accurately determining the dimensions of material
layers frequently involves damaging methods, which might not always be viable (Choi and
Ko, 2019).
The determination of the U-value involves several steps or elements. Firstly, it entails
choosing the right heat flow meters with a minimum accuracy of 65% (Zhang et al., 2020). It
is important to note that larger heat flow meters offer greater sensitivity but are more
challenging to mount on a wall. Secondly, selecting the appropriate temperature sensors is
crucial, with a minimum accuracy of 0.3 K (Zhang et al., 2020). These sensors should be chosen
based on the temperature to be measured; for instance, air temperature sensors are suitable if
the U-value is specified as the ratio of the density of heat flow rate to the air temperature
difference (Scarpa et al., 2017;Shinoda et al., 2021) rather than surface temperature sensors.
Thirdly, calibration of the heat flow meter and temperature gauges is necessary, ensuring it
has been conducted within the last 24months. Fourthly, the measurement phase involves
determining the measurement area, setting up temperature and heat movement sensors and
collecting data. Finally, data analysis is performed (Zhang et al., 2020).
2.2.3 Air tightness testing. Airtightness is the accepted technique for figuring out how
much air is wasted overall due to leaks in the envelope or fabric of a building (Schreiber
et al., 2021). Uncontrolled air leakage, accompanying ventilation energy losses, and occupant
thermal comfort are all impacted by how airtight a building’s envelope is (Recart and
Dossick, 2022). Gaining entry to an unoccupied dwelling is essential for an air-tightness
examination. Air testers use specialized blower door testing equipment, essentially large
fans affixed to an externalopening, like a doorway (Zheng, 2020). The structure is subjected
to pressurization through this setup while the testers assess pressure discrepancies.
Consequently, gaps and cracks permit external air pressure to infiltrate. Normally, the fan
decreases the internal pressure of the dwelling to a minimum of 60Pa (Sadler, 2021). Using an
anemometer, internal and external pressures are gauged alongside the fan’sefforttoestablish
the pressure variation. Sadler (2021) states that this method aids in pinpointing air leaks,
suggesting that the prevalence of such problems in sizable structures is likely to increase due
to the extensive range of potential leakage points. New, large, non-domestic buildings (about
1,000 m
2
floor space) are now obliged to fulfil a specific degree of airtightness under recent
amendments to UK building regulations (Stamp et al.,2020). The traditional method of
determining the airtightness of a building is through steady-state fan pressurization.
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According to some discussions in the airtight testing industry, the upper practical limit of large
buildings that can be tested may be around 5,000 m
2
; this is because of technical issues with
fan size, power requirements, transportation and noise (Feij
o-Muñoz et al.,2019).
2.2.4 Energy assessment. Energy assessment entails a thorough investigation into the
energy usage of homes and the variables that influence it (Wang et al.,2022). It involves an
inspection from the outside to the inside of a building, room by room (Bhamare et al.,2019).
Tools like the power logger, ultrasonic flowmeter, T4 temperature data logger, airflow
meter, thermal imaging cameras, IAQ meter, ultrasonic leak detector and flue gas oxygen
omega data logger are all used for energy assessment within buildings (Enerteam, 2017). A
room-by-room energy assessment is done throughout the house, along with a careful review
of previous utility invoices. Many comprehensive energy evaluations commonly incorporate
blower door examinations and a thermographic scan. Assessors might use tools such as
blower doors, infrared cameras, furnace efficiency meters and surface thermometers to
detect sources of energy wastage (Mauriello et al., 2019;Professional Home Energy
Assessments, 2022). This process generally involves several steps: an initial interview, an
outdoor survey, an indoor assessment, blower door and infrared assessments and a final
evaluation of outcomes (Neagu and Teodoru, 2019). The final assessment outlines
discoveries and specific measures for enhancing the energy efficiency of residences (Neagu
and Teodoru, 2019). These measures aim to align homes with net zero objectives, targeting a
20% reduction in energy consumption and greenhouse gas emissions (Neagu and Teodoru,
2019). In a new energy assessment era in the UK, new rules on energy efficiency will be
enacted in England and Wales. It would become mandatory that all commercially rented
properties possess an energy performance certificate (EPC) of at least E for buildings’
energy consumption to be within acceptable limits (Handels Banken, 2018).
2.2.5 Condensation risk analysis. Condensation is when airborne water vapour changes
from a gaseous state to a liquid state. Within structures, this occurs when warm and damp
air comes into contact with chilly surfaces that resist moisture (Sealy, 2022). Condensation
can seriously diminish the insulation’sefficiency and harm a building’s structural integrity.
An analysis of the risk of condensation on the roof or walls determines the possibility of
interstitial condensation. Building control frequently requests these calculations to verify a
person’s compliance with the regulations (BMI Group, 2021).
The change to solid walls can have issues that are not always obvious in achieving
carbon neutrality and increasing building energy efficiency (Martel et al.,2021). Suppose
nothing is in place to halt this vapour movement, either externally or internally with either a
vapour control layer or render. In that case, the existing walls will remain breathable and
capable of notwithstanding precipitation in their current state (Martel et al.,2021). When
internal insulation is upgraded, the entire wall dynamic is altered because heat from the
internal heat drive cannot dry the wall out, and vapour cannot travel through the wall
without passing through the insulation and vapour control layer (Martel et al.,2021).
Surface condensation develops on exposed surfaces and contributes to surface stains and
mould, which can typically be reduced with proper ventilation installation and use.
Interstitial condensation can develop between layers of a structure, such as within roof, wall
and floor components. This may result in the construction components degrading over time,
decreasing the building’s long-term safety, increasing the likelihood of mould growth and
lowering air quality (Ashby Energy Assessors, 2024). It can also potentially shorten the
building’s lifespan; hence, interstitial condensation must be avoided, or adequate ventilation
must be created to expel condensation (Libralato et al.,2019).
Numerous tools are accessible for conducting hygrothermal assessments, with the
requirement that a reputable British industry organization like Building Research
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Establishment (BRE) in the UK endorse the software. The recommended applications are
Flixo or Bisco for 2-D finite element analysis and Trisco for 3-D finite element analysis,
which are used for analyzing surface condensation risk. These tools analyse the dew
point line to ascertain the optimal placement of vapour control layers. They are crucial in
cold bridging computation (Saied et al., 2022). For the assessment of interstitial
condensation risk, tools like BuildDeskU (restricted to 1-D analysis using the Glaser
method) and HU-FI Pro (providing dynamic simulation for vapour diffusion but confined
to 1-D analysis focusing on straightforward scenarios rather than junctions) are used
(Saied et al., 2022). These instruments are useful, but they still have limitations, as all of
them, except the WUFI, identify vapour diffusion using the Glaser technique and assess
the risk using steady temperatures. This technique fails to incorporate the potential
impact of driving rain in its calculations, suggests unidirectional vapour movement (from
inside to outside) and overlooks porosity or absorption measurements, consequently
disregarding the potential risks related to moisture storage (Saied et al., 2022;Doda,
2020). Vapour diffusion determines how much water vapour can move through a
building’s structure and can also pinpoint the optimal placement for effective vapour
control and vapour-permeable membranes (Trifol et al., 2020). This ensures the well-
being of the building envelope, whether it involves roofs or walls. This, in turn, enhances
occupant health and diminishes factors such as heightened energy consumption in
buildings, among other benefits (Trifol et al., 2020;Proctor Group, 2023). Table 1
summarizes the advantages and disadvantages of the approaches.
3. Methodology
This paper examines many investigative methodologies necessary for setting realistic and
relevant objectives by assessing buildings’present fabric performance and energy
consumption. The research process followed a three-stage process presented in Figure 1.
3.1 Literature review
Firstly, when exploring methods to examine the UK’s existing building structures to
achieve net-zero targets, this study drew upon a narrative literature review. A narrative
literature review gathers existing research on a topic primarily through written text,
summarizing and elucidating findings from various studies. This textual method
essentially “tells the story”of the included studies, enabling an examination of
similarities, differences and relationships within the data and an assessment of evidence
strength (Popay et al.,2006). Although narrative synthesis lacks the structured
methodology of other review types, it remains a valuable starting point for research,
aiding in identifying trends and guiding future studies (Popay et al., 2006). This approach
proves particularly beneficial when statistical or formal methods of data pooling are not
feasible or suitable (Lisy and Porritt, 2016). A literature review is an objective and
thorough examination and critical evaluation of available research and non-research
literature related to the subject (Hart, 1998;Cronin et al., 2008). Its purpose is to provide
readers with a comprehensive understanding of current literature on a particular topic
and establish the groundwork for future endeavours, such as justifying further research.
Aproficient literature review gathers information about a specific subject from diverse
sources and is composed unbiasedly, devoid of personal biases. It should encompass a
well-defined search and selection methodology (Carnwell and Daly, 2001;Cronin et al.,
2008). A well-structured review enhances logical flow and readability (Colling, 2003). The
literature review was essential to explore the net zero targets, its benefits, retrofitting
buildings, the building fabric, the approaches for examining the building fabric and their
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advantages and disadvantages. The narrative review was conducted using various
academic databases, including but not limited to PubMed, Google Scholar and relevant
journals. The study encountered limitations in conducting the desk review, a common
aspect of such assessments. Challenges include the potential for bias and inaccuracies
stemming from the quality of available data. Addressing contextual factors like local
climate conditions and regulations may pose difficulties. Limited engagement with
stakeholders could result in overlooking practical insights and incomplete evaluation of
implementation challenges.
Table 1.
Analysis of the
investigative
approaches for
examining the
building fabric
Approaches Advantages Disadvantages
Thermal imaging 1. Due to its non-contact safety, usefulness
and effectiveness, it has many applications
(Kylili et al., 2014)
2. It can be used as a communication tool to
show home occupants where heat is lost
from buildings (Boomsma et al., 2016)
1. Images of certain items with variable
temperatures are challenging to
comprehend (Bednarkiewicz et al., 2021)
2. Unsuited for underwater objects and
glass (Lin et al., 2022)
In situ U-value
testing 1. High level of accuracy in testing building
envelopes (O’Hegarty et al., 2021)
2. Ability to reveal the feasibility
performance of buildings in various methods
or time series of analysis (Tejedor et al.,
2019)
1. Although it stands as a non-invasive
method, it can easily be categorized as
part of tests that make use of heat flow
meters (O’Hegarty et al., 2021)
2. Due to manual post-processing, it can
be relatively slow (Tejedor et al., 2019)
Air tightness
testing 1. Aids to improve overall operational and
environmental quality, especially of high-
raised buildings (Bahnfleth et al., 1999)
2. However, there is universal agreement
that air tightness testing warrants attention
in low-energy buildings as the energy
impact of envelope airtightness varies on
numerous aspects, including climate,
building consumption, ventilation system
type and air conditioning system usage
(Carri
e and Wouters, 2012)
1. They stand to have some level of
uncertainty in tall buildings concerning
wind pressure and stack effect
(Bahnfleth et al., 1999)
2. Parallel to this, worries about interior
air quality and structural damage have
sometimes led to additional regulations
beyond the conventional ventilation
criteria (Carri
e and Wouters, 2012)
Energy
assessment 1. It serves as an integral component of
water utility performance evaluation (Bylka
and Mroz, 2019)
2. Beyond energy savings, improved energy
efficiency has several advantages, such as
multi-family efficiency, health and comfort,
as well as improved work efficiency (Cluett
and Amann, 2015)
1. Assessment could be poorly done,
yielding poor and unreliable resources
(Carley and Konisky, 2020).
2. Consistent changes in technology,
tariffs and facilities affect
recommendations that make previous
audits outdated (Sun et al., 2021)
Condensation risk
analysis 1. Precise evaluation of potential surface and
interstitial condensation is crucial not only
for mitigating the detrimental impact of
moisture within building structures but also
for ensuring a mould-free and healthful
indoor environment (Mumovic et al., 2006)
2. To identify potential risks to building
systems (components) in various climatic
systems while potentially informing
building regulations (Nath et al., 2022)
1. It has many calculation methods, with
two (Glaser annual calculation and
monthly non-transient heat and moisture
calculation methods) prone to many
errors (Nath et al., 2022)
2. The accuracy of condensation risk
evaluation is dependent on the exactness
of calculated or measured temperatures
(Koo et al., 2018)
Source: Created by authors
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3.2 Case study selection
Using the case study method in this research allows for thoroughly examining complex
real-world issues, especially when understanding phenomena deeply within their natural
context. Case studies investigate specific phenomena using diverse data sources (Crowe
et al., 2011). This method enables a comprehensive exploration of multiple dimensions,
with implications for theory development and testing beyond the specific cases studied
(Baxter and Jack, 2008). The case study method offers several advantages, including its
ability to provide in-depth, detailed insights into complex phenomena or real-world
situations (Yin, 1984). Case studies also allow for examining rare or unique cases,
facilitating the exploration of topics that may be difficult to study using experimental or
survey-based approaches (Crowe et al., 2011). However, case studies also have
limitations. They often lack generalizability, as findings from a single case may not apply
to other contexts or populations (Tellis, 1997). Case studies can be time-consuming and
resource-intensive, requiring extensive data collection and analysis efforts (Yin, 1984).
ThecasestudiesinTable 1 were chosen to reflect a variety of investigative
methodologies used in investigating the existing building fabric. Each case study relates
to a particular method, such as thermal imaging, in situ U-value testing, air tightness
testing, energy evaluation and condensation risk analysis. The case study collection
looks broad, embracing several geographical regions within the UK and various types of
buildings, including residential, historic and institutional structures. This selection
process enables a comprehensive grasp of investigative approaches in various building
situations.
Furthermore, the study reliedon ten (10) case studies, 2 (two) for each approach essential
to understanding the current performance of the fabric and energy consumption of existing
UK buildings, as summarized in Table 2. The study considered various criteria to determine
which investigative approach best suits any case study. This included assessing whether
the chosen approach could provide the necessary detail and depth to address the research
questions effectively. Additionally, the study evaluated whether the investigative approach
could be easily integrated with other building systems or infrastructure in the UK, thus
minimizing building disruptions.
Figure 1.
Schematic
presentation of
research design
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existing
building fabric
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3.3 Case study analysis
The selection of case studies was based on previous research conducted by other scholars.
These case studies were chosen because they provided valuable information about the
various approaches for examining the building’s fabrics. By reviewing these case studies,
the researchers aimed to understand the current performance of building fabric and energy
consumption. The various assessment methods mentioned, such as thermal imaging, in situ
U-value testing, airtightness testing, energy assessment and condensation risk analysis,
were used to gather insightsfrom the selected case studies. The case studies were evaluated
using uniform steps such as background, problems, methods, findings and benefits. Thus,
through the case study data analysis, the research strategy raisesthe research from abstract
notions to real-world effects. The approach resonates with the context and challenges of net-
zero building retrofits, aligning methodologically with the precision of the study, unearthing
findings that tell a comprehensive story and ultimately offering practical solutions that can
drive the transformation of the UK’s building fabric.
3.4 Cross case analysis
Furthermore, the study used cross-case analysis to compare and contrast the two case studies
in each investigative approach. A cross-case analysis, as demonstrated in the studies of Shi
Chi Hai Hutong in Beijing by Gu and Ryan (2008), pertains to comparing and contrasting
different aspects of multiple case studies or situations. This analysis examines various
buildings, locations or historical periods to identify common themes or patterns that connect
them (Gu and Ryan, 2008). It allows for a comprehensive evaluation of the subject matter by
considering differences and similarities across different cases or scenarios, contributing to a
more holisticunderstanding of the topic. In the cross-case analysis, the study also considered
the implications of both case studies in each investigative approach. Cross-case analysis is
essential for understanding a subject from various angles. It helps find commonalities,
differences and general trends, making research more reliable and insightful.
4. Results and discussions
This section analyses the approaches for understanding the building fabric and energy
performance, including thermal imaging, in situ U-value testing, airtightness testing,
insulation, energy assessment and condensation risk analysis.
Table 2.
Various investigative
approaches and their
case studies
Investigative approaches Cases studies
Thermal imaging The Grove House, Roehampton, London (Sustainable St Albans, 2020;Grove
House, 2022)
St Julian Church, St Albans, Hertfordshire England (Historic England, 2009)
In situ U-value testing Lancaster West Estate, Central London (Jack, 2021)
Building Research Establishment (BRE) examining various England
residential binding (Hulme and Doran, 2014)
Air tightness testing Passivhaus properties (108 dwellings tested) (Zheng, 2020)
Ventilation assessment in cavity wall insulation in semi-detached bungalow
(Build Test Solutions, 2022)
Energy assessment York Energy Demonstration (Bell and Lowe, 2000)
Rose Cottage, Buttercrambe Estates (Historic England, 2022)
Condensation risk analysis Abbeyforegate Property, Shrewsbury (Browne, 2012)
Retrofitting Historic Buildings in Paisley Town (Proctor Group, 2023)
Source: Created by authors
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4.1 Thermal imaging
4.1.1 Case study –The Grove House. Background: The Grove House is on Roehampton
Lane, Roehampton, London, SW15 5PJ. A low-rise structure with an 800 m
2
ground floor
and 320 m
2
first floor that was initially constructed in 1777 by James Wyatt for Sir Joshua
Vanneck was upgraded with heating and insulation in the 1990s to satisfy UK standards. It
has two levels and 30 rooms. Building retrofits were carried out by Sustainable St Albans
(Sustainable St Albans, 2020;Grove House, 2022).
Problems: Significant problems with temperature regulation and deteriorated mineral
wood insulation were found across the structure. When the thermal imaging camera was
deployed in 2020, it revealed regions that needed more attention, and numerouschanges had
been made in those areas.
Method: A thermal map of the entire structure was created using a thermal imaging
camera to record the whole building and specific areas, like the ground and first-floor
pipework and corridors. The temperature data were then translated from the thermal colour
codes for use in building retrofits.
Findings: The most visible improvement was revealed in the underfloor heating, which
was fixed by providing adequate pipework for uniform heat distribution within the
building. The most noticeable difference is the underfloor heating, which is now functioning
properly with the pipes giving even heat distribution, as seen in Figure 2.
Moreover, the mineral wood insulation, which is 100mm thick, has degraded over the
years and was removed from some locations during retrofitting to facilitate fireproofing,
including metal lofts and access hatches. There was a distinct contrast between the ground-
floor and first-floor corridors. The substitute loft insulation was not yet installed, and the
photographs in Figures 3 and 4justify boosting the insulation in this building area (which
was not included in the restoration specification).
Benefits: Improved thermal performance of the building and reduced energy consumption
within the building.
4.1.2 Case study –St. Julian Church, St. Albans, Hertfordshire, England. Background:
St. Julian’s Church, located in St. Albans, Hertfordshire, England, is a flint structure with
stone accents believed to have been rebuilt in the 1950s to serve the cotton mill area. The
church consists of a nave, a north aisle, a chancel and a partially offset tower. Notable
features include 13th-century arches, a rib vault with moulded ribs supported by abaci
columns and a distinctive singing desk.The interior showcases box pews, a two-deck pulpit,
an organ in its gallery, a 14th-century chancel screen and the Lewknor family tombadorned
Figure 2.
The underfloor
heating is shown
before and after the
thermal imaging
photograph of the
retrofit
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with ogee mouldings and carvings. The unique layout includes a separate priest’s reading
station on the bottom deck of the pulpit (Historic England, 2009).
Problems: Increased energy consumption within the building was suspected to be a result
of leakages in the roof and outdated boilers due to its period of installation in 1950.
Method: The thermal imaging camera is again used to encompass the entire structure
and chosen spots for charting thermal bridges. A thermal bridge is a region where the
building’s envelope offers reduced thermal resistance (Quinten and Feldheim, 2019),
commonly due to construction limitations (Ge et al., 2021). Heat naturally seeks the path of
least resistance, following from heated spaces to the exterior. This approach was used to
identify regions with lower interior surface temperatures, potentially leading to issues like
condensation, particularly at corners. It helps detect notably increased areas of heat loss and
cold sections within buildings (Jiang et al.,2020). Figure 5 below shows a visible decline in
heat loss when blinds are Figure 6 illustrates that while the church has efficient double
glazing and a well-insulated roof, the metal window frames transmit cold air, and the main
doors need a new bottom seal.
Findings: There was a substantial decrease in heat loss when window blinds were closed.
Also, closed curtains and blinds could exhibit similar effects during double-glazing.
Findings also revealed that the roof was properly insulated. Also, thermal imaging of the
door shows that the seals need replacement as they allow seepage of cool air into the
building. Also, although the windows were double-glazed, which is very effective, window
Figure 3.
Is the first in the two-
story portion, where
the temperature is
spread equally
Figure 4.
The single-story
section (with the
original loft
insulation) shows the
underfloor heating
pipes, a wall-mounted
radiator and the
corridor’s actual
temperature
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frames conduct cold air, reducing the temperature and increasing energy consumption
within certain locations in the building (Sustainable St Albans, 2019).
Benefits: These improvements are reflected in the cost of heating and energy consumption,
which has drastically decreased by 15% from 16,200 kWh to about 13,500 kWh in three
months.
4.1.3 Thermal imaging cross-case analysis. Cross-analysis of the two thermal imaging
case studies, “The Grove House”and “St Julian Church”, reveals several commonalities and
differences in their approaches, findings and benefits:
4.1.3.1 Commonalities. Both case studies use thermal imaging cameras as part of their
methodology to evaluate the buildings’thermal performance, identifying areas of heat loss
and temperature variations. Their shared objective is to enhance the energy efficiency of the
structures by addressing these thermal issues, guided by the thermal imaging results, which
inform retrofitting decisions aimed at improving insulation and reducing energy
consumption. Furthermore, thermal imaging identifies specific thermal deficiencies within
both buildings, including problems related to insulation, heating systems and thermal
bridges, all of which contribute to potential energy inefficiency. To effectively communicate
their findings, both studies use visual documentation, including photographs, to illustrate
the identified issues and the subsequent improvements made to the structures.
4.1.3.2 Differences. Grove House (built in 1777) and St. Julian Church (rebuilt in the 1950s)
differ in building type and age, influencing their thermal issues and retrofit processes. Grove
Figure 5.
Photo taken from
inside the church
with the blinds closed
(left) and Photo taken
from inside the
church with the
blinds open (note,
heating pipe on the
right –yellow) (right)
Figure 6.
The view taken from
inside the windows
shows that, while
double glazing is
quite efficient, the
metal window frames
convey chilly air (left)
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House deals with underfloor heating and insulation issues, while St. Julian Church addresses
heat loss through windows and thermal bridgestailored to their unique construction and use.
The St. Julian Church study delves into thermal bridges related to window frames and blinds,
while Grove House does not mention thermal bridge assessment. Grove House notes
improved thermal performance without specific energy savings data regarding retrofit
outcomes.At the same time, St. Julian Church achieves a significant 15% reduction in energy
consumption over three months, dropping from 16,200 kWh to about 13,500 kWh.
4.1.3.3 Implications. These case studies showcase thermal imaging’s adaptability in
detecting thermal issues across various building types. They underscored the significance of
addressing specific thermal problems for improved energy efficiency and reduced heating
costs. Although both studies generally report positive retrofit outcomes, the extent of energy
savings can differ significantly, emphasizing the importance of tailored solutions. The
distinctions between these cases highlight the necessity of customized approaches to
thermal retrofit projects based on each building’s unique characteristics.
4.2 In situ U-value testing
4.2.1 Case study –Lancaster West Estate, Central London. Background: Building performance
measurement was given by Build Test Solutions, a UK-based company, to help with building
design, ensure construction quality and deliver important lessons and feedback to the
Lancaster West Estate (Jack, 2021). Built in the middle of the 20th century, the Lancaster
West Estate is a collection of medium-rise apartment buildings located in North Kensington
in West London. It is in the Notting Dale suburb, which endured V-2 shelling during the
Second World War. Due to the slum cleaning programme of the 1960s, it was built as
municipal housing. Theestate was created by architects Clifford Wearden and Peter Deakins
in 1963–1964 as a significant Royal Borough of Kensington and Chelsea redevelopment
project, but it was later significantly altered and scaled back in ambition East of Latimer
Road tube station. (Glendinning and Muthesius, 1994;GmbH, Emporis, 2017).
Problems: The standards of insulation and artistry led to a negative impact on the
U-value. Also, poorly fitted insulation, air leaks, cold badging fromwall tiles and the diverse
thermal properties of mortar joints all affect the U-value of the property. Government energy
targets and affordable housing goals compelled authorities to re-evaluate the energy
efficiency of their structures and search for alternative ways to add space to pre-existing
structures. Due to this, the district heating system’s frequent breakdowns serving the finger
blocks were visible (Jack, 2021).
Methods: The total thermal performance of the buildings was measured using
SmartHTC to calibrate energy models that would be used in the retrofit design and identify
homes where the performance is significantly different from what is expected.
Measurements of pre-retrofit, thermal performance, air permeability, U-value, temperature
and external thermography of buildings were measured. Also, post-retrofit, the same
parameters were measured. After measurements were collected, retrofits would be made
based on the findings (Jack, 2021). Figure 7 uses thermography to identify high heat loss
areas and evaluates insulation levels with Heat3D and the U-Value Measurement System.
Results: improved thermal performance for dwellings and walls was better than pre-
retrofitted walls, allowing for less costly specifications to achieve the net zero aims of the
project. Also, U-value measurement results were added to the council asset management
system (Jack, 2021).
Benefits: To make homes carbon-neutral by 2030, the energy required for heating and
powering appliances was supplied by retrofitting the buildings with solar panels and
air-sourced heat pumps. This, in turn, reduces energy consumption bills and levels.
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4.2.2 Building research establishment examining various England residential bindings.
Background: As of 2021, in England, there were about 25 million homes (Statista, 2024).
About two-thirds of these are cavity walls, while one-third are solid walls, such as those of
solid brick, stone and concrete (Raushan et al., 2022). To effectively measure the energy
consumption of the housing stock and to evaluate the potential for energy savings, it is
critical to understand how walls of various sorts function in real-world settings. The
Department of Energy and Climate hired the BRE to examine the thermal performance of
walls in a variety of English residential buildings and to compare measured U-values to
theoretically derived values (Hulme and Doran, 2014).
Problem: A lack of realistic estimates of building energy consumption has led to
increased energy consumption and an inability to quantify the potential for energy
efficiency improvements within these buildings.
Method: Heat fluxes (heat losses) through structural components like walls. U-values in
about 300 solid walls, unfilled cavity walls and filled cavity wall houses were measured
through the in situ monitoring of heat flow and temperatures. The field observations were
also used to calculate theoretical U-values. The values that were calculated and measured
were then contrasted. Homes previously visited as part of the 2010–2011 English Housing
Survey (EHS) were chosen for these measurements (Hulme and Doran, 2014). Figure 8
shows the setup in an occupied home, with heat flux plates and temperature sensors
supported by clamps andteleports and a tiny tag datalogger mounted on an exterior wall.
Results: The primary U-value examination in 2011–2012 unveiled a surprising finding
regarding certain walls. These walls were initially categorized in the EHS as belonging to homes
with predominantly uninsulated cavity walls, yet their U-values were unexpectedly low. This
raised the possibility that these walls might have been insulated after all. There is a notable
disparity between the average measured U-values (both mean and median) and the computed
U-values for insulated hollow walls and the two types of solid walls. For insulated cavity walls,
the measured U-values surpass the calculated values, implying that these walls seem to be
performing less efficiently than the theoretical estimation suggests. Conversely, the measured
U-values for solid walls are lower than the calculated values. Nevertheless, measurements
indicate that uninsulated hollow walls correspond closely to the calculated values (Hulme and
Doran, 2014). Figure 9 captures the heat distribution and performance of the equipment installed
on a building wall, highlighting areas of thermal activity and potential heat loss or efficiency.
In this case, the wall’s thermal performance is exceptionally inconsistent; thus, choosing
a representative measurement point at a temperature close to the average for the wall as a
whole was required.
Benefits: One of the most significant factors influencing a home’senergyefficiency assessment
is the amount of heat lost through the building’s envelope. Estimating and correctly diagnosing
Figure 7.
Use of External
thermography to
highlight areas of
particularly high heat
loss (left) and Heat3D
and the U-value
Measurement System
were used to measure
U-values to
understand the
current condition of
the walls, floors and
ceilings and to
provide information
for the specification
of extra insulation
(right)
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the amount of heat generated by structures is also crucial. The U-values of buildings are a factor
that can overestimate a building’senergyefficiency because they represent a building’soriginal
design values and thermal characteristics, which determine the thermal performance of an
existing building. Therefore, the use of the above method aids in achieving net zero targets by
accurately measuring a building’s energy consumption, hence assisting in the general reduction of
energy consumed if the recommended retrofits are put in place (Park et al., 2021).
4.2.3 In situ U-value testing cross-case analysis. Cross-analysis of the two case studies
on in situ u-value testing, “Lancaster West Estate”and “Building Research Establishment
(BRE) Examining Various England Residential Buildings”reveals commonalities and
differences in their objectives, methods, findings and benefits:
4.2.3.1 Commonalities. Regarding the in situ u-value testing, the two case studies,
“Lancaster West Estate”and “BRE Examining Various England Residential Buildings”,
share common objectives and methods. Both studies aim toassess thermal performance and
measure U-values to enhance energy efficiency. They use in situ testing and various
equipment for data collection, focusing on comparing measured U-values to theoretical
values to inform energy-efficient retrofits. This emphasizes the significance of accurate U-
value measurements for achieving energy-saving objectives.
Figure 9.
A thermal image of
the apparatus
mounted on a wall in
a building
Figure 8.
The apparatus set up
in an occupied home
(left-hand image),
with clamps and
teleports (blue poles)
supporting the heat
flux plates (red discs)
and indoor
temperature sensors
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4.2.3.2 Differences. The two case studies, “Lancaster West Estate”and “BRE Examining
Various England Residential Buildings”,differinscope,buildingtypes,specific issues
addressed and reported retrofitoutcomes.“Lancaster West Estate”is limited to a particular
housing estate in London, focusing on medium-rise apartment buildings and addressing
issues like poorly fitted insulation and air leaks. It reports improved thermal performance and
reduced energy consumption. In contrast, the “BRE Examining Various England Residential
Buildings”study encompasses a broader range of residential buildings across England,
including various building types and specific issues related to unexpected variations in
U-values. However, it does not provide particular retrofit outcomes but emphasizes the
importance of accurate U-value measurements for energy efficiency assessment.
4.2.3.3 Implications. Both case studies emphasize the importance of accurate U-value
measurements for assessing thermal performance and enabling energy-efficient retrofits. The
“Lancaster West Estate”study showcases the practical applicationof U-value measurements
in achieving energy-saving and carbon-neutral objectives. On the other hand, the “BRE
Examining Various England Residential Buildings”study highlights the awareness of
potential U-value variations and the necessity for meticulous monitoring and component
analysis. While the challenges and solutions discussed are pertinent to various residential
building types, the specificretrofit outcomes and goals may differ based on the project’s
scope and objectives.
4.3 Air-tightness testing
4.3.1 Case study –Passivhaus Properties (108 dwellings tested). Background: 108 dwellings
in England were tested for potential air leaks by Build Test Solution. This work was
completed in a reasonably short time as a reaction to the future home standard consultation,
which suggests a lower limit of 1.5 m
3
/h/m
2
@50Pa on the pulse method.
Problem: An issue that came up during previous lab-based tests of extremely airtight
enclosures where agreement between the fan technique and pulse was being looked at. In
each of these situations, we observe that the pressure pulse takes longer to reach its peak
and that the decay rate also slows down significantly. Early implementations of the pulse
technology experienced calculation difficulties for extremely airtight houses due to this
shape change; timings became out of phase and the measurement procedure’s important
“quasi-steady”portion was not reliably recorded (Zheng, 2020).
Method: All intended openings were sealed, doors and windows were closed and traps
were filled following BS EN ISO 9972:2015’s Building Preparation Method. The connection
between the blower door frame and the door frame was also taped up using airtight tapes
during the blower door testing to reduce any leakage around the blower door unit. Once
everything was in place, a certified test engineer ran a blower door fan test in pressurization
and depressurization modes. Following the removal of the door fan, pulse tests were
conducted soon after in each property, using the most recent hardware and software
configurations (Zheng, 2020).
Findings: The data set shows an average difference between the blower door fan
technique and pulse of 0.0003m
3
/h/m
2
@4Pa. This amounts to an absolute percentage of
11%, broadly in line with expectation given the ISO 9972:2015 declared measurement
uncertainty of the fan technique at 10%, the pulse measurement uncertainty at 5% and the
additional uncertainty associated with Power Law extrapolation. This suggested areas for
improvement in building envelopes due to uneven window and door seal sitting (Zheng,
2020). Figures 10,11 and 12 reveal the air tightness testing in various locations by Build
Test Solutions in England.
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Figure 10.
Blower fan set up in a
doorway and taped
from inside
Figure 11.
(L-R) Complete 40 L
pulse set-up used in
this configuration for
all text cases; blower
door fan mounted and
sealed in a panel cut
to the size of the
window opening
Figure 12.
Pulse and blower
door fan testing in a
small 94 m
3
art studio
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Benefits: Building envelopes must be properly sealed to enhance energy performance
and distribution in diverse buildings, according to testing of a building’s airtightness. It
is common knowledge that airtightness improves occupant comfort, IAQ, durability and
liability for building proprietors. However, lowering energy use in the built world is a
measurable objective (sadia_badhon, 2020). Also, setting a lower operational limit of
1.5m
3
/h/m
2
@50Pa is not essential because Pulse can monitor extremely airtight houses
just as well as the current blower door fan technology. Regardless of the measurement
technique, measuring particularly airtight buildings might not be easy (Zheng, 2020).
4.3.2 Case study –ventilation assessment in cavity wall insulation in semi-detached
bungalow. Background: A semi-detached bungalow’s cavity wall insulation was installed by
Dyson Energy Services using a preliminaries, assessment, design (PAS) 2035 compliant
procedure. Therefore, having completed training offered by the Insulation Assurance
Authority, Dyson did airtightness measurements before and after the retrofit, using Pulse to
make an informed judgement on what further ventilation requirements were needed (Build
Test Solutions, 2022).
Problem: Because cavity wall insulation can lessen a building’s air permeability, it is
crucial to examine if enough ventilation will supply enough fresh air when the insulation is
placed (Build Test Solutions, 2022).
Method: The air permeability of each room was measured using a pulse because, even
though a building may have enough ventilation throughout, some rooms may not, putting
them at risk of condensation or mould growth (Build Test Solutions, 2022). Figures 13 and 14
show air tightness testing with apparatus mounted with indoor readings.
Findings: Theoverallairpermeabilityofthehousebeforetheretrofit was 1.69 ACH@4Pa
(1/h). Following the refit, this figure significantly decreased to 1.15 ACH@4Pa (1/h),
underscoring the importance of considering ventilation even with individual modifications.
The measured air permeability of each room exceeded 1.5 ACH@4Pa (1/h), suggesting
sufficient ventilation for the entire building and each specificroom(
Build Test Solutions, 2022).
Benefits: Measurements allowed for the insulation installer to adhere to PAS2035:2019 and
to do the cavity wall insulation installation in a way that considers the dangers associated
with a loss of ventilation. The measurements showed that the building and its rooms
continued receiving enough fresh air through infiltration even after installing a single measure
Figure 13.
(L-R) retrofitted
building: a very low
min fan is required
for the fan tests, with
a large restrictor plate
fitted
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of cavity wall insulation. As a result, it was unnecessary to take extra ventilation measures
like installing trickling vents and undercutting interior doors (Build Test Solutions, 2022).
4.3.3 Air tightness cross-case analysis. The study performed a cross-analysis of the two
case studies on air-tightness testing, “Passivhaus Properties”and “Ventilation Assessment
in Cavity Wall Insulation in Semi-Detached Bungalow”, to identify commonalities and
differences in their objectives, methods, findings and benefits:
4.3.3.1 Commonalities. Both case studies share common objectives, methods and
benefits of air-tightness assessment. Their primary aim is to evaluate the airtightness of
buildings, identifying potential air leaks and ventilation needs. They use the pulse
method for air-tightness measurement in both cases, conducting pre- and post-retrofit
testing to assess the impact of insulation measures on airtightness. The studies
underline the significance of measuring airtightness for enhancing energy performance,
ensuring occupant comfort, maintaining IAQ and meeting building standards and
regulations.
4.3.3.2 Differences. The “Passivhaus Properties”and “Ventilation Assessment in Cavity
Wall Insulation”case studies differ in scope and specific issues addressed. The former
involves testing 108 dwellings in England to assess airtightness and compares pulse
measurements to the fan technique, emphasizing technical challenges and measurement
comparisons. In contrast, the latter focuses on a specific semi-detached bungalow to assess
the impact of cavity wall insulation on air permeability, primarily highlighting the need for
ventilation during insulation installation. The “Passivhaus Properties”study provides data
on measurement differences. In contrast, the “Ventilation Assessment in Cavity Wall
Insulation”case study focuses on pre- and post-retrofit air permeability values to showcase
the effect of insulation on airtightness.
4.3.3.3 Implications. Both case studies underscore the practical application of the
pulse method for air-tightness measurements, offering a valuable tool for assessing and
enhancing building performance. The “Passivhaus Properties”study addresses
challenges in using Pulse for extremely airtight houses and confirms its effectiveness for
monitoring such buildings. Conversely, the “Ventilation Assessment in Cavity Wall
Insulation”case study highlights the need to prioritize ventilation during retrofits to
safeguard IAQ and prevent condensation problems. Both studies emphasize the
significance of measuring airtightness for achieving energy efficiency and meeting
building standards and regulations.
Figure 14.
MVHP units
switched off with
both inlet and
exhaust sealed
internally or
externally
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4.4 Energy assessment
4.4.1 Case study –York Energy Demonstration Project. Background: The York Energy
Demonstration Project was used in Bell and Lowe’s (2000) study on energy-efficient housing
modernization while discussing the implications for modernizing low-rise buildings in the
UK. The assessed property was three- and two-bedroom, semi-detached, terraced houses
built in the 1930s or 1950s. The structure consists of load-bearing cavity brickwork
accompanied by a pitched tile roof. Ground floor constructions encompass a combination of
solid and suspended timber elements. The floor area spans from 75 to 95 square meters. The
loft insulation installed in the early 1970s varied in thickness, ranging from 25 to 100 mm,
and no additional insulation was incorporated subsequently (Bell and Lowe, 2000).
Problems: The primary heating source for most houses was a gas fire in the main living
area. At the same time, hot water was generated through an immersion heater connected to
an insulated cylinder. A few homes, established in the 1970s, featured electric storage
heaters and an electric fire in the main living room. These residences used an insulated
storage cylinder to store hot water heated by an immersion heater designed to function
during off-peak electricity periods (Bell and Lowe, 2000).
Method: Data from the building was collected for review, enabling the operator to
perform various measurements that would allow him to define a “zero point”corresponding
to the existing elements that still need to be improved. With the help of a thermal camera,
the expert can measure the energy losses of the house. Adequate retrofits and renovation
plans are made and then implemented and monitored before reports are made about the
building’s energy consumption and improvements (Bell and Lowe, 2000). Table 3 compares
gas consumption across all schemes, Table 4 details the heat loss coefficient (W/K) by
element, and Figure 15 illustrates the energy characteristics of 30 house study groups.
Results: Retrofits of solar panels and air vents were done to the building to reduce energy
consumption. It was discovered that the house that initially consumed 34,109kWh of energy
Table 3.
Comparison of gas
consumption –all
schemes
Before improvement Improvement to tenants choice standard
Group
Gas Elec. Total Gas Elec. Total
kWh kWh kWh kWh kWh kWh
Experimental 26,946 7,944 34,890 27,864 3,246 31,110
Control 26,290 7,818 34,109 27,851 3,081 30,932
Difference 656 126 781 13 165 178
Source: Bell and Lowe (2000)
Table 4.
Heat loss coefficient
(W/K) broken down
by element
Element
Before After
Mean % Mean %
Floor 25 11 25 17
Wall 83 37 37 25
Windows and doors 47 21 40 28
Roof 20 9 9 6
Fabric heat loss coefficient 125 78 111 77
Ventilation heat loss coefficient 50 22 34 23
Total heat loss coefficient 225 100 145 100
Source: Bell and Lowe (2000)
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99
before retrofit now consumed only 30,932 kWh after retrofit and had a consistent decline in
energy consumption.
Benefits: The energy consumption of buildings can be reduced with proper retrofitting
strategies for long-term care of buildings. From the base load of energy consumed, more power
is consumed during winter and festive periods due to increased activities. More so, noon has
minimal daily energy consumption. Hence, retrofits would aid in balancing energy
consumption, while residents should be educated on energy-conservative techniques (Bell and
Lowe, 2000).
4.4.2 Case study –Rose Cottage, Buttercrambe Estates. Background: Energy performance
certification was used to examine the energy efficiency of some buildings in England. The
minimum energy efficiency standards working group, which included the National Trust
(chair), Country Land and Business Association, Central Association for Agricultural Valuers,
The Landmark Trust and other stakeholders, conducted this to provide evidence of the
problems with EPC assessments for traditionally constructed buildings and identify the
obstacles to effective energy efficiency improvements (Historic England, 2022). Figure 16 shows
the Rose Cottage in 2021 (a three-bedroom semi-detached cottage from the 18th century built of
coursed Hardwick stone with a brick lean-to and chimney stacks with a floor space of 78 m
2
.
Problem: Before the refurbishment, neither of the properties had been updated. The
cottage had single glass throughout, no floor or wall insulation, open-hearth fires and rear
boilers for heating. Their toilets and kitchens were old (Historic England, 2022).
Method: EPC baselines were completed to be compared to post-renovation evaluations.
Rose Cottage G16 ratings (Historic England, 2022).
Results: Rose Cottage had a complete renovation with the same work criteria. This
comprised loft insulation, replacement double-glazed windows, insulated doors, full interior
dry lining with a Kingspan product, floor insulation and underfloor heating. Each home has
a Mitsubishi Ecodan ASHP installed (Tables 5 and 6).
Benefits: Since then, greater benefits from solar gain through French doors have created a
warmer environment. Newly advised measures include solar heating, 2.5 kWp solar
photovoltaic panels and heat recovery systems for mixed showers (Historic England, 2022).
Figure 15.
Energy
characteristics of 30
House study groups
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4.4.3 Energy assessment cross-case analysis. The study performed a cross-analysis of
the two case studies on energy assessment, “York Energy Demonstration Project”and “Rose
Cottage, Buttercrambe Estates”, to identify commonalities and differences in their
objectives, methods, findings and benefits:
4.4.3.1 Commonalities. Both case studies share common objective of assessing and
enhancing the energy efficiency of residential buildings in England. They use energy
assessment methods to evaluate and compare the energy consumption of the buildings
before and after retrofit activities, effectively measuring the impact of energy-saving
measures. Both studies’pre- and post-retrofit evaluations reveal that retrofits result in
reduced energy consumption, improved energy performance and increasedresident comfort,
underscoring the benefits of such measures.
4.4.3.2 Differences. The “York Energy Demonstration Project”and “Rose Cottage,
Buttercrambe Estates”case studies differin scope and energy sources. The former evaluates
Figure 16.
Rose Cottage in 2021
(a three-bedroom
semi-detached
cottage from the 18th
century built of
coursed Hardwick
stone with a brick
lean-to and chimney
stacks)
Table 5.
Reveals EPC
assessment summary
for Rose Cottage
EPC date October 2012 June 2015 January 2016 April 2019
Rating F36 E39 F22 E44
Flor Area 90 m
2
137 m
2
104 m
2
124 m
2
Walls Sandstone, solid
brick, timber frame Sandstone/limestone,
solid brick Granite/whinstone Sandstone/limestone,
timber frame
Roof Partial roof insulation No roof insulation No roof insulation Partial roof insulation
Windows Single glazed Single glazed Full secondary
glazing Full secondary
glazing
Main heating Oil ASHP ASHP ASHP
Main heating
controls Programmer, TVRs
and bypass Programmer, TVRs
and bypass Programmer and
room thermostat Programmer and at
least two room
thermostats
Lighting 86% low energy
lighting 89% low energy
lighting 38% low energy
lighting 83% low energy
lighting
Source: Historic England (2022)
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the energy-efficient modernization of houses from the 1930s and 1950s, focusing on heating
systems, insulation and energy conservation. In contrast, the latter centres on renovating an
18th-century cottage, emphasizing air-source heat pumps and energy-saving technologies.
The studies also differ in energy consumption data, with the York project providing detailed
gas and electricity consumption figures before and after retrofit. At the same time, Rose
Cottage uses EPC ratings to demonstrate energy improvements.
4.4.3.3 Implications. Both case studies emphasize the benefits of energy-efficient retrofits
in residential buildings, showcasing their positive impact on energy consumption and
performance. The “York Energy Demonstration Project”stresses the importance of addressing
heating systems, insulation and energy conservation to reduce energy consumption. In
contrast, the “Rose Cottage”study highlights the potential for substantial energy performance
improvements by installing modern technologies like air source heat pumps and solar panels.
Both studies underscore the significance of conducting energy assessments and comparing
pre- and post-retrofit evaluations to gauge the effectiveness of energy-saving measures.
4.5 Condensation risk analysis
4.5.1 Case study –Abbeyforegate Property, Shrewsbury. Background: As part of the society
for the protection of ancient Building Performance Survey, the property on Abbeyforegate
underwent monitoring before and after renovations. The brick structure dates to circa 1820; it
was originally mid-terrace, but one of the next buildings was removed. The structure has two
floors and an attic dormer, with a usable floor space of roughly 60 m2. Shrewsbury’s“brick
and a half thick”walls are 400mm thick and constructed using a Flemish bond. The pointing
is worn in many areas, and the lime-based mortar joints are around 10 mm wide (Browne,
2012).
Problem: Driven rain will collect in the open mortar joints if the wall is left as it is, so it
needs to be repointed in a suitable material to shed water better. Traditional structures’
internal “common”bricks are frequently of lower quality, with less consistent shape and less
frost resistance (Figure 17).
Method: This study examines interstitial moisture and the design U-value of the south-
facing ground floor wall at the Abbeyforegate property in Shrewsbury using WUFI Pro 5.1
software. Thermal transmittance is modelled for pre- andpost-renovation scenarios to determine
whether critical moisture limitations are achieved at the internal wall insulation (IWI) and
Table 6.
Reveals EPC
assessment summary
for Rose Cottage
contd
Feature Description Rating
Wall Sandstone or Limestone, as built, no insulation (assumed) Very poor
Wall Timber frame, as built, partial insulation (assumed) Average
Roof Pitched, 150 mm loft insulation Good
Roof Pitched, no insulation (assumed) Very poor
Roof Flat, no insulation (assumed) Very poor
Window Full secondary glazing Good
Main heating Air source heat pump, radiators, electric Good
Main heating control Programmer and at least two room thermostats Good
Hot water From main systems Very poor
Lighting Low energy lighting in 83% of fixed outlets Very good
Floor Solid, no insulation (assumed) N/A
Secondary heating Room heaters, dual fuel (mineral and wood) N/A
Source: Historic England (2022)
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masonry wall contact. Investigations into microbial growth on the inside surface of the
wall were not conducted (Browne, 2012).
Findings: These spaces would offer a capillary moisture break and lower the U-value of
the wall. The wall is simulated as a solid wall with a complete link between all components
because the voids will not be constant enough to form a continuous cavity. Worst-case
situations for high U-values and moisture levels are likely to be shown in Figure 18, which is
the pre-refurbishment assignment of material. After the renovation, the wall interior has an
additional 40 mm of wood fibre insulation. This is divided into two layers, one 5mm thick
and the other 35 mm thick, allowing for monitoring the overall water content of the
vulnerable inner 5mm layer. As the wall gets thicker, the peak water content of the
insulation contact falls. The mortar’sinfluence is demonstrated to have no impact on
the 215 mm wall and only slightly raises the peak water contents of the 377 mm wall IWI.
Benefits: Reduced condensation risks within the structure were achieved, accompanied
by suggestions to account for uncertainties in both internal and external climates. These
Figure 17.
Bricks at Shrewsbury
laid in a “brick and a
half thick”Flemish
bond (left) plan view
showing half batts’in
the centre of the wall
(right)
Figure 18.
Pre-refurbishment
assignment of
materials (23%
mortar in a brick-and-
a-half thick wall
represented in a one-
dimensional
simulation)
United
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103
include decreased indoor temperatures, alterations in ventilation levels, susceptibility to
wind-driven rain and heightened rates of internal moisture generation. The condensation
risk analysis also enhanced the property’s air exchange rate (Browne, 2012). Figure 19
illustrates the distribution of materials following refurbishment, specifically demonstrating
how the simulation models wood fibre insulation.
4.5.2 Case study –retrofitting historic building in Paisley Town. Background: The
Townscape Heritage Conservation Area Regeneration Scheme of Renfrewshire Council is
assisting with restoring a significant historic structure in the heart of Paisley that had
become run-down. The building, a grade B-listed stone-faced terraced structure with a slated
roof that dates to 1840, is locatedat 3 County Place and directly across from Paisley Gilmour
Street train station (Proctor Group, 2023).
Problem: Condensation accumulated due to moisture infiltration via the roof and building
walls. Two levels of the structure have been emptying for over 20years, and upcoming roof,
stone and window external repairs are needed to address the potential condensation
concerns.
Method: To protect the roof from damage, a new roofing membrane, new leadwork and
the reuse of the existing slates were all incorporated into the roof work. To maintain the
aesthetic of the neighbouring buildings, all of the front elevation’s existing slates were kept,
and CUPA H3 slate was added to the back. The roof’s sarking will be completely replaced
(Proctor Group, 2023).
Results: In Figure 20, the new roofing structure allows for high levels of airflow in
addition to the transportation of moisture vapour, making the formation of condensation in
the roof space practically impossible, despite the complexity of the roof structures of historic
buildings and the sensitive nature of the careful consideration of moisture management and
Figure 19.
Post-refurbishment
assignment of
materials
(representation of
how wood fibre
insulation is modelled
in the simulation)
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condensation control. It has a very high level of air and vapour permeability; therefore, it can
function in environments where airtight alternatives cannot (Proctor Group, 2023).
Benefits: Improved ventilation and thermal performance of the building while preserving
and protecting historic building fabric Proctor Group, 2023).
4.5.3 Condensation analysis cross-case analysis. The study performed a cross-analysis of
the two case studies on condensation risk analysis, “Abbeyforegate Property, Shrewsbury”
and “Retrofitting Historic Building in Paisley Town”, to identify commonalities and
differences in their objectives, methods, findings and benefits:
4.5.3.1 Commonalities. Both case studies aim to address condensation issues in historic
or traditional buildingsto enhance thermal performance and minimize condensation-related
risks. They both deal with historic or traditional structures, acknowledging the delicate
balance required for modernization while preserving heritage. Using energy modelling
through simulations and software like WUFI Pro 5.1 and roofing membrane analysis, they
assess U-values and moisture risk. The primary emphasis in both cases is on mitigating
condensation risks, especially in areas susceptible to moisture infiltration.
4.5.3.2 Differences. The “Abbeyforegate Property”and “Retrofitting Historic Building in
Paisley Town”case studies differ in terms of location and building type, with one focusing
on a brick structure in Shrewsbury and the other on a stone-faced terraced building in
Paisley. The strategies to mitigate condensation also diverge, with the former emphasizing
wall insulation and masonry properties and the latter addressing the roofing system with a
focus on ventilation and moisture management. The “Abbeyforegate Property”concentrates
on wall condensation risk, while the “Paisley Town”study deals with condensation in the
roof space. Different materials and techniques are used, including wood fibre insulation and
moisture behaviour analysis for the former, roofing membrane, CUPA H3 slate and new
leadwork for the latter.
4.5.3.3 Implications. Both case studies underscore the significance of managing
condensation risk in historic or traditional buildings prone to moisture-related issues.
Material selection, insulation and moisture management techniques are adaptable based on
Figure 20.
Use of roofing
membrane to address
condensation risk
analysis in a historic
building located in
Paisley
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existing
building fabric
105
location and specific building components. Effective simulations and analytical tools are
vital for assessing and mitigating condensation risk in heritage structures. Furthermore,
improving the thermal performance of building elements, whether walls or roofs, is pivotal
in reducing condensation risk and preserving historic fabric.
5. Conclusions and recommendations
In conclusion, the study examined approaches to investigating the UK`s existing building
fabric to pursue net zero targets. A fact from the survey is that most of the buildings that
will be used in 2050 and 2070 to achieve the net zero target already exist. A fact from the
study is that most of the buildings that will be used in 2050 and 2070 to achieve the net zero
target already exist. UK emissions are 77% attributable to residential heating, 14% to
commercial buildings, and 10% to public sector assets. This will negatively impact the Net
Zero targets if the trend is not addressed. The significance of the study underscores the
importance of comprehending the advantages, drawbacks and cooperative potentials of
investigative methodologies in developing economical energy performance strategies. It
highlights the pressing necessity to eradicate carbon dioxide (CO
2
) and GHG emissions to
address global warming effectively and adhere to the 1.5°C threshold.
The study attempted to evaluate five investigative approaches to examining the UK’s
existing buildings towards achieving the net-zero targets. The approaches investigated include
thermal imaging, in situ U-value testing, airtightness testing, energy assessment and
condensation risk analysis. Thermal imaging is a valuable tool for identifying heat loss, cold
spots and areas of trailing heat loss due to air leakage. It is a non-invasive method that
provides visual evidence of energy inefficiencies, allowing for proactive responses to improve
energy performance. In situ U-value testing is essential for measuring the thermal
transmission characteristics of building materials. It helps determine the efficiency of
insulation and informs retrofit decision-making. Airtightness testing helps identify air leakage
points and assesses the overall energy efficiency of buildings. It plays a crucial role in reducing
energy consumption and improving occupant comfort. Energy assessment provides a
comprehensive evaluation of energy usage in buildings, enabling informed decisions on energy
efficiency improvements. Condensation risk analysis helps prevent moisture-related issues,
such as surface and interstitial condensation, which can affect building performance and
occupant health. The study also examined the pros and cons of each investigative approach
and examined, through case studies, their practical implication for the building fabric.
Secondly, the findings from the various building performance evaluation approaches have
revealed several significant benefits. These include identifying and resolving building
temperature regulation issues, which is crucial for maintaining comfortable and energy-
efficient indoor environments. Moreover, implementing retrofits, such as solar panels, air
vents, insulation, heat recovery systems and air-sourced heat pumps, has significantly
improved thermal performance while reducing energy consumption, a key factor in energy
efficiency. The findings also underscore the negative impact of poor insulation quality and
artistry on the U-values of the buildings, emphasizing the importance of addressing
insulation issues. Additionally, the effectiveness of pulse technology in measuring
airtightness, even in extremely airtight houses, is highlighted, showing its value in assessing
and improving energy performance by identifying and addressing air leakage issues.
Furthermore, the successful use of high airflow and moisture management techniques
preserved the historic building fabric, demonstrating the balance between modernization
and heritage preservation. These findings are useful to building developers and owners.
Policymakers can incentivize and support these approaches through regulations, financial
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incentives and support programs to drive positive change in retrofit projects and achieve
energy efficiency goals.
Furthermore, this study’sfindings may have limited generalizability to diverse regions
with varying climates and construction practices. The effectiveness of retrofit interventions
may be context-dependent, considering building types and material differences. The study
may not have observed or analysed the full and lasting effects of the retrofit interventions it
investigated, as the study timeframe might have been relatively short. Additionally, the
study assumes that implementing the investigated approaches requires technical
knowledge and financial resources. However, this assumption may not be applicable
universally, as some individuals or entities may lack the necessary expertise or financial
means to carry out the proposed retrofit interventions. Additionally, the study might not
account for emerging technologies or unforeseen factors influencing sustainable retrofit
practices. While offering valuable insights, the study’s scope and applicability should be
considered within these limitations, emphasizing the need for ongoing research and
adaptability in the evolving field of energy-efficient retrofitting.
Also, continued research and innovation in investigating the existing building fabric are
vital. Further studies should focus on refining and developing new approaches to improve
the accuracy and efficiency of assessments. To validate retrofit interventions’effectiveness
and identify improvement areas, long-term performance monitoring of retrofitted buildings
is also necessary. By advancing knowledge in this field, researchers can inspire innovation
in sustainable retrofit practices and contribute to ongoing improvements in energy
efficiency.
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Corresponding author
Ebere Donatus Okonta can be contacted at: d.okonta@tees.ac.uk
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