Cold Extension - Insulation Issues?

[Iceverge]

23 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

 

This solution is unlightly to fix your issue as you'll still have lots of bulk air movement. Like I said AIRTIGHTNESS is the huge issue here.

 

If I was doing it myself (literally DIYing) I would consider having an external airtightness layer and full fill insulation. However I wouldn't hand this task off to anyone short of an OSD watchmaker in a cleanroom, and even then I would make sure I had mechanical ventilation internally. A dMEV like this would be fine. 

 

 

 

Open cell spray foam would be an (almost) idiot proof way to give excellent airtightness. You could omit the layer of 45x45 timbers building up the roof and settle for a U value of 0.17W/m2K.  This is probably a worthy compromise as an airtight build with any even any hint of insulation ( say a U value < 1W/m2K) will be able to be warmed to a satisfactory level. 

 

In your case you could have passivhaus U-values but the drafts will make it unheatable as you've found out. 

 

However I would keep the OSB sheathing. Spray foam involves a lot of trimming if done in an open cavity. Also I'm coming to the conclusion every roof should be sheathed for rodent protection, noise and durability in worsening weather. ( I wish I'd done ours) . 

 

 

[lookseehear]

Just wanted to send a message to say you seem surprisingly chipper given the absolute sh*t show in evidence here. So many people would just accept this as 'what it is', so kudos to you to get sorting it! I hope you retained a significant chunk of the ££ against the builder.

[EinTopaz]

27 minutes ago, lookseehear said:

Just wanted to send a message to say you seem surprisingly chipper given the absolute sh*t show in evidence here. So many people would just accept this as 'what it is', so kudos to you to get sorting it! I hope you retained a significant chunk of the ££ against the builder.

 

They're being investigated for tax evasion. Even if they weren't; based on the evidence I wouldn't want to deal with them again after this, even monetarily. Rather wash my hands.  Just keep telling my self the good old motto "if you want something done right... do it yourself!

[EinTopaz]

59 minutes ago, Iceverge said:

 

This solution is unlightly to fix your issue as you'll still have lots of bulk air movement. Like I said AIRTIGHTNESS is the huge issue here.

 

If I was doing it myself (literally DIYing) I would consider having an external airtightness layer and full fill insulation. However I wouldn't hand this task off to anyone short of an OSD watchmaker in a cleanroom, and even then I would make sure I had mechanical ventilation internally. A dMEV like this would be fine. 

 

 

 

Open cell spray foam would be an (almost) idiot proof way to give excellent airtightness. You could omit the layer of 45x45 timbers building up the roof and settle for a U value of 0.17W/m2K.  This is probably a worthy compromise as an airtight build with any even any hint of insulation ( say a U value < 1W/m2K) will be able to be warmed to a satisfactory level. 

 

In your case you could have passivhaus U-values but the drafts will make it unheatable as you've found out. 

 

However I would keep the OSB sheathing. Spray foam involves a lot of trimming if done in an open cavity. Also I'm coming to the conclusion every roof should be sheathed for rodent protection, noise and durability in worsening weather. ( I wish I'd done ours) . 

 

 

 

I don't disagree, it's just not something i'm familiar with and anxious about buggering it up. IF there was someone in the NW that could do this for me i'd be happy to look at costing it and proceeding. Just feels beyond my level of understanding and time availability to DIY on this one. But the U value numbers you've posted there have got me interested for sure. 

[Iceverge]

2 hours ago, EinTopaz said:

Just feels beyond my level of understanding and time availability to DIY on this one

 

By the time you've paid someone to do it properly spray foam would be just as economical. 

 

@JohnMo used it in his roof. Maybe he could review my idea and comment. 

[MikeGrahamT21]

I've learned from jobs over the years to always keep a very close eye on builders, i still think Unilin's (xtratherm) CT/PIR was a very easy to use product: 

 

[JohnMo]

On 02/03/2025 at 13:52, Iceverge said:

 

 

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. 

Pretty similar to what I did. I don't have any PIR where you do.

 

The noggin between the rafters is actually 140mm PIR closing that space. I have 256mm deep rafter and have under drawn with battens, to increase to 350mm. Over rafters I have sarking boards (45 Deg roof) and marine ply (12 Deg roof). All have breather membrane above. Full fill with Icynene open cell. Also have a vapour closed membrane below.

 

All seems pretty quiet and keeps the heat in. Did interstitial condensation calculations and no issues.

[EinTopaz]

Brief update on this one just so the thread and any other troubled onlookers are aware.

I've now gone through and inspected the eaves detail for everywhere I can for this extension. Found some horrifying things and insulated it the best I can. Those steps being:- 

 

:- Remove all poorly seated wool covering wall plates.
:- Seal all gaps between ceiling PIR and wall plate with wool / foam/ tape.

:- Reinstate PIR insulation where there was none
:- Form Wedge to force wall PIR to be uptight against block

:- Seal all gaps between Wall PIR and block with wool / foam / tape.
:- Reseat wool covering wall plate and all sealed areas.

 

I'm very pleased to report that this has made a huge difference. I have not had chance to put my thermal cam back on, but you can feel it in the room. It's actually retaining heat through the day now, heating on in the morning for a few hours and you could still feel the residual heat in there by midnight. Perhaps i'd got used to having essentially balls-all insulation in there so im hypersensitive, but very promising so far. and that's without any form of curtain / blinds etc. All the glazing (of which there's lots) is still entirely bare.

 

Not to say im going to stop there, I will be still removing all the roof to fully seal it and add more insulation. But atleast now my horrifying suspicion that I may need to add interior insulation in an already finished room... has been quelled. I'd REALLY hoped I wouldn't have to do that and it looks now that i wont have to, so im very glad for that atleast.

 

Id rather spend the time and money on further improving the roof, glazing and adding exterior wall insulation to the walls if I need to. 

 

 

Anyhow, some more images of fixes for future ref for anyone. 

 

 

 

 

Edited Tuesday at 13:33 by EinTopaz

[Nickfromwales]

It's staggering just how shite some trades' workmanship and standards are...

 

They just think because they've sweated for the day that it's a good days graft.

 

Good on you for sticking to this and getting the simple measures done to make a job well done, would have been so much easier if they had just given a feck..

[EinTopaz]

2 hours ago, Nickfromwales said:

It's staggering just how shite some trades' workmanship and standards are...

 

They just think because they've sweated for the day that it's a good days graft.

 

Good on you for sticking to this and getting the simple measures done to make a job well done, would have been so much easier if they had just given a feck..

 

What has double-annoyed me about this one was, they were one of the more expensive quotes we had to do the job and we went with them because of how confidence building they were. I.e they continually said things like "we are more expensive but the attention to detail and overall quality will be reflected in the price".... Being a very quality-driven type person myself that really resonated with me. But in reality I could've likely gone with the other quotes, saved £20k and invested that into these types of snags! 

That said, we can sit here and moan about it and it still wouldn't fix the problem. So rather just get it right and let bygones be bygones. I only care about the comfort level of my family. Not so much about pounds and pennies. 

[Nickfromwales]

2 hours ago, EinTopaz said:

I only care about the comfort level of my family. Not so much about pounds and pennies. 

Amen reverend.

 

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