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Chapter 8
Non Repeating Thermal Bridges and the
Impact on Overall Heating Energy
Consumption in a Typical UK Home
Hasim Altan and Young Ki Kim
Abstract A non-repeating thermal bridge occurs at junctions when building
components such as a metal lintel crossing from the buildings’ interior to exterior
with a little or no intervening insulation, creating a ‘bridge’ for heat losses through
the external wall. In the UK, when considering a domestic building with standards
of the building regulation 2006, the proportion of heat losses due to non-repeating
thermal bridges is typically 10–15 %. This can rise up to 30 % in highly insulated
low energy buildings. Limiting thermal bridging will therefore become increasingly
important as more energy efficient buildings are being built due to more stringent
requirements by the current and future building regulations, and the endorsements
of higher levels by the Code for Sustainable Homes (CfSH) standard. The study has
undertaken dynamic computer simulations to calculate the impact on heating
energy consumption and to provide both cost and CO
2
benefit analysis for a typical
four bedroom terraced house with installation of Glass Reinforced Plastic (GRP)
lintels and conventional use of Steel lintels under London climate. Furthermore,
two-dimensional temperature and relative humidity distribution study has been
carried out to investigate the condensation risks, and the results are presented in
this paper based on energy performance where a better insulated home with GRP
lintels showed better performance levels in heating energy consumption, CO
2
emissions and overall energy bills. However, the most significant result of the
reductions was achieved by improving the building fabric. Moreover, the reduction
achieved from installation of GRP lintels has provided a further 10 % energy
demand reduction compared with the conventional Steel lintel use in the case
study home. With regard to the condensation risk and the two-dimensional study,
the paper has shown that the GRP lintel use would reduce non-repeating thermal
bridges significantly, particularly around junctions, and at the same time can help
keeping dry the area around the junctions. On the other hand, the Steel lintel use
would have high risks for condensation and again can cause further health impli-
cations with mould growth on surfaces.
H. Altan (*) • Y.K. Kim
Faculty of Engineering & IT, The British University in Dubai, Dubai International Academic
City, P.O. Box 345015, Dubai, United Arab Emirates
e-mail: hasim.altan@buid.ac.ae;kim19021@hanmail.net
©Springer International Publishing Switzerland 2014
I. Dincer et al. (eds.), Progress in Sustainable Energy Technologies Vol II:
Creating Sustainable Development, DOI 10.1007/978-3-319-07977-6_8
109
Keywords GRP lintel • Condensation risk • Heat losses • Thermal bridging
• Energy efficiency
8.1 Introduction
The Climate Change Act (2008) requires that by 2050 the UK’s annual carbon
dioxide (CO
2
) emissions should be reduced by 80 % compared to 1990 levels.
Home energy use is responsible for over a quarter of UK’s CO
2
emissions which
currently contribute to Climate Change. Therefore, the main aim is to reduce CO
2
emissions from all dwellings by an average of 80 % to help meeting a long term
goal [1].
The UK Government has committed for all new homes from 2016 to be net zero
carbon emitters which would help cutting down any future CO
2
emissions caused
by new build homes. On the other hand, considering the existing housing stock, the
government funded energy efficiency schemes in the UK with main objectives to
reduce fuel poverty and to minimise heating energy demand by several energy
efficiency measures such as cavity wall insulation, loft insulation, draught proofing,
and the option to improving a gas central heating system with energy efficiency
boiler replacement [2].
In a 2006 Building Regulation compliant dwelling in the UK (i.e. a representa-
tive 2006 compliant dwelling), the proportion of heat losses due to non-repeating
thermal bridges is typically 10–15 %. This can rise up to 30 % in better and highly
insulated low energy buildings [3]. The purpose of this study is to quantify the
impact on heating energy consumption when replacing conventional Steel lintels
with lass Reinforced Plastic (GRP) lintels within a given case study home, in this
case a typical four bedroom terraced house. Moreover, a comparison study has been
compiled with the consideration of various building standards such as ‘2006
Building Regulation’, ‘Best Practice’ and ‘Worst Case with No Insulation’. Fur-
thermore, the paper discusses the benefits with regard to energy bill and CO₂
emissions and payback analysis when the case of GRP lintels installed as replace-
ment to the common Steel lintels.
8.2 Energy Efficiency of UK Housing
8.2.1 Current Standards in Existing Dwellings
Figure 8.1 shows the average performance of the existing housing stock which is
band E rated (A to G band is based on the Standard Assessment Procedure (SAP)
rating score) [4] and there is still a poorly performing housing stock behind. These
are either F or G rated dwellings and it is where significant CO
2
emission cuts can
be made from the domestic building sector. If the UK Government’s saving target
110 H. Altan and Y.K. Kim
of overall 80 % cut in CO
2
emissions was to be made across the housing stock by
2050, the majority of dwellings will have to be an energy performance rated no
worse than band B, where again CO
2
emissions from most existing dwellings would
be no more than around 1.5 tonnes per year. This is estimated from an 80 % cut in
emissions from 160 million tonnes per year to no more than 32 million tonnes per
year, shared by all dwellings that would still be emitting CO
2
in 2050 [4,5]. In a
typical three-bedroom semi-detached house with 88.8 m
2
Total Floor Area (TFA),
household consumes 3,423 kWh/year, 3,412 kWh/year, 3,057 kWh/year and
1,314 kWh/year of energy for space heating, hot water, lighting and appliances,
and cooking respectively [5,6].
Improving thermal properties of building fabric and envelope through tightening
building regulations has been one of the ways forward for the country when tackling
energy efficiency in new build homes in the last 10 years. However, there are still
more to be done to improve energy efficiency in the existing housing stock in order
to meet the overall CO
2
emission reduction targets.
8.2.2 Thermal Bridging
Thermal bridges or cold bridges are weak points in the building envelope where
heat losses are worse than through the main building elements. The reason thermal
bridging has become important is very clear today. In the past, thermal bridges were
considered as insignificant causes for losses and therefore were not included in the
building regulations. Today however (and same applies for the past one decade), by
increasing the minimum requirements for the standards of building envelope,
i.e. U-value of building fabrics and the level of insulation through new and
tightened building regulations; thermal bridging has become more relevant and
must be considered. By improving the building fabric’s thermal property, the
majority of heat losses from buildings through thermal bridging and ventilation
G
percentage of dwellings in the stated range
20%
15%
10%
5%
0%
FABCDE
SAP ran
g
e
5 cr 6 to
less 10
11 to 16 to 21 to 26 to 31 to 36 to 41 to 46 to 51 to 56 to 61 to 66 to 71 to 76 to 81 to 86 to 91 to 96 to
15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Fig. 8.1 Performance of the UK’s existing housing stock [5]
8 Non Repeating Thermal Bridges and the Impact on Overall Heating Energy... 111
could be minimised. The Approved Document Part L 2010 points out that those
thermal bridges can account for more heat losses than all the walls put together [7].
To conserve energy and to prevent cold spots where condensation and mould can
form, thermal bridges need to be either completely eliminated or minimised [8]. It is
almost impossible to eliminate all thermal bridges, but the effect can be minimised
with careful detailing design and construction. Figure 8.2 shows thermal bridging
and air infiltration at and around lintels including an Infrared (IR) image of a steel
lintel over a window opening.
8.2.3 Airtightness
Air leakage is defined as the flow of air through gaps and cracks in the building
fabric. Uncontrolled air leakage increases the amount of heat loss as warm air is
displaced through the envelope by colder air from outside [8–10]. Air leakage of
warm damp air through the building structure can also lead to condensation within
the fabric (interstitial condensation), which reduces insulation performance and
causes fabric deterioration. The air permeability of a building can be determined by
means of a pressure test. In terms of Building Regulation Part L for new dwellings
[11], it is indicated that reasonable provision for airtightness is to achieve a pressure
test result of no worse than 10 m
3
/(h m
2
) @ 50 Pa. Current good practice for energy
efficient dwellings includes achieving airtightness of 7 m
3
/(h m
2
) @ 50 Pa and best
practice is 4 m
3
/(h m
2
) @ 50 Pa with heat recovery unit [11]. Table 8.1 shows the
various air permeability standards. In 1998, the Building Research Establishment
(BRE) carried out air pressure test to obtain the heating season mean background
infiltration rate of a typical UK dwelling and it was 0.65 ach
1
. From this study,
replacing old leaky windows with modern sealed windows would reduce the
background infiltration rate by 0.23 ach
1
[12]. Furthermore, replacing windows
while simultaneously changing the existing lintels to GRP lintels together with the
use of airtight tapes around the openings and the lintels would help to improve
airtightness of the dwelling as well as to provide a better thermal envelope.
9.5 °C
8
6
4
2
1.5
Fig. 8.2 Common thermal bridges and air infiltration at and around lintels
112 H. Altan and Y.K. Kim
8.2.4 GRP Lintel
A GRP lintel is made of glass reinforced plastic which makes it high load bearing
yet lightweight and has a profile as shown in Fig. 8.3 and a mass of 5.96 kg/m. It is
suitable for use in external or internal walls of 100 mm brick/block work with a 75–
100 mm cavity, and clear openings of between 400 and 1,700 mm, to support walls,
floors, roofs, or a combination of these structures, above window or door
openings [13].
Table 8.2 shows the thermal characteristics of a GRP lintel comparing with a
conventional Steel lintel. GRP lintels have a very low heat transmitter rate. Thus, it
is possible to reduce the effect of thermal bridging by replacing a conventional Steel
Table 8.1 Air permeability standards
Building standards
Maximum air permeability [m
3
/(h m
2
)@
50 Pa]
AD L1A of Building Regulations (2010) 10 (0.5 ach
1
)
EST (naturally ventilated) 7 (0.35 ach
1
)
EST (mechanically ventilated with heat recovery
unit)
4 (0.2 ach
1
)
The Netherlands 6 (0.3 ach
1
)
Germany (air changes per hour at 50 Pa) 1.8 ~ 3.8 (n50 h
1
)
PassivHaus <1 (0.1 ach
1
)
Super E (Canada) (air changes per hour at 50 Pa) 1.5 (0.075 h
1
)
Note: Energy Saving Trust (EST), Approved Document L1A (AD L1A)
Fig. 8.3 GRP lintel profile and exterior
Table 8.2 Thermal characteristics of a GRP lintel
Lintel type CO
2
emissions (kg CO
2
per kg) U-value (W/m
2
K)
Linear thermal bridge
Heat loss, ΨPsi value
(W/m K)
Steel Lintel 1.91 2.94
a
0.287
GRP Lintel 5.5 0.833 0.04
a
Minimum R-value for the lintel is 0.34 m
2
K/W [13]
8 Non Repeating Thermal Bridges and the Impact on Overall Heating Energy... 113
lintel with a GRP lintel. The thermal profile of a GRP lintel is also adopted further
in energy simulation analysis.
8.3 Methodology
8.3.1 Case Study Home and Building Standards
In order to carry out simulation studies, a four bedroom terraced house with a TFA
of around 140 m
2
has been modelled within a dynamic computer software package,
in this case DesignBuilder [14]. The properties are of timber frame construction and
built using off-site manufacturing techniques. The internal panelling consists of a
vapour permeable paper based membrane, wrapped and sealed into door and
window openings with cellulose fibre insulation also for sound reduction in
partitioning wall units. Total external walls are built up to achieve a U-value of
0.21 W/m
2
K and a minimum SAP rating of 100 (B rated) [4].
The case study house was adopted with three different building standards which
are as follows: ‘No Insulation’, ‘2006 Building Regulation’ and ‘Best Practice’.
Table 8.3 and Fig. 8.4 provide more details on building fabric (thermal character-
istics) and floor plans.
8.3.2 Energy Bill and Carbon Dioxide Emissions
As part of the computer simulations studies, the DesignBuilder [14] software has
been used for calculations of the heating energy consumption based on a certain
geographical location and climatic data, in this case London. In the simulations,
both the CO
2
emissions and the energy bills have been calculated with values of
unit price and CO
2
emissions rate referenced from SAP 2009 [4] as shown in
Table 8.4). From the energy bills calculated, the annual savings have been esti-
mated with simplified payback periods for each by also calculating the installation
of GRP lintels through different building standards.
Table 8.3 Adopted building standards (U-value and ach
1
)
Unit No insulation 2006 Building regulation Best practice Case study home
Wall 2.071 0.35 0.25 0.23
Floor 1.463 0.25 0.15 0.1
Roof 1.54 (flat)
2.93 (pitch)
0.25 (flat)
0.16 (pitch)
0.15 0.14
Window/door 6.121 1.978 1.978 2.26
Air infiltration 1 0.5 0.3 0.5
114 H. Altan and Y.K. Kim
8.4 Results and Discussion
8.4.1 Energy Consumption
Figure 8.5 shows the heating energy consumption compared with the worst
case scenario with GRP lintels installed through different building standards.
Living Room
Bedroom Bedroom
Bedroom Bedroom
g
round-floor first-floor
Kitchen
Fig. 8.4 Case study home
(four bedroom terraced
house) floor plans
Table 8.4 Unit price and CO
2
emissions from energy sources in SAP 2009 [4]
Unit Unit price (p/kWh) CO
2
emissions (kg/kWh)
Gas 3.10 0.198
Fig. 8.5 Heating energy consumption and reduction breakdown
8 Non Repeating Thermal Bridges and the Impact on Overall Heating Energy... 115
The simulation results have indicated that a GRP lintel with a high insulation level
of building standard shows better performance of heating energy consumption
providing better energy efficiency. Using GRP lintels within a non-insulated
house due to thermal bridging through building fabric and junctions reduces heating
energy consumption by 652 kWh/year. However, introducing insulation into the
building fabric would significantly improve the heating energy savings compared
with the worst case scenario, and the savings are estimated as 54,052 kWh/year,
60,147 kWh/year and 62,350 kWh/year for different standards as follows: ‘2006
Building Regulation with GRP Lintels’, ‘Best Practice with GRP Lintels’ and ‘Case
Study Home with GRP Lintels’ respectively. In summary, it can be seen that the
majority of the reduction is made by increasing insulation levels in the building
fabric. However, the results also show that increasing thermal properties of the
building fabric with the use of a GRP lintel helps to further improve the heating
energy reduction.
The best case scenario in this case is the ‘Case Study Home with the GRP
lintels’, showing savings of a further 10 % of heating energy consumption, which
also provided a clear view on why a highly insulated dwelling should consider
reducing its thermal bridges. Well detailed and constructed buildings would there-
fore result in huge reductions in heating energy consumption with additional
reductions obtainable from eliminating thermal bridges.
8.4.2 Cost and Carbon Dioxide Analysis
Figures 8.6 and 8.7 show the overall energy bills by also using the GRP lintels
together with CO
2
emissions from heating energy savings. After introducing insu-
lation into the building fabric, there are significant savings in energy bills as
Fig. 8.6 Overall energy bill and CO
2
savings
116 H. Altan and Y.K. Kim
expected that can be made and again reduction in associated CO
2
emissions. As
mentioned above, most of the reductions were made by increasing the building
fabric’s thermal properties and in addition, the GRP lintel installation has contrib-
uted to further reduction in heating energy bills and associated CO
2
emissions as
shown in Fig. 8.7.
Figure 8.7 shows how the impact of GRP lintels on energy bills and CO
2
emissions through savings using different building standards. Again, the better
the insulation levels are with GRP lintels the better the performance results are in
terms of overall savings in energy bills and CO
2
emissions. However, the savings
between ‘2006 Building Regulation’ and ‘Best Practice’ cases are almost insignif-
icant, and therefore further studies should be undertaken to investigate the likely
reasons behind this.
8.4.3 Payback Analysis
The payback period for the GRP lintel installation has been calculated within the
case study home considering various building standards which was also based on
heating energy bills as shown in Table 8.5. Total length of GRP lintels within a
selected dwelling is about 13.3 m and the unit price of a GRP lintel is provided by
the supplier company [13]. The total difference in unit price between the supply of a
GRP lintel and a Steel lintel is around £400 per house (the price is excluding labour
charge and transportation). Thus, the best payback period is estimated in the case
study home with GRP lintels as around 10.2 years and in the worst case scenario as
almost 20 years. The payback periods shown in Table 8.5 represents the additional
values for installing GRP lintels in new build homes instead of Steel lintels.
Table 8.6 shows typical payback periods for energy efficiency measures in a case
study house. Most of these improvements are allowances received through grants
from either the UK government or energy suppliers, and as a result, the payback
periods are much shorter. However, these measures should not be compared
Fig. 8.7 Energy bill and CO
2
savings by GRP lintels
8 Non Repeating Thermal Bridges and the Impact on Overall Heating Energy... 117
directly with the GRP lintel installation as lintel is more directly related to con-
struction detailing rather than energy efficiency.
8.4.4 Temperature and Humidity Distribution Analysis
Two-dimensional temperature (C) and relative humidity (%) profiles through the
GRP lintel under winter conditions have been simulated. The boundary conditions
are as follows: Temperatures for internal and external conditions are adopted as
20 C and 5 C; relative humidity levels for internal and external conditions are
adopted as 55 % and 84 % respectively. Figure 8.8 illustrates the results, in this case
temperature distribution as shown on the left and relative humidity distribution as
shown on the right. From the results (see Fig. 8.8d), it can be concluded that filling
the box cavity of a GRP lintel would not be recommended and even a GRP lintel
filled with insulation gives a negative impact on the surface temperature distribu-
tions, it would have no effect on the reduction of thermal bridging. On the other
hand, the Steel lintel shows that heat losses through a Steel lintel are significant and
therefore, there is a very high likely risk of condensation around internal surface of
window frames and also at the attached internal wall surfaces. This also provides
Table 8.5 Payback periods
Case
Reduction
(kWh/year)
Energy bill
savings (£/year)
a
Payback period
(year)
b
Worst case scenario with GRP lintels 652 20.2 19.8
2006 Building regulation with GRP lintels 1022 31.7 12.6
Best practice with GRP lintels 1049 32.5 12.3
Case study home with GRP lintels 1267 39.3 10.2
a
Unit price is 3.10 p/kWh for gas [4]
b
Total length of the GRP lintel used is about 13.3 m required for installation in a case study home
and the total price for is around £532 [13]
Table 8.6 Typical payback periods in home improvement (as part of energy efficiency)
Improvement Installation cost
a
Annual savings Payback period
Hot water tank insulation £12 £40 5 months
Hot water pipe insulation £10 £10 1 year
Loft insulation (270 mm) £199 £205 Less than 1 year
Suspended timber floor insulation £90 (DIY) £50 2 years
Cavity wall insulation £149 £160 Less than 1 year
Draught proofing £90 (DIY) £30 3 years
Solar PVs £11,700 £1,200 Around 10 years
Solar thermal £4,000 £650 Around 6 years
a
Costs are average values based on UK government grants [5]
118 H. Altan and Y.K. Kim
Fig. 8.8 Two-dimensional temperature and humidity distributions. (a) Steel lintel, (b) steel lintel
filled with insulation, (c) GRP lintel, (d) GRP lintel filled with insulation
8 Non Repeating Thermal Bridges and the Impact on Overall Heating Energy... 119
further impact on the health of occupants and may likely to cause problems due to
mould growth on indoor surfaces.
The red circles show where the thermal bridges occurred and where there are
risks of condensation. An especially high risk of condensation could occur between
a window frame and a lintel where the surface temperature is around 13 C and the
relative humidity level is over 90 %. On the contrary, the window with a GRP lintel
shows better performance as it almost eliminates of thermal bridging. The internal
wall surface temperature is almost the same with room temperatures and humidity
levels that are within an acceptable range without any condensation problems. To
prevent interstitial condensation between the external brick and the cavity insula-
tion layer, vapour barriers should be installed.
8.5 Conclusions
The studies were carried out to investigate the impact of Fulbrook Glass Reinforced
Plastic (GRP) lintel [13] on heating energy consumption. In terms of energy
consumption, a better insulated home with GRP lintels shows a better performance
in terms of heating energy consumption, CO
2
emissions and overall energy bills.
However, the most significant result of these reductions would be achieved through
the improvement of building fabric’s thermal property. Moreover, the reduction
achieved from the GRP lintel installation should not be ignored, especially as
demonstrated in the best case scenario, i.e. in the case study home with GRP lintels,
which gave a further 10 % energy demand reduction compared with the other
scenario where there was no GRP lintel installation in the case study home as shown
in Fig. 8.9.
Fig. 8.9 Heating energy savings due to GRP lintel incorporated with different building standards
120 H. Altan and Y.K. Kim
The two-dimensional temperature and humidity distribution studies showed that
the GRP lintel installation could reduce thermal bridges significantly around junc-
tions. In terms of the condensation risk, under typical winter conditions, the Steel
lintel installation would have high risks for condensation and again may cause
further health implications with mould growth on indoor surfaces. On the other
hand, the GRP lintel installation shows better results in terms of minimising heat
losses at and around lintel profiles, and at the same time helps keeping dry the area
around the junctions. Therefore, the condensation risks would be very low, much
lower than a conventional Steel lintel.
The study has undertaken dynamic computer simulations to calculate heating
energy consumption and to provide cost and CO
2
analysis for the GRP lintel
installation. The results have given some ideas for energy efficiency as well as
cost benefit analysis for the GRP lintel use by also considering various different
building standards. However, without a post occupancy monitoring of a live project
and a case study home with the GRP installation, it is difficult to cross-check the
results obtained in the simulations and to also validate them. Therefore, further
studies are planned for the near future.
Acknowledgements The authors would like to thank Chris Sullivan (Material Edge Ltd) for
providing information about a GRP lintel (The Litel
®
) and Prof. Dr. Jitka Mohelnikova at Brno
University of Technology – Faculty of Civil Engineering (VUT FAST Brno) for her input and
advice. The authors would also like to thank the Building Environments Analysis Unit (BEAU)
Research Centre (2007–2013) at the University of Sheffield and the British government funding
Engineering and Physical Sciences Research Council (EPSRC) for making this research collab-
oration possible.
References
1. HM Treasury (2006) Pre-budget report 2006, investing in Britain’s potential: building our
long-term future. HM Treasury, London
2. DECC (2011) Annual report on fuel poverty statistics 2011. National Statistics, Department of
Energy & Climate Change (DECC)
3. LSI. Low carbon housing, learning zone, Leeds Metropolitan University, Leeds Sustainability
Institute (LSI). http://www.leedsmet.ac.uk/teaching/vsite/low_carbon_housing/thermal_bridg
ing/introduction/index.htm. Accessed on 24 Feb 2012
4. BRE (2010) The government’s standard assessment procedure for energy rating of dwellings
2009 edition. Building Research Establishment (BRE), Garston, Watford
5. EST (2010) CE317—Domestic low and zero carbon technologies: technical and practical
integration in housing. UK. Energy Saving Trust (EST)
6. CLG (2009) English Housing Condition Survey 2007. Annual report, Communities and Local
Government (CLG)
7. NHBC. Approved Document Part L 2010: Special Edition. Technical Extra, September 2011,
Issue 03, National House Building Council (NHBC). http://www.nhbc.co.uk/
NHBCPublications/LiteratureLibrary/Technical/TechnicalExtra/filedownload,44601,en.pdf.
Accessed 24 Feb 2012
8 Non Repeating Thermal Bridges and the Impact on Overall Heating Energy... 121
8. Government of Ireland (2008) Limiting thermal bridging and air infiltration: acceptable
construction details. Report by Department of the Environment, Community and Local
Government, HomeBond, Sustainable Energy Ireland (SEI), July 2008
9. EST (2005) Guide GPG224—improving airtightness in dwellings. Energy Saving Trust (EST)
10. BRE (2006) BRE Information Paper IP 1/06—assessing the effects of thermal bridging at
junctions and around openings. Building Research Establishment (BRE), Garston, Watford
11. HM Government (2010) The Building Regulation 2010: conservation of fuel and power in new
dwellings. Approved Document Part L1A. HM Government, London
12. Stephen RK (1998) Airtightness in UK dwellings: BRE’s test results and their significance.
BRE Report 359. Building Research Establishment, Garston, Watford
13. Litel. LITEL®.http://litel.co.uk/. Accessed 24 Feb 2012
14. DesignBuilder. DesignBuilder software. DesignBuilder Software Ltd. http://www.
designbuilder.co.uk/. Accessed 24 Feb 2012
122 H. Altan and Y.K. Kim
