Hi,

 

I have been trying to research this topic and came across this post with nearly the same sort of setup 

 

I have my PIR continued up the wall as suggested, and I'm wondering what can be used in the overhang between the joists, on the outside of the building. The commenter at the bottom of the thread says `rockwool` but my location means I can't get this easily or quickly delivered. Are there other products that would be suitable? I don't expect any water in here and I am only trying to reduce the risk of condensation. I would imagine `glass wool` wouldn't as it could absorb moisture. Would polyster insulation rolls like this from screwfix be suitable (reading online about polyster seems to suggest it is a bit like mineral wool in the sense it is moisture resistant). 

 

Thanks,

Peter

I may be wrong but I am sure I have wrung water out of Rockwool like out of a sponge, so I am not sure it is water-resistant. Is it not that the rigid or semi-rigid 'batts' may have a water-repellent coating?

Cork board, perhaps? Or perhaps not is low cost is a criterion.

EPS type insulation? Cheapest rigid board type insulation?

Just building on the above, we had a warm  flat roof, and large over hangs in a few areas, inclusive of a 30cm overhang all round. Builder used PIR for the 150mm up to wall insulation meeting it, then used Jablite (??) which was a white polystyrene type with lots of black dots throughout for the external elements.

 

This sort of thing....

 

https://insulationgo.co.uk/75mm-eps70-expanded-polystyrene-insulation-board-jablite-of-4/

Edited November 4, 20241 yr by Andehh

I'm just noticing the link to the forum post I was talking about did not go through ok. Here it is here. And attached is the picture I refer to.

 

Thanks for the replies everyone. I continued my research a bit more before I saw these and found a stockist of DriTherm Cavity Slab 32 insulation slab which use case seems similar. I would prefer a flexible product over a rigid board to be able to stuff it into the spaces I have created, but that's just a preference. I will look into the boards as well. My overhang is about 112mm and I already put the fascias on because I was in a race against the Scottish weather putting the roof on, so I just have access from below before I put the soffits on.

 

Edited November 5, 20241 yr by plockhart

Looks fine. 

 

Mineral wool and then stick on the soffits.