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SAP Calculations

SAP Calculations

SAP Calculations are a requirement for all new dwellings and are also for conversion of use to a dwelling as well as some extensions, extensions that are over glazed will require SAP Calculations to show compliance, for more on over glazed extension please click here.

SAP stands for Standard Assessment Procedure, the calculation measures the proposed dwelling against a "notional dwelling" of the same size and shape as the proposed dwelling, to put it in layman terms the software we use duplicates the inputs we add into the software and assesses them against the same house with a specific set of U-Values, to see how this works here is a list of the target U-Values required to pass SAP today. The specific U-Values given are much lower than the maximum U-Values allowed for Part L 2013, as you can see below there is now a big gap between accepted maximum U-Values for Part L and the notional U-Values for the dwelling/s being assessed.


                             Part L Maximum U-Values                                       Notional Dwelling U-Values

Wall:                              0.30w/m2k                                                            0.18w/m2k

Floor:                             0.20w/m2k                                                            0.13w/m2k

Roof:                             0.20w/m2k                                                            0.13w/m2k

Party Wall:                     0.20w/m2k                                                            0.00w/m2k

Glazing                          2.00w/m2k                                                              1.4w/m2k

As you can see the notional dwelling requires much lower U-Values than building regulations allows, in earlier versions of SAP it was enough to comply with building regulations requirements, but it changed quite a lot in Part L 2013. 

Another requirement that was introduced into Part L 2013 was added to limit Thermal Bridging (Cold Bridging) as it is otherwise known, now the calculations require that all potential thermal bridging at junctions is accounted for as well a looking at options to reduce thermal bridging at the junctions by choosing to follow Accredited Construction Details (ACD) or Enhanced Construction Details (ECD) information about either of these methods and how to incorporate them into the dwelling design is readily available on the internet.

Air Tightness is also a factor in SAP 2012 (Part L 2013) with an allowable maximum of 10 air changes per hour, but, the notional dwelling has an Air Tightness of 5 air changes per hour, we would highly recommend using this figure as the target for all Air Testing as anything above is bound to fail SAP.

If you build new homes to the standards required by the "notional dwelling" you should have no problems getting a PASS from the SAP Assessment, although it doesn't mean that some elements cannot be slightly over the "notional U-Values" as SAP still works on an area weighted value, for example, if you build the external wall to a U-Value of 0.24w/m2k (which is easily achievable with modern insulation standards) but improve the insulation in the floor and roof thereby achieving a better U-Value than the notional then you dwelling should be able to scrape through the SAP Calculation, another element that has a big impact on the results is Air Tightness, reducing the figure that is targeted for Air Tightness means you can probably get away with U-Values above the notional standards elsewhere, we say probably because this is not always the case and depends on how close the design is to the notional standards.


25 July 2017


Domestic New Build, Commercial New Build, Domestic Conversion, Domestic Extension, Commercial Conversion, Commercial Extension, SAP Calculations, SAP Assessor, SAP Assessment, SAP Calculations in Lancashire, Who does SAP Calculations, Where can I get a SAP Calculation?
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