New Notional Standards for New Homes
A lot of our clients are wondering why their designs are struggling to get through the latest version of Part L1A, the new notional standards for new build homes are considerably more stringent than in SAP 2010,
with the introduction of new FEE (Fabric Energy Efficiency) targets the government is hoping to encourage builders and developers to build more energy efficient homes but with a requirement of a fabric first approach.
What is Fabric First?
Fabric First simply means ensuring the fabric of the building is given more consideration than in old regulations, walls, floor and roof now have very tight limiting U-Value requirements which mean house builders and developers must ensure that the thermal fabric of a new home is at least up to the standards of the governments "Notional Dwelling" if you look at the information below you will see just how much better the fabric needs to be to comply with Part L 2013 against the requirements of current building regulations:
|Element||Building Regulations||Notional Dwelling|
|Roof||0.20 W/(m2K)||0.13 W/(m2K)|
|Wall||0.30 W/(m2K)||0.18 W/(m2K)|
|Floor||0.25 W/(m2K)||0.13 W/(m2K)|
|Party Wall||0.20 W/(m2K)||0.20 W/(m2K)|
|Swimming Pool Basin||0.25 W/(m2K)||0.00 W/(m2K)|
|Windows & Doors||2.00 W/(m2K)||1.4 W/(m2K)|
|Air Permeability||10.0m3/(h-m2) at 50Pa||5.0m3/(h-m2) at 50Pa|
As you can see, the notional requirements are considerably lower than building regulations standards, although there is some design flexibility, such as greatly improving the U-Value of an element to offset the U-Value of another, SAP Calculations still work on a area weighted or average U-Value, so getting an average over all the elements is still possible, once thing to be aware of though is it is no longer viable to simply bolt on a renewable energy source to pass the requirements of SAP.
So what can we do to make sure our buildings pass SAP Calculations?
The easiest method for ensuring your designs pass SAP is to make sure you have the best U-Values possible over all the elements, construction methods such as Brick & Block with full fill rockwool insulation are now so far wide of the requirements against the notional dwelling that it is almost impossible to make the calculations pass, if builders and developers wish to continue to use these construction methods the walls are going to have be a lot thicker, having looked at the calculations for a brick and block wall and trying to get the U-Value anywhere near to the notional dwelling standards we have found that the wall would need to be approximately 410mm thick, with 170mm Mineral Wool insulation based on Rockwool 32 or 420mm with Rockwool 34
So how can you help?
Here at Build Compliance Ltd we take a more holistic approach to passing Part L Calculations, we look at thermal bridging which can be a major reason why dwellings fail, we highly recommend using a minimum of accredited construction details and if possible using enhanced construction details