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Flat Roof insulation advice

Posted by Deborah Watson, on
We have a flat-roof extension over 2 storeys which is a concrete slab covered with traditional felt and measures approx 2.5 x 5.0m. There are two issues with it that we wish to solve. The first is the more immediate as there is a leak where this roof adjoins the main part of the building and is causing damp in the two walls, one of which is cob. Although we have had a short term fix applied we have no idea yet if this has stopped the problem as there has been no rain but either way a long-term solution is required and this is probably best tackled as part of solving the second problem. We also wish to insulate this roof and have had conflicting advice on whether this is possible to do on the outside (if so we would then want the new structure to be covered in a more resilient coating such as EPDM). There is an small lip of approx 70mm depth between the felt and the raised edge of the roof's perimeter. Should it be insulated on the inside or outside?
Jesse Clarke

Jesse Clarke

Hi Deborah, This can be insulated from the outside using kingspan and then covered in EPDM. It is what is referred to as a warm deck roof. There needs to be breathable layer installed also in order to counter any condensation. Our details are on the internet at Max Roofings website (w. maxroofing. co. uk). I don't know where you are but we are based in the west yorkshire area and cover Leeds, Bradford, Wakefield, Huddersfield, Halifax, Burnley, Blackburn and all surrounding areas. We can also travel further if required. If you think we can help then please feel free to look us up and give me a call. Jesse.
Michael Nixon

Michael Nixon

All flat roofs should now be insulated under PartL 1b to current building regs. In the past on these types of roof we use the following specification. 4mm torch on vapour barrier, 150mm rigid polyurethane insulation boards, Firestone EPDM and UPVC fascias to the perimeter. Unless there are design considerations no flat roof should be insulated from the inside!

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