Replacement of felt during loft conversion

[DIYmadDAD]

 

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

[nod]

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 

[Russell griffiths]

As nod said, why are you not taking the whole roof off and re new it all. 

[tonyshouse]

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 

[Onoff]

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

[joe90]

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 ).

[DIYmadDAD]

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?

[Onoff]

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?

[GaryA]

Did Building control allow you to keep the 1F felt underlay or did they insist on a breathable felt?