Extension Blockwork Issues

[robinbanks]

I understand that there will be no heat radiation to prevent if there is no cavity, but would it be worth retaining the foil for vapour barrier purposes?

The board is still a closed cell foam with foil on the other side..

Couldn't you simply use rockwool insulation?

Given that there is merely 90mm of insulatable space, if it was a choice between 0.033 lambda wool insulation and 0.022 lambda PIR, I know which I'd choose..

 

[johnny2007]

The board is still a closed cell foam with foil on the other side..


Given that there is merely 90mm of insulatable space, if it was a choice between 0.033 lambda wool insulation and 0.022 lambda PIR, I know which I'd choose..

I've built lots of extensions with rockwool insulation and never had a problem.
My own extension is built that way and it's the warmest room in the house in winter and the coolest in summer.
I've always thought this rigid insulation to be just a bit of a hype to sell something that does the same thing as something else already on the market.
And don't forget the condensation problems that we've all seen/heard of because of incorrect installation of celotex.
A lot less problems with rockwool, although some customers insist on celotex and they get what they want but at extra cost.

 

[jeds]

I've built lots of extensions with rockwool insulation and never had a problem.
My own extension is built that way and it's the warmest room in the house in winter and the coolest in summer.
I've always thought this rigid insulation to be just a bit of a hype to sell something that does the same thing as something else already on the market.
And don't forget the condensation problems that we've all seen/heard of because of incorrect installation of celotex.
A lot less problems with rockwool, although some customers insist on celotex and they get what they want but at extra cost.

Mineral wool insulation won't comply with regs at that thickness.

 

[johnny2007]

Mineral wool insulation won't comply with regs at that thickness.

Must've changed in the past 10/12 years then.

 

[jeds]

Must've changed in the past 10/12 years then.

Months, the last 10 or 12 months.

 

[jeds]

It's Celotex thermaclass 21, which is a full fill board, but allows for a 10mm residual cavity

It does allow for a 10mm cavity but it isn't essential. It can equally be fitted tight. My advice is fix the insulation in place and build the blocks as tight as you like to it, You could split the difference between the two; start with a 5, 6, 7mm overhang and then follow the bow. Once dot and dabbed you wouldn't know it.

As an aside, I hope you didn't pay Butch and Sundance the full amount before they rode off into the sunset.

 

[noseall]

Must've changed in the past 10/12 years then.

June last year. It's a right pain in the ass.

And don't forget the condensation problems that we've all seen/heard of because of incorrect installation of celotex.

What PIR cavity insulation, condensation issues have you heard about?

 

[johnny2007]

Months, the last 10 or 12 months.

I wouldn't know then, I've been retired for a lot longer than that.