Is this normal?

[MrGreen]

We’ve been really happy with the work our contractor has undertaken so far, and great bunch of lads etc but we took a look at the insulation they’ve started installing in the roof today and…I dunno… is this bad? The intention is that there will be 50mm PIR backed plasterboard going over the top of this so all these badly fitting parts won’t be visible but I’m worried it will affect the thermal performance. Any thoughts?

[Nickfromwales]

Every gap needs to be foam-filled.

 

Clearly there's too much product been installed for these guys to go removing this and replacing with new stuff, cut better, but TBH if they do the foam work meticulously then you'll be fine. It is sloppy work, so time for a cup of tea and a chat with them to say this won't fly.

 

With the second layer, this can be saved, but ask them to take more time and cut this lot in much better from this point forwards. Tell them you absolutely must be given the opportunity to check this has been done properly before they even think about covering it over with the next layer  

 

https://www.dortechdirect.co.uk/catalog/product/view/id/3337.html?gad_source=1&gad_campaignid=17178602520&gbraid=0AAAAADt-Kn3-BTy4AWmJ2n3r3P3VUbGyt&gclid=CjwKCAjw7fzDBhA7EiwAOqJkh4MpaBgc0DV6KYyQXIXuvbklpz7uRhLHx1CZLxqHq1Z_zTRfAfuj_hoCpuQQAvD_BwE

 

That is closed cell, high quality foam that wont bridge damp/moisture. They cannot use regular foam now, as any that accidentally reached the roof felt/membrane will cause you huge issues (regular builders merchants foam will NOT suffice here).

[MrGreen]

10 minutes ago, Nickfromwales said:

Every gap needs to be foam-filled.

 

Clearly there's too much product been installed for these guys to go removing this and replacing with new stuff, cut better, but TBH if they do the foam work meticulously then you'll be fine. It is sloppy work, so time for a cup of tea and a chat with them to say this won't fly.

 

With the second layer, this can be saved, but ask them to take more time and cut this lot in much better from this point forwards. Tell them you absolutely must be given the opportunity to check this has been done properly before they even think about covering it over with the next layer  

 

https://www.dortechdirect.co.uk/catalog/product/view/id/3337.html?gad_source=1&gad_campaignid=17178602520&gbraid=0AAAAADt-Kn3-BTy4AWmJ2n3r3P3VUbGyt&gclid=CjwKCAjw7fzDBhA7EiwAOqJkh4MpaBgc0DV6KYyQXIXuvbklpz7uRhLHx1CZLxqHq1Z_zTRfAfuj_hoCpuQQAvD_BwE

 

That is closed cell, high quality foam that wont bridge damp/moisture. They cannot use regular foam now, as any that accidentally reached the roof felt/membrane will cause you huge issues (regular builders merchants foam will NOT suffice here).

Thanks for that Nick, I feel a bit reassured. I’ll be making sure that the foam infill is perfect and done with the correct product. 👍

[Nickfromwales]

Just now, MrGreen said:

Thanks for that Nick, I feel a bit reassured. I’ll be making sure that the foam infill is perfect and done with the correct product. 👍

Just ask (tell) them to make sure not to squirt loads of foam in and that then gets to the felt, you just need the gaps filled slowly and with the minimal amount of foam getting behind the boards. They'll need to leave it to expand and cure, and then for it to be cut back flush, before the next layer of boards go on.

[MrGreen]

Will do. Cheers Nick.

[Redbeard]

Can you clarify the depth of the PIR already fitted? To get a reliable 0.16W/m2K there should be at least 150mm total. I really do not like plasterboard/insulation laminates as you do not get a stab at taping the joints. When I did this sort of work I would (a) have tight joints unlike those shown (b) have taped all the joints on the (100mm) between-rafter PIR, then fitted 25mm PIR under the rafters, and taped) then fitted 25 x 50 laths across the rafters, with a further 25mm between, then finally a VCL ('ordinary' or 'intelligent', taped at all joints and perimeters) before the plasterboard.

[MrGreen]

12 minutes ago, Redbeard said:

Can you clarify the depth of the PIR already fitted? To get a reliable 0.16W/m2K there should be at least 150mm total. I really do not like plasterboard/insulation laminates as you do not get a stab at taping the joints. When I did this sort of work I would (a) have tight joints unlike those shown (b) have taped all the joints on the (100mm) between-rafter PIR, then fitted 25mm PIR under the rafters, and taped) then fitted 25 x 50 laths across the rafters, with a further 25mm between, then finally a VCL ('ordinary' or 'intelligent', taped at all joints and perimeters) before the plasterboard.

So, this is an old chapel conversion that we are doing. Slate roof over Sarking boards.we left a 50mm air gap then what you are seeing is 100mm of PIR. Once that’s all (correctly🙏) fitted, there will be a layer of 50mm PIR-backed plasterboard going on top.

[SteamyTea]

PU/PIR sheets will shrink over time, the only way to stop the edges becoming thermal bypasses is to use a very low foaming adhesive, properly applied.

This sill not stop the sheets becoming slightly thinner of the years, but as the thinning is a percentage of length, thickness thinning is not so much of a problem.

While tapes can cover any gaps, that is all they do, and again, they have to be properly applied.

 

I love expanding foams, I made a living out of making the tooling for them, but you have to know the curing characteristics and limitations of them.  Curing can happen for months after moulding and natural temperature variation will cause 'off gassing' that further changes the ratio of the material to void matrix (bubble size effectively).

[Roger440]

You can of course buy gapo tape. Then shrinkage isnt any issue.

 

But it is bonkers expensive.

[Nickfromwales]

13 minutes ago, Roger440 said:

You can of course buy gapo tape. Then shrinkage isnt any issue.

 

But it is bonkers expensive.

And you have to remove all the installed PIR to fit it.

 

Chillax peeps, a good afternoon with some 330 and a bit of GAF and this can be brought back into 2025 without having to re-mortgage .

 

I would say that the above is good advice; buy the 2 layers of PIR, and then tape the joints, then install standard plasterboard with long screws.

[torre]

Have they bolted timbers to the existing rafters? Is that to a SE's design? 

 

From an insulation perspective, it looks like those new timbers may be wider than the original joists in which case the gaps between insulation and the original joists behind will be much bigger

 

 

[MrGreen]

10 minutes ago, torre said:

Have they bolted timbers to the existing rafters? Is that to a SE's design? 

 

From an insulation perspective, it looks like those new timbers may be wider than the original joists in which case the gaps between insulation and the original joists behind will be much bigger

 

 

Te gap behind is necessary for airflow so not too worried about that. 👍