Building control say I must knock down wall and rebuild??

Hi,
My builder has built a brick brick cavity wall and filled the cavity with celotex CG4000 and it meets the required U value, but hasn't left the 25mm airgap between the insulation and the external course. There is 10 - 15mm. Building control say I must rebuild with the 25mm gap. My builder doesn't want to do it.... Has anyone any idea how to get around it and keep building control happy?
Thanks
Ken

 

Ken
I think that Celotex require a 25mm residual cavity even if you do acheive the required U value. I know a builder had a simlar issue near me and was forced to pull it down.
Sorry.
C

 

A decent builder should be conversant with Bulding Regs, the materials he is using & know what to expect from local LABC inspections. Yours hasn’t followed the regs or, it appears, the insulation manufacturer’s installation instructions; make it clear to him it’s his problem not yours & if that means taking part of the wall down, it's going to be at his expense. Unfortunately, it is ultimately your responsibility to comply with BR’s; I’ve no idea what form of contract you have (hopefully you do have one!) but you should always ensure it puts the onus onto him to comply with all relevant BR’s. There are so many cowboys around, I hope you haven’t paid him too much up front!

 

To obtain 0.29Wk/m2 on brick and brick as stated and assumed no internal plaster finish, you require a minimum 75mm cavity with 50mm CW 4000 partial fill and 25mm clear cavity. A 10 to 15mm clear cavity does not comply. End of story
We hate partial fill, and when we are forced to use it, we set out our cavities at 85mm.
Sounds like BCO is not approachable, but you could try him with offering to dot and dab with insulated plasteroard internal on the brickwork, unless of course brickwork is a feature wall. If brickwork is not a feature wall, can not understand why you did not use blockwork.
oldun.

 

You can start with sacking the "builder"

I am curious as to why the builder does not want to do it. Surely building correctly would be what he wants to do, and does he have the same ethos in not wanting to put foundations to the correct depth, or not wanting to put suitable timber in the roof?

What happens when his customer does not want to pay him?

 

And end of thread, you're builder is a muppet.

 

Thanks for your replies...
The building control's problem is not with the U value but with moisture ingress. I spoke to the technical department at celotex who basically said in reality the wall would be fine, but they couldn't issue a certificate for 'one offs' their certificates have to cover all eventualities and building control want a certificate.
The new cavity wall is built on a solid 225 wall, as part of a loft conversion. Building control are worried that rain could soak through the outer course of bricks, the 10 - 15mm air gap, then the 50mm of celotex and finally the internal course of bricks and spoil the internal finish. I pointed out that the new wall it's built on is solid brick that is 120 years old and does appear to have moisture ingress... they said they don't build to victorian standards. They have said if I can get the celotex out and then fill the cavity with a 'blown' insulation they would accept that. Trouble is that it would probably take longer (if at all possible) to do that than rebuild the wall.
Cheers

 

Your builder and you need to face the reality that he has F***ed up, it’s a school boy error!

 

Despite this not being constructed to the manufacturers recommendations, there is very little chance of water penetration tot he internal face.

If the BCO is worried about this, then it is possible to dry line the internal face to ensure that any water penetration is kept out - this will be exactly the same as lining a solid wall which is acceptable to building control

Alternatively, you could dispute the BCO's view and ask for a relaxation of this part of the b/regs, and appeal the BCO's request. This would need to be supported by an experts report and opinion to justify this method of construction

 

Thanks for your replies.
Ken

 

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