EDITOR ’ S CHOICE building ’ s energy requirement are to be found in improving the fabric of the building itself – enhancing insulation and reducing thermal transmittance .
JACKON therefore very much welcomes the fact that the Government ’ s new Future Homes Standard is adopting a ‘ fabric first ’ approach in its drive to secure cuts in emissions of up to 80 %. This is set to be a key part of the construction industry ’ s framework going forward , underpinning the planned green recovery of the housebuilding market in particular .
Achieving the lowest possible U-value is also a key criteria for a building to gain Passivhaus certification , since it is a requirement to achieve a 75 % reduction in space heating requirements , compared to a standard UK new build .
Thermal transmittance , the U-value , is the rate of transfer of heat through a structure divided by the difference in temperature across that structure . The unit of measurement is W / m ² K . Workmanship and installation standards can strongly affect the thermal transmittance . If insulation is fitted poorly , with gaps and cold bridges , then the thermal transmittance can be considerably higher than desired . Thermal transmittance takes heat loss due to conduction , convection and radiation into account .
The U-value measurements can be calculated theoretically by considering the thermal transmittance of each layer of the building ’ s fabric , and there is a calculation method included in the relevant British Standard BS EN ISO 6946 : 2017 . This takes into account any mortar joints in the construction and also fixing components which have the potential to cause cold-bridging . Post-construction measurements using sensors are however the most robust way of assessing actual U-values , since they
are able to take workmanship into account , as well as the actual materials themselves .
The current regulations aim for a target U-value of 0.18 for external walls as a starting point to achieve a well-insulated building envelope . Insulating Concrete Formwork ( ICF ) constructions have been achieving this target easily for years in their basic configuration , with no “ add-ons ”, while other types of constructions have had to push their limits in terms of cavities , ties and expensive insulating material in order to achieve the existing levels of thermal performance .
The Future Homes Standard is up for further consultation , ahead of final implementation in 2025 , but it is clear it will be a requirement for housebuilders to build well-insulated homes , in which on-site renewable energy sources cannot be used to offset inadequate insulation at the construction phase . The Government is proposing target u-values of 0.15 for external walls and 0.11 for floors from 2025 , and there will be an initial uplift in Standards , coming into effect in June next year , via an amendment to Part L of the Building Regulations which sets the standards for the energy performance and carbon emissions of new and existing buildings .
JACKON is ready for these changes and is in fact arguing for them to be even more rigorous , by setting far more demanding air tightness targets . The new targets are not a problem , since JACKON ’ s THERMOMUR 350 ICF in its standard EPS configuration achieves a U-Value of 0.17 W / m2K . By using upgraded THERMOMUR 350 Super EPS that figure drops to 0.15 W / m2K . The next step up is THERMOMUR 450 with a U-Value of 0.11 W / m2K , which puts the building on course to become a Zero Carbon build .
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