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

[Black Timber]

Hi

Apologies as this isn't really a "period property" building question (although 1f felt is quite old school now!)... 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:

IKO Glass Torch On App Universal Underlay 16m - 61020216

IKO Glass Torch On App Universal Underlay is a great product, made of a glass fibre base and coated with APP modified bitumen. This product has a flame dispersible polyethylene on the bottom surface for application, whilst the top is finished with sand. When using underlay you heat the...

www.jtatkinson.co.uk

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

 

[Zebra]

You can apparently use torch on felt just nailed. I haven't done it and I don't know how you'd overlap around the edges of the patch if it needs to be watertight. But are you going to remove a section of roof tiles to do it? Will you repair the boards as well, or just patch in with the felt?

 

[Black Timber]

Many thanks for the response.

Yes, I'll be removing slates and then cutting out the damaged sarking and replacing with new sarking. It's right up near the ridge, so the felt will be able to start at the ridge and overlap wherever I cut the old stuff lower down. If that makes sense?

Great news if torch on can just be nailed. Which of the two would you use if it were you? The thinner underlay as per the link, or the one I took a photo of, which is much thicker and I presume a top felt?

Thanks again

 

[Zebra]

I mean, anything would be fine, as it'll be covered by the slates and not subject to direct weathering. I'm not sure of the merits of the different types. I've used the torch on stuff, and it's thicker than normal (cheap) nail-on felt, so I think would last longer whether torched on or nailed.

 

[88v8]

I've used nailed torch-on as a finish coat on a shed, still good after ten years.