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SAP 2005 has two sets of y-values:
y=0.15 is SAP default for all forms of construction in the absence of any information about the junction details, and;
y=0.08 can be used where details can be shown to be consistent with published junction details known as "Accredited Construction Details" (ACDs) for masonry, timber frame and steel frame buildings.
In 2010, SAP 2009 will no longer permit the use of y=0.08 for accredited details. Instead a set of Ψ-values published in Appendix K of the SAP Specification will have to be applied to all junctions, and the results summed to calculate the total thermal bridge heat loss for the building.
In the knowledge that Part L of the UK building regulations were being revised, Prestoplan has undertaken third party thermographic junction modelling of 11 critical junctions in the PresWall Plus system. These certified values can be used with confidence delivering a significantly lower Ψ-value than the old ACDs. This maximises credit points and therefore reduces any dependency on renewable technologies.


