ESECT
The Woodknowledge Wales Early Stage Embodied Carbon Tool for Low Rise Housing
Step 1 of 13
1) Site – Nature of existing site and building form
2) Homes – Building fabric and materials
3) Services – Heating, hot water and renewable energy
Each section has a number of questions to respond to. As you work your way through the tool, click on the different response options for each question to see the upfront embodied carbon impact and carbon sequestration benefits* of the approach.
Once you have completed all of the questions, you will be given an overall upfront carbon impact rating (High-Medium-Low) and overall estimated upfront carbon figure (kgCO2e/m2) for your chosen approach. A summary of your responses is also provided alongside relevant guidance notes.
You can complete the questions within the tool by choosing the options which are most typical to your current approach to new housing development. Or, you could choose other options to see how an alternative approach could reduce your upfront carbon impacts.
Biogenic carbon products such as timber and natural insulations have the ability to sequester or ‘lock up’ carbon dioxide. Although this carbon may sometimes be released at the end of life due to combustion and/or decomposition, there are climate benefits of sequestering atmospheric carbon within long-lived biogenic carbon products which act as a ‘carbon store’. Delaying carbon emissions and increasing the size of carbon stores reduces climate impacts and reduces the possibility of reaching dangerous climate ‘tipping points’.
In lifecycle analysis, biogenic carbon figures are reported separately from the main upfront carbon figure. Please see this Woodknowledge Wales guidance for more information.
HOTSPOT! CARBON IMPACT – VERY HIGH
Building on existing woodlands can be a very high carbon approach and should be avoided where possible. Felling and clearing trees and roots can be a carbon intensive process. Efforts should be made to make sure the cleared trees can be utilised in a high value end use such as structural timber and have a long lifespan so they can continue to lock up carbon. There are also considerations around potential carbon released due to soil disturbances.
RECOMMENDATION – This is a very high carbon approach and should be avoided wherever possible. Consider developing on an alternative greenfield or brownfield site which does not require woodland felling.
CARBON IMPACT – MEDIUM
Greenfield sites are generally plots of land that have not been developed or built upon previously. This could include woodland (see adjacent), grassland, or agricultural land. Greenfield sites should not be confused with the “greenbelt” which is largely protected from development.
A benefit of greenfield over brownfield sites is that they are unlikely to suffer from contamination issues from past industrial uses and have minimal clearance and demolition requirements which can have high carbon impacts.
However, consideration should be given to the potential negative impacts on biodiversity, reduced availability of green space, and carbon released due to soil disturbances.
RECOMMENDATION – This is a better option than developing on a greenfield site with woodland or a highly contaminated brownfield site. However, steps should be taken to minimise carbon released from soil disturbances.
Brownfield sites comprise of land which has already been built upon or developed in some way, but is now available for another purpose. If there are minimal clearance or demolition requirements then this may be the lowest carbon approach.
Many brownfield sites are located in existing towns and cities which means that existing infrastructure such as transport and utilities may already be in place, reducing carbon impacts from new infrastructure development.
Often overlooked for brownfield sites, consideration should be given to protect biodiversity which can often be at higher levels compared to more ‘natural’ areas.
Although this tool is focussed on new build development, efforts should be made to refurbish existing buildings (retrofit) and reuse materials wherever possible, either on the same site or elsewhere. If the buildings must be cleared then efforts should be made to ‘deconstruct’ rather than demolish to allow as many materials to be reused as possible.
RECOMMENDATION – This is a better option than developing on a greenfield site with woodland or a highly contaminated brownfield site. However, steps should be taken to protect or enhance existing biodiversity and reuse existing materials/buildings wherever possible.
HOTSPOT! CARBON IMPACT – HIGH
Brownfield sites comprise of land which has already been built upon or developed in some way, but is now available for another purpose. If there are extensive clearance or demolition requirements then this may be a very high carbon approach. Demolition is a high carbon process due to the machinery requirements and transport emissions.
If the site is post-industrial it may be contaminated with e.g. chemicals, oils or asbestos which may require further processing and increase carbon impacts.
Although this tool is focussed on new build development, efforts should be made to refurbish existing buildings (retrofit) and reuse materials wherever possible, either on the same site or elsewhere. If the buildings must be cleared then efforts should be made to ‘deconstruct’ rather than demolish to allow as many materials to be reused as possible, taking into account potential contamination concerns.
RECOMMENDATION – This is a high carbon option due to the extensive clearance requirements, with possible further carbon impacts due to processing of contaminated areas. To reduce impacts, steps should be taken to reuse existing materials/buildings which are uncontaminated.
Compactness of building form/shape makes it easier to achieve energy efficiency standards such as Passivhaus, because the heat loss area of the building envelope is minimised in relation to the building’s volume. The lower the form factor the more efficient the building is from a heat loss perspective. However, building form can strongly influence embodied carbon too. A study* found that an increase in form factor of 0.5 is associated with an approximate increase in upfront carbon of 100 kg CO2e/m².
However, building form can strongly influence embodied carbon too. A study* found that an increase in form factor of 0.5 is associated with an approximate increase in upfront carbon of 100 kg CO2e/m².
Image credit: Adapted from image by Clara Koehler, Woodknowledge Wales
Please enter an estimated number in each box. The final box calculates your total number of dwellings. Use “0″ if you will not have any of that particular dwelling type on your development.
The average form factor of the proposed dwellings on your development is high (more than 2.5).
Improve the efficiency of the dwellings’ form to reduce upfront carbon impacts. Consider building fewer bungalows and detached homes, and more apartment blocks, terraced and semi-detached homes.
The average form factor of the proposed dwellings on your development is medium (between 2.0 – 2.5).
Improve the efficiency of the dwellings’ form to reduce upfront carbon impacts. Consider building more apartment blocks and terraced homes.
The average form factor of the proposed dwellings on your development is low (less than 2.0).
The dwellings on your development have efficient building form and are likely to include apartment blocks and terraced homes.
Note, this analysis is from a small sample and will be further validated from other embodied carbon studies in the near future. However, it provides a strong indication that form factor can be a useful metric for considering both operational energy use (heat loss) and embodied carbon.
Foundations & ground floors and external walls are usually two of the highest carbon elements and depending on material choices can make up around half of the building’s total upfront carbon footprint.
Roofs and windows usually have less of an impact but there are multiple alternative material options to choose from so may provide an “easy win” to reduce embodied carbon.
*Other elements modelled (listed in order of decreasing impact) are as follows: Foundations and ground floors; MEP; External walls; Party walls; Internal finishes; Roof; Internal walls; Windows; Internal floors; Glazed and main solid doors and staircase; Internal doors.
Estimated upfront carbon (A1-A5w) – 120 kgCO2e/m2
This option has the highest estimated upfront carbon with at least twice as much than options 3-5.
The vast majority of the upfront carbon in this approach (c.85%) is in the ground floor due to the volume of concrete used.
There are no additional carbon sequestration benefits from this approach.
RECOMMENDATION – This is a high carbon option. Depending on the site’s ground/soil conditions and the structural loads of the proposed buildings, consider a lower carbon option with less concrete, such as precast concrete or a suspended timber floor.
CARBON IMPACT – MEDIUM/HIGH
Estimated upfront carbon (A1-A5w) – 80 kgCO2e/m2
This is the option with the second highest upfront carbon. This option has an estimated 35% less upfront carbon than option 1 but has more than all of the other options.
The majority of the upfront carbon in this approach (c.70%) is in the ground floor due to the volume of concrete used.
RECOMMENDATION – Depending on the site’s ground/soil conditions and the structural loads of the proposed buildings, consider a lower carbon option with less concrete, such as precast concrete or a suspended timber floor.
Estimated upfront carbon (A1-A5w) – 60 kgCO2e/m2
This option has an estimated 50% less upfront carbon than option 1 and 25% less than option 2
The upfront carbon is fairly evenly split between the foundations and the ground floor but more so in the ground floor.
RECOMMENDATION – Depending on the site’s ground/soil conditions and the structural loads of the proposed buildings, consider a lower carbon option with less concrete, such as a suspended timber floor.
Estimated upfront carbon (A1-A5w) – 55 kgCO2e/m2
This is the option with the second lowest upfront carbon. This option has an estimated 55% less upfront carbon than option 1, 30% less than option 2 and 10% less than option 3.
The upfront carbon is fairly evenly split between the foundations and the ground floor.
The timber provides some additional carbon sequestration benefits, locking up an estimated 30 kgCO2e/m2, which is over one half of the total upfront carbon of the option.
RECOMMENDATION – This is a relatively low carbon option, but depending on the site’s ground/soil conditions and the structural loads of the proposed buildings, consider a suspended timber floor with sand and gravel solum capping instead of concrete to further reduce impacts.
CARBON IMPACT – LOW
Estimated upfront carbon (A1-A5w) – 45 kgCO2e/m2
This is the option with the lowest upfront carbon. This option has an estimated 65% less upfront carbon than option 1, 45% less than option 2, 25% less than option 3 and 20% less than option 4.
The timber provides some additional carbon sequestration benefits, locking up an estimated 30 kgCO2e/m2, which is two thirds of the total upfront carbon of the option.
RECOMMENDATION – This is a low carbon option, but depending on the site’s ground/soil conditions and the structural loads of the proposed buildings, consider pad or screw pile foundations, or use reclaimed materials to further reduce impacts.
Click the thumbnail below to download a detailed summary document with further information on the embodied carbon impacts of the build-ups.
It is important to note that factors such as ground/soil conditions and structural loads will dictate the foundation type and depth. The ability to choose a lower carbon foundation/ground floor option can therefore be limited.
However there are more opportunities for low-rise residential development where structural loads are less significant compared to medium/high-rise residential.
Other potential lower carbon options to consider which are not modelled above include pad and screw pile foundations, and the use of compacted aggregate to replace concete in foundations.
The upfront carbon figures referenced in this section have been modelled by Toby MacLean for Woodknowledge Wales.
The illustrations and detailed summary document have been created by Clara Koehler from Woodknowledge Wales.
The figures are estimated and have been rounded to the nearest 5 or 10 (except for in pages 3-7 in the detailed summary document).
The house type modelled was a c.80m2 (GIA) detached 2-storey house.
The modelling includes module A5 site wastage but excludes other site activities.
Soil conditions were estimated to be benign.
The foundation type was strip footing except for the raft ground floor option where the raft is the foundation but edge thickening of raft included under the upfront carbon of the foundations. Formwork for raft slab has been included but not formwork for strip footings.
Other assumptions as part of this modelling exercise included 400mm brick facing masonry cavity walls with 150mm PIR insulation: timber floor joists; blockwork for internal walls; pitched trussed rafter roof with clay tiles; aluminium framed double glazed windows (25% of external wall area).
The external wall build-ups modelled in this section all have U-values of 0.13 W/m2.K.
Estimated upfront carbon (A1-A5) – 100 kgCO2e/m2
This option has the highest estimated upfront carbon with at least 50% more than option 4 (I-beam).
The highest carbon elements within this build-up are: 1) cladding (brickwork), 2) wall structure (lightweight steel frame) and 3) insulation (mineral wool).
The specification for this build-up from outside to inside is brickwork, 50mm cavity, rainscreen slab, breather membrane, fibre cement sheathing board, mineral wool batts between studs, vapour control layer, plasterboard, plaster skim.
RECOMMENDATION – Consider switching the structure from steel to timber frame or I-beams, and the brickwork cladding to timber cladding or render to reduce the carbon impacts.
Estimated upfront carbon (A1-A5) – 80 kgCO2e/m2
This is the option with the second highest upfront carbon. This option has an estimated 20% less upfront carbon than option 1 (steel frame) but has slightly more than option 3 (timber frame) and around 20% more than option 4 (I-beam).
The highest carbon elements within this build-up are: 1) cladding (brickwork), 2) wall structure (block) and 3) insulation (PIR). The cladding makes up over 50% of the total upfront carbon. Consider switching to a lower carbon cladding material to reduce your carbon impacts.
The specification for this build-up from outside to inside is brickwork, 50mm cavity, PIR insulation boards, blockwork, plasterboard, plaster skim.
RECOMMENDATION – Consider switching the structure from blockwork to timber frame or I-beams; the insulation to a bio-based alternative, and the brickwork cladding to timber cladding or render to reduce the carbon impacts.
Estimated upfront carbon (A1-A5) – 75 kgCO2e/m2
This option has an estimated 25% less upfront carbon than option 1 (steel frame) and 5% less than option 2 (blockwork). However this option has slightly more upfront carbon than option 4 (I-beam).
The highest carbon elements within this build-up are: 1) cladding (brickwork), 2) insulation (PIR) and 3) internal lining. The cladding makes up over 50% of the total upfront carbon.
The timber frame provides some additional carbon sequestration benefits, locking up an estimated 25 kgCO2e/m2, which is one third of the total upfront carbon of the option. Further carbon could be sequestrated if a bio-based insulation such as woodfibre was used instead of PIR.
The specification for this build-up from outside to inside is brickwork, 50mm cavity, breather membrane, OSB, timber studs with PIR insulation and timber battens, insulated plasterboard, plaster skim.
RECOMMENDATION – Consider switching the insulation to a bio-based alternative, and the brickwork cladding to timber cladding or render to reduce the carbon impacts.
Estimated upfront carbon (A1-A5) – 65 kgCO2e/m2
This is the option with the lowest upfront carbon. This option has an estimated 35% less upfront carbon than option 1 (steel frame), 20% less than option 2 (blockwork) and 15% less than option 3 (timber frame).
The timber I-beam structure and cellulose insulation provide some strong additional carbon sequestration benefits, locking up an estimated 50 kgCO2e/m2, which is nearly as much as the total estimated upfront carbon.
RECOMMENDATION – This is the lowest upfront carbon option but consider switching the brickwork cladding to timber cladding or render to reduce the carbon impacts further.
Note – The biogenic carbon figures are provided as minus values for the purpose of this comparison chart but are displayed in life cycle analysis (LCA) as positive numbers.
The figures are estimated and have been rounded to the nearest 5 or 10 (except for in pages 3-6 in the detailed summary document).
For ease of comparison brickwork cladding has been specified in all four build-ups. It is noticeable that this material has high upfront carbon and alternative cladding options such as timber cladding or render should be considered where appropriate.
The roof build-ups modelled in this section all have a U-values of 0.11 W/m2.K.
HOTSPOT! CARBON IMPACT – MEDIUM/HIGH
Estimated upfront carbon (A1-A5) – 50 kgCO2e/m2
The range in upfront carbon figures for all options in this section are fairly close but this option has the highest upfront carbon.
This option provides some additional carbon sequestration benefits, locking up an estimated 35 kgCO2e/m2, which is two thirds of the total estimated upfront carbon. The majority of the biogenic carbon is in the roof structure, with some in the timber roofing battens. The PIR insulation does not provide any biogenic carbon benefits.
The highest carbon elements within this build-up are: 1) insulation (PIR), 2) cladding (concrete roof tiles) and 3) internal lining.
The specification for this build-up from outside to inside is concrete roof tiles, roofing battens and counter battens, breather membrane, timber rafters, PIR insulation, vapour control layer, insulated plasterboard, plaster skim.
RECOMMENDATION – This option has the highest upfront carbon and utilises PIR insulation which is made from fossil fuels. Consider switching to a renewable bio-based insulation or lower carbon roofing tile material such as natural slate tiles to reduce the carbon impacts of this option.
CARBON IMPACT – LOW/MEDIUM
Estimated upfront carbon (A1-A5) – 40 kgCO2e/m2
The range in upfront carbon figures for all options in this section are fairly close but this option has the second highest upfront carbon.
However, this option provides very strong additional carbon sequestration benefits, locking up an estimated 80 kgCO2e/m2, which is double the total estimated upfront carbon. The majority of the biogenic carbon is in the roof structure and the insulation, with some in the timber roofing battens.
The highest carbon elements within this build-up are: 1) cladding (concrete roof tiles), 2) roof structure (i-beams) and 3) insulation (cellulose).
The specification for this build-up from outside to inside is concrete roof tiles, roofing battens and counter battens, breather membrane, OSB, cellulose insulation between I-beams, OSB, vapour control layer, service void with timber battens, plasterboard, plaster skim.
RECOMMENDATION – The carbon sequestration benefits from this option are very significant and the highest upfront carbon element is the cladding. Consider switching to a lower carbon roofing tile material such as natural slate tiles to reduce the carbon impacts of this option.
Estimated upfront carbon (A1-A5) – 35 kgCO2e/m2
The range in upfront carbon figures for all options in this section are fairly close but this option has the lowest upfront carbon alongside Option 4 (Pitched cold roof with cellulose).
This option provides some additional carbon sequestration benefits, locking up an estimated 50 kgCO2e/m2, which is two thirds of the total estimated upfront carbon. Nearly all of the biogenic carbon is in the roof structure, with some in the timber roofing battens. The mineral wool insulation does not provide any biogenic carbon benefits.
The highest carbon elements within this build-up are: 1) cladding (concrete roof tiles), 2) roof structure (timber trusses) and 3) insulation (mineral wool).
The specification for this build-up from outside to inside is concrete roof tiles, roofing battens and counter battens, roofing felt, timber trusses, mineral wool batts, vapour control layer, plasterboard, plaster skim.
RECOMMENDATION – This option has the lowest upfront carbon but utilises mineral wool insulation which has some concerns in regard to its safety during handling and raw material extraction during production. Consider switching to a renewable bio-based insulation or lower carbon roofing tile material such as natural slate tiles to reduce the carbon impacts of this option.
The range in upfront carbon figures for all options in this section are fairly close but this option has the lowest upfront carbon alongside Option 3 (Pitched cold roof with mineral wool).
This option provides strong additional carbon sequestration benefits, locking up an estimated 65 kgCO2e/m2, which is nearly double the total estimated upfront carbon. The majority of the biogenic carbon is in the roof structure and the insulation, with some in the timber roofing battens.
The highest carbon elements within this build-up are: 1) insulation (cellulose), 2) cladding (concrete roof tiles) and 3) roof structure (timber trusses).
The specification for this build-up from outside to inside is concrete roof tiles, roofing battens and counter battens, roofing felt, timber trusses, cellulose insulation, vapour control layer, plasterboard, plaster skim.
RECOMMENDATION – Although the cellulose insulation is the highest carbon element in this option, alongside the timber roof structure, cellulose provides significant carbon sequestration and performance benefits which should be valued. Consider switching to a lower carbon roofing tile material such as natural slate tiles to reduce the carbon impacts of this option.
For ease of comparison concrete tiles have been specified in all four build-ups. It is noticeable that this material has high upfront carbon and alternative cladding options such as natural slate tiles should be considered where appropriate.
Estimated upfront carbon (A1-A5) – 155 kgCO2e/m2
This option has by far the highest upfront carbon.
RECOMMENDATION – Consider switching to a lower carbon option such as timber frame windows, which also provide carbon sequestration benefits.
Estimated upfront carbon (A1-A5) – 90 kgCO2e/m2
This option has the second highest upfront carbon but has over 40% less than Option 1 (Aluminium).
NOTE: uPVC windows are often the lowest cost option but are manufactured from petrochemicals and are therefore supporting the continued extraction of fossil fuels.
RECOMMENDATION – Consider switching to a lower carbon option such as timber frame windows, which are lower upfront carbon, provide carbon sequestration benefits, and are not manufactured from fossil fuels.
Estimated upfront carbon (A1-A5) – 70 kgCO2e/m2
Despite the use of aluminium this option has the second lowest upfront carbon – over 50% less then Option 1 (Aluminium).
This option provides additional carbon sequestration benefits, locking up an estimated 20 kgCO2e/m2.
RECOMMENDATION – Consider switching to a lower carbon option such as timber frame windows to reduce impacts further, whilst still retaining carbon sequestration benefits,.
Estimated upfront carbon (A1-A5) – 60 kgCO2e/m2
This option has the lowest upfront carbon – over 50% less than Option 1 (Aluminium).
This option provides additional carbon sequestration benefits, locking up an estimated 20 kgCO2e/m2, which is one third of the total upfront carbon.
RECOMMENDATION – This is the recommended option as it is both low upfront carbon and provides carbon sequestration benefits.
The upfront carbon figures referenced in this section have been modelled by Clara Koehler and Toby MacLean for Woodknowledge Wales.
The figures are estimated and represent averages taken from Environmental Product Declaration information at the time of writing (May 2025).
The calculations are per m2 of window area (not glazing area) and include window frames. All windows modelled are triple-glazed with an approximate U-Value of 0.8 W/m2K.
This section focusses on the upfront embodied carbon (A1-A5) of building services (including heating, hot water and ventilation) and renewable energy technologies.
Research into the embodied carbon impacts of building services is an emerging area and current data is variable. However, building services products and systems (e.g. gas boilers, heat pumps, mechanical ventilation units and ductwork) and renewable energy tech (e.g. photovoltaic panels and batteries) are often manufactured from high carbon materials including metals and plastics, so their embodied carbon impacts are important to consider.
Life cycle stages diagram.
Mechanical, electrical, and plumbing (MEP) equipment, which provide space heating and hot water in a home, can have a significant upfront carbon impact when first installed, and repeated embodied carbon impacts over the lifetime of the building when the equipment needs to be replaced.
The following question explores the upfront carbon impacts of four different domestic heating and hot water systems. The information provided is referenced from the TM65.1 Embodied carbon in building services: residential heating study, conducted by Elementa Consulting for CIBSE (2021). The figures referenced are for a notional new-build three-bed terraced house built to Passivhaus fabric performance (as this is the assumed trajectory for the performance of new homes).
The CIBSE study found that the embodied carbon impact associated with domestic heating systems can be quite high and could make up to an estimated 25% of the home’s total embodied carbon. The Essex Study made similar conclusions, estimating that MEP could make up to 23% of total upfront embodied carbon in a terraced home.
As a key point, it should be noted that to reduce operational carbon emissions and phase out the use of fossil fuels, the industry is improving the thermal performance of building fabric and moving away from the use of gas boilers. The next version of the UK building regulations is expected to ban the use of gas boilers in new homes and in Wales social housing providers must already ensure new homes have an EPC A rating by “not using fossil fuel fired boilers to provide domestic hot water and space heating”. Consequently, heat pumps are expected to become the dominant solution for new homes.
Commentary on the wider issues to consider is also provided, including the effects of improved building fabric on MEP sizing; refrigerant usage and ‘whole life carbon’ impacts of systems, which take into account operational emissions.
Estimated upfront carbon (A1-A5) – 19 kgCO2e/m2
This option has the highest upfront carbon. The study showed that the GSHP system has slightly higher upfront carbon than the ASHP and the gas boiler, and over twice as much upfront carbon than the direct electric approach.
The GSHP modelled as part of the TM65 study was fed by a horizontal ground loop, connected to a DHW store and a wet heating system with radiators.
Note: Heat pumps require the use of refrigerants which can have significant embodied carbon impacts across the building’s lifecycle, depending on the choice of refrigerant.
RECOMMENDATION – This option has the highest upfront carbon. Consider specifying an ASHP which may have lower ‘whole life’ carbon than direct electric (taking into account operational carbon). Prioritise the use of factory-sealed heat pumps and low global warming potential (GWP) refrigerants to minimise embodied carbon across the building’s lifecycle.
Estimated upfront carbon (A1-A5) – 17 kgCO2e/m2
This option has the second highest upfront carbon. The study showed that the ASHP system has slightly lower upfront carbon than the GSHP (around 10% lower), slightly more than the gas boiler, and over twice as much upfront carbon than the direct electric approach.
The ASHP modelled as part of the TM65 study was an air-to-water monoblock heat pump connected to a DHW store and a wet heating system with radiators.
RECOMMENDATION – Although this option is higher upfront carbon than the direct electric approach, when taking into account operational energy, the ASHP is estimated to have lower ‘whole life’ carbon, even when taking into account refrigerant leakage. Prioritise the use of factory-sealed heat pumps and low global warming potential (GWP) refrigerants to minimise embodied carbon across the building’s lifecycle.
Estimated upfront carbon (A1-A5) – 15 kgCO2e/m2
This option has the second lowest upfront carbon. The study showed that the gas boiler system has slightly lower upfront carbon than the ASHP (around 10% lower) and the GSHP (around 20% lower). However, it has over twice as much upfront carbon than the direct electric approach.
The gas boiler modelled as part of the TM65 study was a system gas boiler with a domestic hot water (DHW) store and a wet heating system with radiators. To allow for the installation of a heat pump in the future, the radiators were sized (larger than standard radiators typically used with a gas boiler) to operate at 45 °C flow and 35 °C return as heat pumps run at a lower temperature.
Gas boilers tend to be lighter than heat pumps and use material with less embodied carbon (more plastic, less aluminium), and heat pump systems require larger radiators. If a new heating system is installed with a gas boiler, it is best practice to futureproof the system by installing radiators that can operate at a lower flow temperature, so that the system can be easily switched to use a heat pump.
NOTE: Industry is beginning to phase out the use of fossil fuels and move away from the use of gas boilers. The next version of the UK building regulations is expected to ban the use of gas boilers in new homes.
RECOMMENDATION – This is a slightly lower upfront carbon option than heat pumps but is not a viable approach in the coming years as the installation of gas boilers is likely to be banned.
Estimated upfront carbon (A1-A5) – 7 kgCO2e/m2
This option has the lowest upfront carbon.
For the direct electric system modelled as part of the TM65 study, heating is provided through direct electric panel heaters and DHW is provided by an electric immersion heater in the DHW store.
NOTE: Direct electric systems are not the lowest operational carbon option and can have other operational implications such as high running costs and increased pressure on the electricity distribution grid.
RECOMMENDATION – Although this is the lowest upfront carbon option, the operational carbon impacts should also be considered before deciding on an approach.
Effects of building fabric efficiency
The TM65 study found that a house with a heat pump and ultra-low-energy fabric and a house with a gas boiler system and business-as-usual fabric, the upfront embodied carbon is found to be similar. The use of a heat pump usually requires radiator sizes to be increased (due to the low flow temperatures), which would usually increase the embodied carbon of the system. However, the better performance of the ultra-low- energy fabric reduces the generation capacity and the size and quantities of associated systems, thus the embodied carbon is not increased.
Whole life carbon impacts
When deciding on an MEP approach, to be able to make a truly meaningful decision, the ‘whole life carbon’ impacts of the various heating technologies need to be investigated, including the impacts of operational carbon emissions.
The TM65 study found that (using flat lifetime carbon factors and anticipating for continued decarbonisation of the electricity grid) over a 60 year lifecycle the direct electric and ASHP heating systems have similar whole life carbon emissions, whilst a gas boiler could contribute more than double that of the whole life carbon emissions of an ASHP.
When a ‘stepped carbon factor’ (essentially a more pragmatic vision of the grid decarbonising) is used, the study showed that the ASHP system has the lowest whole life carbon emissions, with a direct electric system having twice as many emissions and the gas boiler three times as many.
For more information on the TM65 study, please visit https://www.cibse.org/knowledge-research/knowledge-portal/tm651-embodied-carbon-in-building-services-residential-heating/.
A1-A4 upfront carbon figures are provided as A5 construction stage emissions are negligible in most MEP components.
Building mounted PV panels installed on the rooftops of new (and existing) homes represent “one of the quickest and lowest cost ways to meet net zero targets” according to the Essex Study. In addition, the next iteration of UK building regulations (Future Homes Standard 2025) is expected to mandate the use of rooftop solar in some capacity.
However, PV panels can be high embodied carbon.
One of the key components in PV panels is polysilicon which is energy intensive to mine and purify. Manufacturers should use renewable electricity to power their manufacturing processes in order to lower the embodied carbon impacts of their products.
Consider specifying PV panels which have been certified under standards such as the Global Electronics Council’s (GEC) ULCS frameworks or the ESMC’s Low Carbon Solar Module classification.
Although it is important to be aware of the embodied carbon impacts of PV and to specify products with lower impacts, the embodied carbon figures for PV are often excluded or reported separately from the full embodied carbon total for a building or development. This is due to PV being seen as a significant solution to meeting net zero operational carbon targets and the direct inclusion of their carbon impacts within a building or development level embodied carbon study could be detrimental to reducing operational carbon emissions.
Note – A series of options are not provided for this section and the information is provided as guidance.
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