The other two cases did not appear to have a quoted U-value, however, the levels of insulation in these floors (70 mm of poly-isocyanurate and 100 mm of mineral wool) suggest that there should be no problem in achieving the Elemental requirement for these elements. One problem for the thermal performance of domestic floors was identified by NHBC for instances where the initial design of a floor has to be modified.
If the initial design specifies AAC blockwork in the foundations then modification of the foundations can alter the thermal performance and the need to add floor insulation as a compensatory measure can be overlooked by builders. For domestic constructions the main glazing used (where stated) was almost exclusively double glazing. U-values of windows in individual submissions to Property Valuation Services Control were higher than window U-values quoted in LANTAC type approval applications. Information on the overlap between the wall insulation and the window frame was often difficult to obtain accurately from the plans.
In the questionnaire survey consultees generally were of the view that many builders install double-glazing as standard and that almost all new dwellings have double-glazing. According to the consultees, there is some increase in the proportion of windows with PVC-U frames. One consultee mentioned that there is a greater use of lockable fasteners to allow opening lights to be left securely open and provide ventilation.
Particularly given that there are sometimes practical problems in fitting lintels and cills correctly. SAP submissions as part of the application for Building Control approval have been studied as part of this survey. Because the SAP need not be resubmitted until 5 days after completion of the new dwelling or dwellings, it was often not possible to obtain the SAP rating from the site. Out of the 98 applications for new dwellings examined, it was possible to examine the SAP calculation in 42 cases. This meant that they were having to go back to put right problems. As a solution to the problem NHBC suggested that builders should only use TRV’s in limited numbers per dwelling, and never in the same room as a room thermostat.