Cold Extension - Insulation Issues?

[EinTopaz]

Update on this one, I took some tiles off to have a better look at the eaves detail. Was difficult to photograph so i've done a short video instead.

Summary of problems & questions.

• Gaps between roof kingspan and wall plate,
  • Can the gaps here be simply foamed to improve insulation / stop wind draughts going into the plasterboard?

 

• Large gap between wall kingspan and inside block wall.
  • It really shouldn't be like this right?
  • again can the fix be foam the gap between block and kingspan, then put the wool back over?#

 

• Wall king span had quite a bit of movement / play in it.
  • Do i need to fix this if i foam the gaps between the kingspan and block?

 

 

Here's the video with all the detail.

 

 

 

 

 

[MikeGrahamT21]

Firstly the easy bit, the Kingspan to wall plate junction, yes this can be foamed and obviously ensure the gap above remains clear.

 

and here in lays the problem why PIR cavity insulation gets such a bad rap!! Poor installation. You are correct that will be doing very little work currently, in practice when it was installed and built up, plastic retaining rings should have been installed to keep it held tight against inner leaf. Clearly doing this now would be a major major job.

 

what size cavity is it and what thickness were the boards? How clear is the cavity on the outer leaf side? I’m thinking your probably going to need some sort of wedge, but it’ll be difficult for it to not just dig into the PIR

[ETC]

Roof and wall insulation should overlap.

The wall insulation should be tight against the inner leaf.

I suspect the timber batten was an attempt to close the cavity at the eaves for fire.

Don’t use foam.

Get the works done properly.

[EinTopaz]

16 minutes ago, MikeGrahamT21 said:

 

and here in lays the problem why PIR cavity insulation gets such a bad rap!! Poor installation. You are correct that will be doing very little work currently, in practice when it was installed and built up, plastic retaining rings should have been installed to keep it held tight against inner leaf. Clearly doing this now would be a major major job.

 

 

 

struggling to see them on the WIP photos but the bricklayer did have these little pin things that were holding the insulation in place. Edit: I think i've found an imagine with them on. (attached below)

Also interesting to see the insulation is snug against the inner block wall on the images. So maybe it's just come away at the top where he's run out of using the plastric retaining rings?

 

[EinTopaz]

18 minutes ago, MikeGrahamT21 said:

what size cavity is it and what thickness were the boards? How clear is the cavity on the outer leaf side? I’m thinking your probably going to need some sort of wedge, but it’ll be difficult for it to not just dig into the PIR

 

It's 100mm insulation, I didn't measure the full cavity thickness annoyingly and it's dark now, but i'd hazard a guess at 150mm. The issue is even when I was pushing the kingspan toward the block with a fair bit of force I couldn't get it flush. Maybe down to 10mm gap.

 

So thinking i'm gonna have to seal it with something, even with a wedge between brick and insulation. If that makes sense. 

[EinTopaz]

19 minutes ago, ETC said:

Roof and wall insulation should overlap.

The wall insulation should be tight against the inner leaf.

I suspect the timber batten was an attempt to close the cavity at the eaves for fire.

Don’t use foam.

Get the works done properly.

 

I need the least invasive / best solution here, I can't remove the outer brickwork and can't remove the roof rafters etc. Original builder not an option now either and not contactable. (even if I would have them back)

[IGP]

Wow, that’s er not good in the politest sense… 

 

I wonder if you could drill through the wall and through the PIR, and using a really long toggle to allow you pull the PIR to the inner leaf, working from the bottom up. 
 

Otherwise, given that the PIR is loose inside the cavity, I don’t suppose there is an option of removing it somehow, then once done, fill with blown EPS beads?

[gravelld]

2 hours ago, EinTopaz said:

On which image are you seeing the 5.5 degrees? It'll likely be inside yes. 

 

walltoroof.thumb.jpg.9e8fff6f087d3bdfcc7f4a8e526e48af.jpg - looks like there's a projector or something in the photo...

[gravelld]

Christ that video is so disappointing. This is exactly what people are talking about when we question the knowledge and skills gap amongst trades.

[MikeGrahamT21]

1 hour ago, IGP said:

Wow, that’s er not good in the politest sense… 

 

I wonder if you could drill through the wall and through the PIR, and using a really long toggle to allow you pull the PIR to the inner leaf, working from the bottom up. 
 

Otherwise, given that the PIR is loose inside the cavity, I don’t suppose there is an option of removing it somehow, then once done, fill with blown EPS beads?

https://www.buildingmaterials.co.uk/info-hub/insulation/can-cavity-wall-insulation-be-removed
 

Looks like polyurethane can be removed, according to that anyway, may be worth speaking to the experts, call a removal company and see what they say?

[ETC]

It looks like it might just be the top board that’s loose. Pause the video. Pull it back in place as best you can and fill any voids with mineral wool/rockwool.

Extend the PIR between the rafters to the wall plate.

Seal the top of the cavity wall with a bagged cavity barrier.

Don’t block the eaves ventilation.

[Onoff]

Unfortunately the whole construction method has loads of non airtight "gaps", PIR against the timber, even timbers ostensibly butted up against each other. It all adds up.

 

[EinTopaz]

16 hours ago, MikeGrahamT21 said:

Looks like polyurethane can be removed, according to that anyway, may be worth speaking to the experts, call a removal company and see what they say?

I think that's a decent shout. I'd be surprised if they can get this stuff out though with it being the interlocking type. They'd have to remove loads of bricks. But you're right - I can absolutely see what they say. 

[EinTopaz]

16 hours ago, gravelld said:

Christ that video is so disappointing. This is exactly what people are talking about when we question the knowledge and skills gap amongst trades.

Tbh Im not surprised. Glad I found the source of some of the issues. I knew there'd be something, there had to be. That room is SO cold. Makes sense if the wall insulation layer is essentially negated.  Hopefully can sort it.

[EinTopaz]

14 hours ago, Onoff said:

Unfortunately the whole construction method has loads of non airtight "gaps", PIR against the timber, even timbers ostensibly butted up against each other. It all adds up.

 

 

Yes, I never took a photo of it before I removed the wool. but they'd basically sat the wool atop of the wallplate. and had it sort of dangling down into the cavity between the insulation and block. But by no means air tight. 

[EinTopaz]

15 hours ago, ETC said:

It looks like it might just be the top board that’s loose. Pause the video. Pull it back in place as best you can and fill any voids with mineral wool/rockwool.

Extend the PIR between the rafters to the wall plate.

Seal the top of the cavity wall with a bagged cavity barrier.

Don’t block the eaves ventilation.

 

Thanks, I need to remove a load more tiles when I've got a dry couple days and take a proper look at what's going on. I'm hoping it is just the top board that's loose, but then I would've suspected to see a huge temperature difference from the internals in that case, and I didn't really. 

 

The issue I found was when I tried pushing that top board closer to the block, it didnt want to go.... but i'm thinking that may be because they've stuffed wool down the gaps between the wall kingspan and blockwork, obviously not in this rafter channel as i removed it, but in the ones adjacent. I'm thinking i'll need to remove all that wool, push the kingspan up close to the block, wedge it there with something, tape/foam/seal it. 

Then deal with the roof insulation and running that to the wall plate after i've sorted the wall kingspan gap.

 

Out of interest what is a bagged cavity barrier? as in a cavity closer? 

 

 

[ETC]

The builder should have closed the cavity at the top with a half-hour fire-resisting cavity barrier.

You have plenty of options but I suspect the least time consuming will be a bagged fire barrier. If you put one in you need to close the cavity before you extend the insulation between the rafters down to the eaves.

 

You can use a strip of 12mm thick calcium silicate board - Supalux or other equal board. This might be the easiest in terms of space  but it could tern out to be time consuming.

[ETC]

@EinTopaz

[EinTopaz]

18 hours ago, ETC said:

@EinTopaz

 

@ETCThat's really helpful thanks for sending that detailed cross section, it makes sense. I was hoping the PIR overlap bit could be achieved with rockwool atop of sealing all the gaps beneath it with foam etc.

 

For the cavity barrier, Arc do a 150mm deep version which is what i'd need to close the cavity but it's also 120mm tall. The PIR wall insulation already sits higher than the outer leaf brick so i'm not sure how i could make that work. Unless i'm misunderstanding.

Also the PIR overlap you detailed there, I assume i'd be fine doing that in 2 pieces? Like so

[EinTopaz]

Another update on this one, 

 

So I took a look at another portion of the roof to compare. Had the same problem with gaps in the insulation and wall plate etc. But also noticed something interesting when I dug a little deeper.

 

Beneath the wobbly pieces of wall PIR insulation, they looked to be sat atop of a black material that i'm wondering is a cavity closer?  Video below.
 

 

 

 

Looking back through the WIP videos of the building stages. Im guessing the blue circled stuff is what im seeing in that video? I assume that's a cavity closer?

 

 

 

 

If it is , then based on these 2 images and difference in height between kingpan and inside leaf,  it looks as if  for whatever reason they've closed the wall cavity, then added another half a course of block, then added the wall plate, then sat another piece of PIR insulation atop the cavity closer. Is that weird? and is it an issue or fine? 

 

 

Edited February 26 by EinTopaz

[MikeGrahamT21]

Black above the openings under the insulation will be DPM, its your cavity tray

[EinTopaz]

On 26/02/2025 at 12:48, MikeGrahamT21 said:

Black above the openings under the insulation will be DPM, its your cavity tray

 

Is it fine that they've sat insulation atop of that then? Maybe that's the why the pieces are wobbly and not up tight against the inner leaf. 

[MikeGrahamT21]

3 hours ago, EinTopaz said:

 

Is it fine that they've sat insulation atop of that then? Maybe that's the why the pieces are wobbly and not up tight against the inner leaf. 

yeah that’s how it should be above the openings. The dpm is to catch any potential future leaks and channel them to the outside.

 

it’s possible you have a cavity tray all way round, depending on ground conditions, but it’s not necessarily in all situations 

[ETC]

That’s the stepped DPC above your window. A cavity closer will be either a rigid board like Supalux or a flexible friction fitted sleeved mineral wool closer like the one I posted earlier.

 

I don’t see a cavity closer and the insulation is “wobbly” because it’s just set on top of the stepped DPC and fitted without any wall ties or retaining clips and that’s probably why it’s not sitting flush with the inner leaf.

[EinTopaz]

thanks both, Well then i'm hoping the PIR below the stepped dpc thing IS tighter to the inner leaf blockwork but i guess that's gonna be real tough to confirm.

 

I've got a few roofer quotes to just de-tile/de-baton/de-felt the entire roof for me. I think im just gonna go ahead with that. and foam / tape all the gaps I find in the roof insulation

Question though - If the roof rafters are 200mm thick and the roof kingspan between them is 100mm fitted towards the lower side. Will it be fine for me to add another 50mm insulation ontop so long as it doesn't block the cavity for air flow between rafters and felt? Just thinking while the roof is bare, can't hurt for me to throw some more insulation in there.

Edited February 28 by EinTopaz