Cold Extension - Insulation Issues?

[ETC]

Yes. 50mm air gap is normal.

[Iceverge]

Skimmed this thead. 

 

Airtightness is the main culprit although the insulation details aren't anything to write home about either.

 

Thermal camera, drill and squirt in some illbruck FM330 any cold spots. 

 

Isolate the electrics, take off the socket face plates and seal the back of the boxes with acoustic sealant too. 

 

Keep at it every night for a week it'll make a big difference. 

 

 

[MikeGrahamT21]

On 28/02/2025 at 22:51, EinTopaz said:

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.

Yeah that’s doable, as long as you maintain a 25mm air gap up to the breather membrane your good

[EinTopaz]

2 hours ago, MikeGrahamT21 said:

Yeah that’s doable, as long as you maintain a 25mm air gap up to the breather membrane your good

Cool, probably a silly question but does it have to be PIR type up there or could I use rockwool slabs / rockwool rolls? as it already has 150mm kingspan, this is just topping it up. Though wasnt sure if wool is the wrong material to use up there if it gets damp etc? 

 

[EinTopaz]

14 hours ago, Iceverge said:

Skimmed this thead. 

 

Airtightness is the main culprit although the insulation details aren't anything to write home about either.

 

Thermal camera, drill and squirt in some illbruck FM330 any cold spots. 

 

Isolate the electrics, take off the socket face plates and seal the back of the boxes with acoustic sealant too. 

 

Keep at it every night for a week it'll make a big difference. 

 

 

thanks for taking the time to comment.

We've had a tightness test done and it wasn't as bad as I thought, main culprits were under skirts (now sealed) gaps between wall and window frames in the revels (now sealed)... sockets (now sealed)... and weirdly the door architrave leading back to the rest of the property (now sealed).

I think i'll have a decent level of access for the cold spots from the exterior, that's what im hoping. Plan today is to get up there in the eaves and properly insulate / seal everything I have access to. Trying to minimize interior works where possible.

 

 

 

[EinTopaz]

i'll be up in the eaves insulating today so did a quick video this morning with the thermal cam to form the before portion of a before / after. Figured I may as well share it should anyone else be struggling with the same issues and comes across this thread maybe it'll give some good insight, there are obvious very cold spots in the walls / roof still that i'll be continuing to address from the exterior.

 

I'll do another one of those after i've done all my insulating / sealing today and (hopefully, dear lord) it makes a difference.

 

Thermal imaging with air gaps rectified, insulation not yet rectified

 

 

 

[Iceverge]

2 hours ago, MikeGrahamT21 said:

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.

 

 

2 major problems, 

 

1. AIRTIGHTNESS. I cannot emphasise this enough. It's massively more important than insulation.
2. Continuity of Insulation, obvious to see. 
3. Thermal bridges. 

Ok you have lots of options. The cheapest one is just to get a few boxes of IL330 and the thermal camera and drill holes and give a good squirt anywhere it's cold. Evenntually you'll have a reasonable job of the airtightness. 

 

 

However as you're prepared to take the roof off and have clearly got the bit between you teeth here's my suggestion for an absolutely pucker repair.  

 

ROOF

1. Strip the roof. leave the PIR in place.
2. Add 45x45mm battens at 90 deg to the rafters on top 
3. Sheath the roof with 11mm OSB.
4. Add Noggins between the rafters to close the gap in line with the external leaf of the wall. 
5. Inject Open cell foam like ICYNENE into the 145mm space above the PIR allow it to fill the gap in the eaves outside the wall plate and above the wall too. 
6. Breather membrane on top.
7. Batten along the line of the rafters for ventilation. 
8. Batten across the rafters for tiles. 

WALL

 

Inject closed cell foam into the cavity from outside. it will completely expand pushing the PIR boards against the inner leaf and prevent any air movement in the cavity. 

 

 

 

Edited March 2 by Iceverge

[Iceverge]

Here's what you have

 

 

 

Here's what the air is doing. 

 

 

[Iceverge]

 

 

There we go. 

 

That should prevent any drafts. @Gone West used Icynene for airtightness on his passivhaus project. 

 

There's vastly improved bridging qualities through the rafters and at the wall roof junction too. 

[Gone West]

2 hours ago, Iceverge said:

@Gone West used Icynene for airtightness on his passivhaus project. 

Yes, we didn't use any tapes or membranes, just the exterior racking OSB3 and internal plasterboard.

[EinTopaz]

3 hours ago, Iceverge said:

 

 

2 major problems, 

 

1. AIRTIGHTNESS. I cannot emphasise this enough. It's massively more important than insulation.
2. Continuity of Insulation, obvious to see. 
3. Thermal bridges. 

Ok you have lots of options. The cheapest one is just to get a few boxes of IL330 and the thermal camera and drill holes and give a good squirt anywhere it's cold. Evenntually you'll have a reasonable job of the airtightness. 

 

 

However as you're prepared to take the roof off and have clearly got the bit between you teeth here's my suggestion for an absolutely pucker repair.  

 

ROOF

1. Strip the roof. leave the PIR in place.
2. Add 45x45mm battens at 90 deg to the rafters on top 
3. Sheath the roof with 11mm OSB.
4. Add Noggins between the rafters to close the gap in line with the external leaf of the wall. 
5. Inject Open cell foam like ICYNENE into the 145mm space above the PIR allow it to fill the gap in the eaves outside the wall plate and above the wall too. 
6. Breather membrane on top.
7. Batten along the line of the rafters for ventilation. 
8. Batten across the rafters for tiles. 

WALL

 

Inject closed cell foam into the cavity from outside. it will completely expand pushing the PIR boards against the inner leaf and prevent any air movement in the cavity. 

 

 

 

 

thanks for the detailed steps and the cross section in the other reply too. 

Sorry if a silly question - but if you're packing all that tight into the roof cavity, wont that stop any air travelling through it? Or is that why you've suggested open cell foam? will that still allow air to pass through?

Same question for the walls. In eliminating the 50mm airgap between brick outer leaf and PIR, wont that become an issue with damp bridging? i thought thats what the airgap was there to prevent.

Edited March 2 by EinTopaz

[EinTopaz]

3 hours ago, Iceverge said:

Here's what you have

 

 

 

Here's what the air is doing. 

 

 

 

 

Yes, so again thanks for this. 

Ours (as im sure you've seen on the video) looks more like this - as the roof PIR does end pretty short of the wall plate.

 

 

 

What i've done today is remove the wool that was sat atop the wall plate (they'd actually done a terrible job where they'd entirely blocked the cavity between pir and felt here so needed to come out anyway as it was wet!) then where the Red X's are, i've sort of packed the gaps with wool, foam sealed, cut the excess foam off, electric tape over the top, then reinstated the wool. I'm yet to see if it's made a difference, but in principal its following your guidance of the air flow getting into places it shouldn't being the biggest causer of issues. So i'm hoping it makes a difference, albeit less of a pucker fix than your suggestion.

 

 

 

 

 

 

I plan to do the same methodology to the entire roof, as a bare minimum, if what i've done today helps. As simply taking the front 2 rows of tiles off all the way round didn't give me access to all the bits I needed. So Yeah i do wanna do a full pass with a roofer.

 

 

 

Edited March 2 by EinTopaz

[EinTopaz]

Found a particularly horrendously poorly section on the front section.

4 hours ago, EinTopaz said:

i'll be up in the eaves insulating today so did a quick video this morning with the thermal cam to form the before portion of a before / after. Figured I may as well share it should anyone else be struggling with the same issues and comes across this thread maybe it'll give some good insight, there are obvious very cold spots in the walls / roof still that i'll be continuing to address from the exterior.

 

I'll do another one of those after i've done all my insulating / sealing today and (hopefully, dear lord) it makes a difference.

 

Thermal imaging with air gaps rectified, insulation not yet rectified

 

 

 

 

 

Found a really bad section on the front right corner earlier today, its now rectified (to the best i could given the access i have) but look how bad this is! 

 

 

 

[Onoff]

5 hours ago, Iceverge said:

The cheapest one is just to get a few boxes of IL330 and the thermal camera and drill holes and give a good squirt anywhere it's cold. Evenntually you'll have a reasonable job of the airtightness. 

 

Isn't there a risk of encroaching on the 25, 50mm or whatever gap under the membrane doing that and thus comprising the air flow? 

 

(Don't get me wrong I love FM330).

[Iceverge]

1 hour ago, EinTopaz said:

Sorry if a silly question - but if you're packing all that tight into the roof cavity, wont that stop any air travelling through it? Or is that why you've suggested open cell foam? will that still allow air to pass through?

The 50mm ventilation in this case is above the membrane. Hence the extra batten running up the line of the rafters.  Completely fine. We did it on our house. 

 

Open cell is more vapour permeable. It won't trap moisture in the roof timbers and cheaper, preferred for the roof. 

 

Closed cell is quite dear and has much lower vapour permeability. How's it may be subjective to driving rain seeping through the bricks so being waterproof is preferred in this application. 2 neighbours have done this exactly buildup on their walls on purple and have had good results. 

 

 

 

 

 

 

 

 

 

[Iceverge]

Airtightness and vapour permeability are two different things. 

 

 

 

Airtightness is to do with literal holes and gaps that wind can blow through. This is how almost all airborne moisture (originating inside the house) gets into a structure and causes damage. This is the BIG one in preventing interstitial condensation. Like hundreds or thousands of times more than Vapour permeating through the fabric of a structure. 

 

 

Vapour permeability is essentially microscopic holes in the material itself. Something like paper or wood fiber insulation will be relatively vapour open (plenty of microscopic holes) Something like a sheet of polythene or the foil facing on PIR is very vapour closed (very few microscopic holes) .

 

These microscopic holes are much too small to make any difference to airtightness but they do allow some drying of the material inside. 

 

The most tangible example of this is to put some damp leaves in a paper bag and seal it and similarly in a plastic bag. Put them in a warm cupboard. 

 

Both bags will hold air but the paper one will gradually allow drying Vs the plastic one which will end up with a rotten sticky mess. 

 

This matters for all buildings regardless of material but especially where organic products are used (eg timber).

 

TLDR.

 

1. Pucker job on Airtightness 

2. Don't sandwich stuff between two layers of impermeable material. 

[Iceverge]

1 hour ago, EinTopaz said:

What i've done today is remove the wool that was sat atop the wall plate (they'd actually done a terrible job where they'd entirely blocked the cavity between pir and felt here so needed to come out anyway as it was wet!)

 

The mineral wool is almost certainly wet because of airborne moisture condensing as it makes its way outside and condensate. 

 

Wool is NOT airtight!  If you are sealing this I would recommend you use some Airtight tape or sealant or foam. 

[Iceverge]

Before

 

 

 

After

 

[Iceverge]

Before

 

 

AFTER

 

[EinTopaz]

5 hours ago, Iceverge said:

Wool is NOT airtight!  If you are sealing this I would recommend you use some Airtight tape or sealant or foam. 

I did wool down the gaps, foamed over the top, cut back, then taped over. Probably overkill. But gonna see the difference over night tonight. 

[MikeGrahamT21]

That is a spectactularly bad job on the builders part, that corner is a proper shocker, basically zilch insulation!

[EinTopaz]

11 hours ago, Iceverge said:

Before

 

 

 

After

 

 

Thanks for these @Iceverge the roof one may be a bridge too far for me and my skills.  But the wall one i'm interested in so long as it wont cause damp.  

 

How do you limit the insulation from rising above the clay brick height when doing this? Will the installer just know what to do? Or will i need to block something off in the wall cavity to prevent it rising too high, if that makes sense? 

[Iceverge]

1 hour ago, MikeGrahamT21 said:

That is a spectactularly bad job on the builders part, that corner is a proper shocker, basically zilch insulation!

 

I have never ever seen PIR boards fitted properly between timbers or in a cavity wall. 

 

I actually don't think it can be done. 

 

This of course was a poor effort but sadly I've seen worse. 

[EinTopaz]

1 hour ago, MikeGrahamT21 said:

That is a spectactularly bad job on the builders part, that corner is a proper shocker, basically zilch insulation!

 

I know, frustrating. Even more concerningly that corner explains why this bit on the thermal image was darkened.

 

 

 

So imagine what im gonna find here as it's way colder!..

 

 

through frustratingly i think this bit is gonna require the valley to be removed to see it properly... as it's past where the roof turns on the 90degree angle. So can't access it from this side annoyingly.  I estimate it to be around here.

 

 

[Iceverge]

3 minutes ago, EinTopaz said:

But the wall one i'm interested in so long as it wont cause damp.  

 

Closed cell foam is watertight so ingress isn't really an issue. 

 

4 minutes ago, EinTopaz said:

How do you limit the insulation from rising above the clay brick height when doing this?

 

Not 100% sure for foam. We closed our cavity with a 500mm strip of held under 2 x wall plates but that was for EPS beads.