Green Building Forum - Roof repair - can I use torch-on felt nailed only, as underlay (instead of 1f)? Thu, 30 Apr 2026 12:47:57 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Roof repair - can I use torch-on felt nailed only, as underlay (instead of 1f)? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303687#Comment_303687 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303687#Comment_303687 Tue, 03 Oct 2023 19:45:20 +0100 greenfinger
Apologies as this isn't really a "green" building question... But you've been a great help in my other queries, and I'm not having much luck finding an answer on this one.

I've got a repair to do to my roof. The roof has sarking boards, with 1f felt on top, battens, then slates. I'm repairing a hole in the sarking and felt from where a flue was removed. The whole area to be repaired amounts to approx. 1.2m x 1m.

I was kindly given some felt to use for the repair. I was told it was 1f but I've collected it and it's actually torch on. In fact, I was given two different rolls. One is this stuff:

https://www.jtatkinson.co.uk/iko-glass-torch-on-app-universal-underlay-16m-61020216

The other felt is thicker and I'm guessing is used for the top layer in a torch on system? Photo below of that one....

My question is whether either of these can be used instead of 1f for the repair? I'm only looking to nail it, as you would with 1f. Or do I need to make a trip to the BM and fork out for a roll of 1f?

Many thanks]]> Roof repair - can I use torch-on felt nailed only, as underlay (instead of 1f)? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303697#Comment_303697 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303697#Comment_303697 Tue, 03 Oct 2023 23:11:45 +0100 tony Roof repair - can I use torch-on felt nailed only, as underlay (instead of 1f)? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303702#Comment_303702 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303702#Comment_303702 Wed, 04 Oct 2023 00:27:53 +0100 greenfinger
It's going on top of sarking boards so sag shouldn't be an issue.

Didn't realise there was a possibility of a reaction though, that doesn't sound good! Is that something specific to using the torch on with 1f? Or can it happen with other felts too?

Thanks again]]> Roof repair - can I use torch-on felt nailed only, as underlay (instead of 1f)? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303704#Comment_303704 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17981&Focus=303704#Comment_303704 Wed, 04 Oct 2023 07:41:53 +0100 tony