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Effect of orientation on the hygrothermal behaviour of a capillary active internal wall insulation system


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UK authorities are promoting energy efficiency schemes to improve the performance of buildings as a result of the high levels of energy consumption and consequent CO2 emissions. A quarter of these emissions are due to requirements for space heating. Installation of insulation is one of the most common alternatives to thermally improve buildings, especially on buildings built of solid masonry (~20 percent of the housing stock). However, the thermal improvement of buildings located in conservation areas, listed buildings, decorative façades, or traditional buildings could be only achieved through the use of internal wall insulation. Solid masonry walls with high surface water absorption coefficients have a higher dependence on external climate conditions (e.g. rain, solar radiation), which are likely to affect the performance of internal wall insulation. This paper examines the effect of walls orientation on the hygrothermal behaviour of an internally insulated 16th century building. External walls have been insulated with a capillary active system that allows moisture movement towards indoor environments. Sensors to monitor relative humidity and temperature between the existing brick wall and the insulation were installed in the north-facing and south-facing walls of the building. Both walls are exposed to the same internal environmental conditions (teaching area). The study showed that drying of the south-facing wall occurred faster than drying of the north-facing wall and that drying of the south-facing wall was enhanced by the effect of direct solar radiation.
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... The different exposure of walls to the local microclimate, including direct solar radiation and wind-driven rain, has an important influence on the building performance and wall conditions. Indeed, the hygrothermal performance of walls in a historic building can vary on a wall-by-wall basis, depending on their orientation [47]. Moreover, urban morphology influences the hygrothermal performance of historic walls; buildings in dense areas should not be treated in the same way as standalone buildings, especially regarding radiative exchange [48] and exposure to wind-driven rain. ...
... Relative humidity and temperature probes (and, less frequently, moisture content sensors) have been installed at various depths of insulated walls. This has been used in the assessment of the suitability of internal wall insulation systems for historic buildings (e.g., [47,76,[95][96][97][98][99][100]). ...
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Buildings of heritage significance due to their historical, architectural, or cultural value, here called historic buildings, constitute a large proportion of the building stock in many countries around the world. Improving the performance of such buildings is necessary to lower the carbon emissions of the stock, which generates around 40% of the overall emissions worldwide. In historic buildings, it is estimated that heat loss through external walls contributes significantly to the overall energy consumption, and is associated with poor thermal comfort and indoor air quality. Measures to improve the performance of walls of historic buildings require a balance between energy performance, indoor environmental quality, heritage significance, and technical compatibility. Appropriate wall measures are available, but the correct selection and implementation require an integrated process throughout assessment (planning), design, construction, and use. Despite the available knowledge, decision-makers often have limited access to robust information on tested retrofit measures, hindering the implementation of deep renovation. This paper provides an evidence-based approach on the steps required during assessment, design, and construction, and after retrofitting through a literature review. Moreover, it provides a review of possible measures for wall retrofit within the deep renovation of historic buildings, including their advantages and disadvantages and the required considerations based on context.
... The findings suggest that improved performance could be obtained by using insulation with higher water conductivity. Studies [6,9,10,14,16,[31][32][33][34][35] observed that good performance could be obtained by using diffusion-open capillary systems for internal retrofitting. In some of the studies the good performance that was observed could have been due either to exterior rain protection or a low internal moisture load. ...
... Although hydrophobisation appears to be an excellent solution [26], listed several limitations that must be considered, including problems with overall tightness and surface defects. Studies [12,33,39,46,52] have found that orientation was of great importance for the efficacy of internal insulation. High solar exposure on walls will contribute significant drying [18] but may also cause inward solar-driven vapour flow. ...
The present project investigated the hygrothermal performance and risk of mould growth in solid masonry walls fitted with three diffusion-open capillary active interior insulation systems installed in containers with a controlled indoor climate. The project was carried out as a large experimental study in two 40-feet reefer containers reconfigured with 24 holes (1 × 2 m), in which solid masonry walls with embedded wooden elements were installed. The focus of the study was on the conditions in the interface between the masonry and the interior insulation, and in the embedded wooden elements. The effect of exterior hydrophobisation was also investigated. Relative humidity and temperature were measured at several locations in the test walls over a period of four years. The findings indicate that exposed walls with interior insulation and high indoor RH performed poorly in terms of the risk of mould growth. Combined with exterior hydrophobisation against driving rain, the semi diffusion-tight insulation system performed better than the highly diffusion-open systems. Good performance was observed for the semi diffusion-tight polyurethane foam insulation with calcium silicate channels combined with exterior hydrophobisation. The effect of hydrophobisation varied with the orientation. Mould observations found no growth in the interface in most walls, probably because the high alkalinity of the adhesive mortars and scarce nutrition prevented growth. Growth was however found in some walls having low alkalinity and possibly available nutrition. Little correlation was found between on-site and modelled mould growth.
... Changes in climate factors are expected to accelerate the deterioration of masonry and detailing and undermine binders and coating on buildings [8,9]. Wall orientation will also make a difference and some building façades will require more attention than others, as south-facing walls dry out quicker than northfacing walls, the higher solar flux reducing relative humidity significantly [46]. ...
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This research aimed to provide the Welsh Government with measured and quantified climate vulnerabilities associated with housing building-fabric, including the potential financial cost of not planning for climate change. Wales’s climate is projected to become warmer but wetter and it is known that hygrothermal impacts can accelerate deterioration, leading to damp and, subsequently, a loss of thermal performance. A stressor-response methodology was applied, which assumes that the exogenous stressors of solar flux, precipitation, and humidity have a direct effect on building-fabric performance. The resultant stressor-response values equate to the quantitative impact that a specific stressor has on individual specific building elements, presented as an adjusted service life and associated costs. Results show a modest reduction in the service life of building materials due to increases in and changing patterns of precipitation and subsequent moisture ingress. Although modest, with 1.5 million dwellings in Wales, the impact is significant. Advocating regular maintenance and repair will not only reduce the risks associated with changing weather patterns, but also encourage energy efficiency by improving the thermal performance of the building envelope. This will reduce the risk of adverse climate related outcomes, increased vulnerability to climate change, now or in the future.
... D'Ayala et al. [99] monitored temperature and relative humidity in two historic walls and concluded that historical brick and mortar have different moisture absorption and desorption characteristics, even within the same building. Ultimately, the moisture content (MC) of historic walls with higher surface water absorption coefficients is more sensitive to exterior climate factors such as rain, wind, and solar radiation [100]. When high moisture conditions persist, damages like condensation, mold growth, wood decay, and frost damage may happen. ...
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Historic buildings account for more than one-quarter of Europe’s existing building stock and are going to be crucial in the achievement of future energy targets. Although a drastic reduction in carbon emissions would slow climate change, an alteration in the climate is already certain. Therefore, the impact of climate change on retrofitted historic buildings should be considered in terms of occupants’ comfort, heritage conservation, and energy performance. Inappropriate interventions might weaken the potential of traditional climate adaptive solutions, such as thermal mass and night cooling, leading to higher risks of overheating in a warming climate. Similarly, retrofit solutions will change the moisture dynamics of historic envelopes, which might lead to moisture damages when combined with more extreme precipitation events. This paper reviews recent literature that provides evidence of climate change’s impact on retrofitted buildings, reveals potential future risks, and thereby sheds light on new factors influencing the decision-making process in the retrofit of historic buildings.
... The diffusion-open capillary active systems allow the indoor moisture to diffuse in the outwards direction during the heating season, and then be redistributed back to the occupied zones by capillary actions as a mean to reduce the risk of mould growth inside the wall structure. Good hygrothermal performance for internal retrofitting solid masonry walls with diffusion-open capillary active systems have been observed in several studies including [6,7,15,[19][20][21][22][23][24][25], while other studies [26][27][28][29] found unacceptable relative humidity levels in the critical locations. The good performance in some of the aforementioned studies may be due to the combination of the diffusion-open capillary active systems with a low indoor moisture load and in some instances protection against Wind Driven Rain (WDR). ...
... Solar-driven vapour diffusion [7] occurs when a solid wall is exposed to solar radiation and liquid water is present in the wall; water evaporates and diffuses towards areas of lower vapour pressure. Solardriven vapour diffusion can be observed in solid walls in the UK, especially in walls with dark, porous surfaces exposed to direct solar radiation [8,9]. Solar-driven vapour diffusion can contribute to drying; however, moisture can accumulate in constructions with vapour tight interior finishes [10]. ...
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Solid wall buildings account for a quarter of the UK building stock and need to be thermally upgraded to meet national greenhouse gas emission targets. Internal wall insulation (IWI) is often the only option for the retrofit of solid walls, especially when they are of architectural or historical interest. However, IWI can lead to moisture accumulation within the existing wall, affecting the structural integrity of the building and the health of occupants. To avoid these issues, a thorough risk assessment is necessary. This paper presents a method for developing predictive meta-models that can be used for a fast probabilistic moisture risk assessment of IWI, considering both the uncertainty and variability of input variables. First, in a Monte Carlo analysis, the uncertainty and variability of inputs were propagated through hygrothermal simulations. Then, generalised additive models for location, scale and shape (GAMLSS) were used to describe the relationship between inputs and response variables of the Monte Carlo analysis. The key input variables were identified by a global sensitivity analysis - using the elementary effects method - and in model building. Two types of response variable were considered for the models: variables based on percentage values (e.g. maximum relative humidity) and dose-response relationships (e.g. mould index). The paper shows that both risk assessment models had a good predictive power, highlighting the suitability of the developed method for the moisture risk assessment of the internal insulation of solid walls.
... Case study 1 has two different woodfibre-based insulation systems on external walls with a south orientation; the sensors were located in walls of the living room (sensors L1, L2, L3), the bedroom (sensor B) and the staircase (sensors SC1, SC2, SC3, SC4). In case study 2, two walls of the same room were assessed: a north oriented wall (sensors N1, N2) and a south oriented wall (sensors S1, S2) [9]. In case study 3, walls in the kitchen, south oriented (sensor K) and the entrance, north oriented (sensor E), were assessed. ...
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The UK has pledged to reduce its carbon emissions by 80% by 2050. This translates into improving, among other measures, the energy efficiency of solid wall buildings, which requires the use of challenging measures such as internal wall insulation. Internal wall insulation can lead to moisture accumulation and mould growth at the interface between the insulation and the existing wall, if incorrectly designed and installed. Consequently, a thorough risk assessment is crucial for the design and specification of measures such as internal wall insulation. This paper presents the evaluation of mould growth models for the risk assessment of woodfibre internal wall insulation. The hygrothermal conditions within internally insulated solid walls were monitored and three models compared. The suitability of the models was assessed in relation to the risk of mould growth at the interface.
... Several studies on solar-driven vapour diffusion have been mainly conducted to document its occurrence and to identify the driving potentials for the mechanism (Derome and Carmeliet, 2010;Karagiozis, 2009). However, few have focused on the risk related to solar-driven vapour diffusion (Wellesley Smith, 2010), which has been found to occur in solid masonry walls exposed to wind-driven rain and solar radiation (Marincioni and Altamirano-Medina, 2014). ...
Conference Paper
Full-text available
In the UK, 20% of the building stock is subject to solar-driven vapour diffusion due to the un-rendered external surface of solid walls. Energy efficient interventions such as the installation of internal wall insulation can help to reduce greenhouse gases emissions and improve the thermal performance of those buildings. However, if the interventions are incorrectly designed, moisture accumulation may occur, which could be detrimental to the building and the health of its occupants. The moisture-related risk of such interventions is usually evaluated using hygrothermal simulations, however some of the input data required for the evaluation are not always suitable for the purpose; in particular, this is the case for external climate data. The aim of this study is to identify a suitable climate file for the risk assessment of internally insulated walls affected by solar-driven vapour diffusion. This paper presents an evaluation of the commonly used typical and near-extreme reference climate files for moisture risk assessment. Hygrothermal simulations were carried out for both types of climate files and 19 years of measured data. Results indicate that the near-extreme files under-represent the worst-case scenario and that the penetration of rainwater does not significantly affect the output of the hygrothermal simulations. A distribution of climate files was found to be more accurate and representative for the moisture risk assessment when considering solar-driven vapour diffusion.
Technical Report
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The present report summarized the outcomes of case studies developed within the RIBuild project. These case study buildings were evaluated regarding the documented damages and damage indicators, the location characteristics (weather conditions), the usage (indoor climate, type), historic constructions and retrofit constructions as well as specific aspects of constructive problems (e.g. joist ends, tightness). Findings from the project-internal case studies are supplemented with published case studies from 2003 and onwards. Furthermore, the design of the monitoring systems of these buildings is summarized and non-destructive on-site test for the characterization of these constructions and materials are presented.
The hypothesis investigated in this article is: it is possible to carry out moisture safe energy renovations in the old existing multi-storey buildings with heritage value and still save 50% of the building's energy consumption by use of existing technologies. A holistic energy renovation on an old multi-storey building with heritage value was carried out. Focus was given to energy-saving measures that would preserve the original architectural expression of the building, such as internal insulation. Comprehensive measurements were performed on the energy consumption before and after the renovation to document the obtained savings. Numerical simulations were validated with the measurements in order to explain the savings and to carry out parameter variations on the energy saving measures. Since internal insulation was applied the durability and robustness were investigated and measurements of the temperature and relative humidity were performed in the wooden beams-ends embedded in the masonry brick wall. A solution where the insulation was stopped 200 mm above the floor was investigated. This increased the heat flows through the wall compared to a fully insulated wall, and calculations showed that the difference in the space heating consumption was 3 kWh/m2/yr. The measurements showed the proposed solution should have no risk of moisture problems. The measured energy consumption was reduced with 47% whereas the theoretical reduction could be reduced with 39–61% depending on the room set-point temperature (20–24 °C).
Moisture atlas for building envelopes
  • P Häupl
  • H Fechner
Häupl P., Fechner H. et al. 2006. Moisture atlas for building envelopes. 3rd International Conference on Building Physics, Montreal, QC.
Long-term Measurement and Hygrothermal Simulation of an Interior Insulation Consisting of Reed Panels and Clay Plaster
  • P Wegerer
  • T Bednar
Wegerer P. & Bednar T. 2011. Long-term Measurement and Hygrothermal Simulation of an Interior Insulation Consisting of Reed Panels and Clay Plaster. 9th Nordic Symposium on Building Physics, Tampere, Finland.
Extra help where it is needed : a new Energy Company Obligation. © Crown copyright
  • Decc
DECC. 2011. Extra help where it is needed : a new Energy Company Obligation. © Crown copyright.