Roof repair - can I use torch-on felt nailed only, as underlay (instead of 1f)?

[udaman]

Hi

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- ... m-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

IMG_20231001_194412397.jpg (336.82 KiB) Viewed 920 times

[aeromech3]

I am imagining you are going to lay this new stuff over the old where there was a flu.
This will be like patching a bicycle inner tube and I would recommend a coat of Blackjack Bitumen type around the perimeter of the cut out and across the top of the overlap.
Only an I think: better the thicker stuff, warm day and use a heat gun to help lay it flat.
Clout nails seal by the bitumen clasping around their stems to form a seal, are the new nails also going through the existing 1F.

[udaman]

HI @aeromech3 and thanks for the reply.

No, I'll likely be removing the old felt in the area. I need to get to the sarking board beneath, cut that out, and replace with new. Can't think of a way of doing that and still being able to re-use the existing felt.

With that in mind, would you still recommend the same? Or with the new sarking board in place, could I simply roll out the torch on and nail it to the rafters, then back on with the battens (in other words, us it just like I would if it were 1f)?

Cheers

[aeromech3]

Umm!, are your sarking boards beneath the rafters as your suggesting nailing the felt to the rafters.
As you are only using the felt as a second skin to the slates your only real concern should be the overlaps and sealing the edges.

[udaman]

Umm!, are your sarking boards beneath the rafters as your suggesting nailing the felt to the rafters.

No, sarking boards on top of rafters. I planned to nail the felt through the sarking and into the rafters. As per how the battens are also fitted.

As you are only using the felt as a second skin to the slates your only real concern should be the overlaps and sealing the edges.

OK, but is it enough to give plenty of overlap in terms of distance, but still only nail the felt? If I were using 1f all I'd be doing is nailing it. So I guess my main concern is whether torch-on can be substituted for 1f but used in the same way 1f would be used.

Thanks for all your help.