DIYmadDAD Posted February 21, 2021 Share Posted February 21, 2021 I'm planning a loft conversion and a builder has advised me to replace the existing roofing felt with a breathable type to comply with building regs. My original intention was to insulate the roof between & over rafters with a 50mm ventilated cavity under the existing felt. I know a breathable felt is required for new-builds but I've not heard of a need to replace the felt during renovation before. The loft is ventilated and house built 2006. I'd welcome some other opinions. TIA Link to comment Share on other sites More sharing options...
nod Posted February 22, 2021 Share Posted February 22, 2021 If he’s going to strip the roof tiles as art of your conversion Its not a big or expensive job to replace the felt Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 22, 2021 Share Posted February 22, 2021 As nod said, why are you not taking the whole roof off and re new it all. Link to comment Share on other sites More sharing options...
tonyshouse Posted February 22, 2021 Share Posted February 22, 2021 There are hundreds of thousands of loft conversions where this has not been done and we don’t hear of problems, why waste the effort Link to comment Share on other sites More sharing options...
Onoff Posted February 22, 2021 Share Posted February 22, 2021 (edited) 40 minutes ago, tonyshouse said: There are hundreds of thousands of loft conversions where this has not been done and we don’t hear of problems, why waste the effort I think that traditional, bitumen based, string reinforced roofing felt under tiles, has a lifespan of approx 30 years?I can't imagine in 2006 they used that though? (I know mine done in 1987 is becoming very brittle). Maybe the company doing the loft extension is dubious of the original work. At least if they renew the lot and it leaks then there's only one company to blame! Edited February 22, 2021 by Onoff 1 Link to comment Share on other sites More sharing options...
joe90 Posted February 22, 2021 Share Posted February 22, 2021 If the felt is well installed, in good Nick and does not need to be disturbed then why (if you are leaving a ventilated space ). Link to comment Share on other sites More sharing options...
DIYmadDAD Posted February 22, 2021 Author Share Posted February 22, 2021 Thanks guys. It seems that the consensus here and elsewhere that it's a very expensive 'nice to have'. The real question is if anyone has had experience of building control insisting on the replacement of standard felt with a breathable type? Link to comment Share on other sites More sharing options...
Onoff Posted February 22, 2021 Share Posted February 22, 2021 If you're replacing more than 25% of the roof covering haven't you got to "upgrade" the roof in terms of insulation anyway and thus the felt very likely? Link to comment Share on other sites More sharing options...
GaryA Posted September 7, 2023 Share Posted September 7, 2023 Did Building control allow you to keep the 1F felt underlay or did they insist on a breathable felt? Link to comment Share on other sites More sharing options...
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