Wall Insulation problem - help

[noseall]

I'm relaying what the technical team at Celotex told me.

I'm discussing from a builders' POV.

None of the full fill rebated PIR systems we have used have required fasteners. They are designed so that the inner or outer leaf can be built first.

All cavities need to be at least 10mm bigger than the product simply to make them fit.

There isn't a builder or robot on the planet that can build two leaves of masonry walls and maintain a constant 10mm gap.

 

[noseall]

Ok so they're being made, and recommended by Celotex

Yes - for partial fill, whereby the cav' boards are fitted tight to the blockwork, i.e. blocks first then bricks.

 

[robinbanks]

There is enough give in foil faced celotext that you could fit a 90mm board plus an 8mm fastener you're determined to use into a gap 94mm wide. Go push your finger into one of the boards and you'll see what I mean

If you want to get out on site with a grinder and flap wheel and shave the fasteners down a few mm I can't guarantee that the builders won't find it amusing, but if it helps you sleep at night, go for it.

Sometimes it's wise to let clients do what they think is best, when there is no overall detriment to their approach, as there is a mental benefit for them

these thick rigid boards don't want to sit against the block

Yeah, but don't forget, that those small air pockets on the inner side trap air, improving your U value and allow the foil face to reflect, improving your U value. A perfectly built block-5mm air-90mm foiled PIR-5mm air-block wall has a fractionally better U than a block-90mm foiled PIR-10mm air-block one

ideally no gap at all really

The foiling needs an air gap to deliver its tiny reflective/emissive benefit. With no gap, it ceases to be antiradiant/reflective. Don't get too fixated on this part of the science though, it's incredibly small benefit in the overall scheme of things

 

[James Davis]

There is enough give in foil faced celotext that you could fit a 90mm board plus an 8mm fastener you're determined to use into a gap 94mm wide. Go push your finger into one of the boards and you'll see what I mean

Wrong.

That would break the outer foil.

This is a partial fill system requiring 90mm board and a 10mm air gap. The further from the inner leaf the boards are, the less benefit, hence building inspectors wanting, and celotex recommending, fasteners to hold it against the inner leaf. Also maintains the outer air gap and, added benefit, a moisture gap. All of this adds up to the right way of doing it. I'm not saying it is absolutely necessary or the end of the world if not followed, just stating the facts. If mine has 8mm air gap, I won't care in the least, but builder is aiming for plan and product specifications to the best of his ability.

 

[James Davis]

Yes - for partial fill, whereby the cav' boards are fitted tight to the blockwork, i.e. blocks first then bricks.

Which is what my system is.

Dot and dab plaster board, fibolite block, celotex therma class 21, 10mm air gap, outer brick.

 

[Deluks]

It's interesting that you've titled this thread "

Wall Insulation problem - help​

And then argued against all the help you've been given by the various helpful tradesmen that have replied.

 

[James Davis]

It's interesting that you've titled this thread "

Wall Insulation problem - help​

And then argued against all the help you've been given by the various helpful tradesmen that don't

Why are you being prickly?

If you read the first two posts of the thread you would see we solved the problem for ourselves and have corrected course. All my responses since are factual and reasonable. Each to their own, take it or leave it.

 

[noseall]

Why are you being prickly?

If you read the first two posts of the thread you would see we solved the problem for ourselves and have corrected course. All my responses since are factual and reasonable. Each to their own, take it or leave it.

No. You are not listening.

 

[James Davis]

No. You are not listening.

Are you nuts or something?

You have been arguing whilst talking about a different system. Mine isn't full fill.

And I haven't said anything controversial here, just reported what celotex are saying and what is on my plans. I have acknowledged it can be different on site and may be variations.

 

[noseall]

Are you nuts or something?

You have been arguing whilst talking about a different system. Mine isn't full fill.

And I haven't said anything controversial here, just reported what celotex are saying and what is on my plans. I have acknowledged it can be different on site and may be variations.

Partial fill = 50mm air gap.

 

[James Davis]

Partial fill = 50mm air gap.

You were wrong about the 10mm air gap having thermal properties. Fact.

Wrong. You were wrong.

Thank you and have a nice day

 

[Ivor Windybottom]

Wrong.

No

Wrong.

Why are you being prickly?

Are you nuts or something?

You were wrong about the 10mm air gap having thermal properties. Fact.

Wrong. You were wrong.

Were you looking for information/advice or just wanting a keyboard war?

With your interpersonal skills you'll need one of these after your brickie does the sensible thing and walks off the job...

https://www.screwfix.com/p/marshalltown-brick-trowel-10-/47283

 

[noseall]

You were wrong about the 10mm air gap having thermal properties. Fact.

Quickly negated by snots cold bridge and discrepancies, once the masonry starts off the damp.