SF40 our double thickness foil insulation is a favorite with professional loft converters and self builders alike, SF40 is combined with with 40mm foam backed plasterboard to give a U 0.18 is an LABC approved registered detail and meets current building regs the finished ceiling will be 90mm ( 3 1/2 inches) below the rafter
No insulation is required between rafters at all, great for time and cost saving and where rafters are small and the often essential ventilation gap is not lost.
SF40 can be used in a variety of ways, for those insulating under rafters using two layers of SF40 provides easy install and excellent results.
A standard SF40 2 layer ”Duet” detail is ;- Rafter, SF40, Batten, SF40, Batten, Plasterboard, this gives a U value of 0.147 , the finished ceiling will be 143mm mm ( 5 5/8th inches) below the rafter (see below picture figure B).
A couple of other details brought to our attention by experienced installers giving home owners higher specifications are U 0.135 this requires adding a layer of SFTV and another batten in the middle, the finished ceiling will be 156mm mm ( 6 3/8th inches) below the rafter (see below picture figure A). Or for space saving without the central middle low emissivity air gap its U 0.157 the finished ceiling will be 130mm mm ( 5 1/8th inches) below the rafter (see below picture figure C).
All 3 options give ease of install, add to air tightness, provide a radiant barrier which reduce solar gain in summer with improved thermal performance significantly better than current regs.
Download the full size 2D image here
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