SAP2012 was unveiled under a cloak of darkness and without fanfare at the start of June. Until Part L is confirmed and released in England and Wales (and the updated Section 6 in Scotland), the SAP methodology will not be used, so we’ve got a few months to understand what’s changed, and how that may impact next year’s building projects.
Awareness about thermal bridging in new homes rose sharply when SAP2009 was launched, as from this point developer’s needed to provide evidence that the junctions of their buildings (such as insulation breaks at corners, around windows and where the wall meets the roof) where constructed in line with approved information.
The most common set of figures to use is Accredited Construction Details – the instructions for how to build to this standard are free to download from Planning Portal.
Houses which were built without evidence of good thermal bridging details suffered with higher emission rates, and were much more unlikely to show compliance with the 2010 Target Emission Rate.
So, what is thermal bridging?
At every junction in a building, there is the risk of creating a cold spot. This is where there is a break in insulation, which means heat can escape from the building. If these junctions are not insulated properly, the emission rate of the building is seen to be much higher.
To prove a building is being constructed to best practice, there are approved ways of construction these junctions.
The current SAP is able to look at 23 different junction areas. All junctions involve breaks in a heat loss wall, and include areas such as where the wall meets the floor or roof, where there is a break due to a party wall, and where there is a corner in the building.
The length of each junction is assessed, so the more junctions you build to an approved standard, and the fewer junctions you have in the first place, the better result you will get on SAP.
When the new SAP is launched, 10 new wall junctions will be added, including balcony junctions, heat loss upper floors (such as overhangs) and walls in basements.
But on top of this, roof junctions are being added for the first time. Nine new junctions will measure the thermal bridging where roof insulation is interrupted by rooflights, ridges and where sloping insulation meets horizontal insulation.
For a good SAP result, always use approved junction details, and design your building to keep non-essential thermal bridges to a minimum.