A bit of advice please...

[23vc]

Its standard spec' I'm getting from architects since June last year i.e. 90mm insulation in a 100mm cavity.

What we’re they spec’ing before that? Are you talking rigid?

 

[Kingo206]

I'm the OP, we spec'd 100mm cavity with rockwool insulation. Until the building reg guy told us it had changed from 15 June 2022

 

[mattylad]

Is your picture the state of play now?

That's looking to me as if the inner wall has not been made?
If so can the insulation be removed from the outer wall and added to the inner clipping as it is built?

 

[Kingo206]

Is your picture the state of play now?

That's looking to me as if the inner wall has not been made?
If so can the insulation be removed from the outer wall and added to the inner clipping as it is built?

It's fully built now, but I'm thinking if we can remove the blockwork and rebuild as you suggest, I can't see it being an issue.

Just ensure the insulation is pressed to inner blockwork and clip it back.

 

[noseall]

What we’re they spec’ing before that? Are you talking rigid?

Yes. Prior it was full fill 100mm Dritherm (fibreglass).

 

[jeds]

It's fully built now, but I'm thinking if we can remove the blockwork and rebuild as you suggest, I can't see it being an issue.

Just ensure the insulation is pressed to inner blockwork and clip it back.

Not using the same insulation though. You will need full-fill insulation, which is a different product. Bear in mind also that some brands may require ungraded blocks to reach the minimum u-value with a 100mm cavity. Check what your inspector will accept and if he will want a u-value calculation?

 

[Kingo206]

Not using the same insulation though. You will need full-fill insulation, which is a different product. Bear in mind also that some brands may require ungraded blocks to reach the minimum u-value with a 100mm cavity. Check what your inspector will accept and if he will want a u-value calculation?

That's what I'm not quite getting, why can't it be rebuilt with the same insulation? The building regs inspector stated that so long as we meet the minimum 25mm air gap, it is fine.

If the following steps are taken indeed it should work right?!:

1) Remove Blockwork
2) Remove Celotex insulation 100mm
3) Remove Insulation retaining clips from wall ties
4) Install Blockwork individually
5) With every-certain number of blockwork installed - add insulation against the blockwork.
6) Apply Insulation retaining clips to wall ties
7) Repeat steps 4-6

 

[jeds]

The cavity should be 50mm, although regulations allow less over limited areas to allow for obstacles - such as passing columns etc.

If your inspector will allow 25mm then fine but I strongly advise you to get it in writing - in an email. Inspectors come and go and if another, with a different idea, comes along you will be stuffed. Again.

 

[23vc]

Yes. Prior it was full fill 100mm Dritherm (fibreglass).

Guess it’s this stuff or equivalent?

Eco-Cavity Full Fill

Insulation board suitable for full fill cavity wall applications, whilst maintaining a residual 10mm cavity helping resist moisture transfer, aids installation and accommodate mortar squeeze.

www.ecotherm.co.uk

Is that the thing to use now and carry on with 100mm cavity? I bet that takes some getting used to if you’ve been doing mainly dritherm32 etc for decades!

 

[jeds]

I spec eco cavity quite a lot because builders tell me it's one of the easier to get hold of and also one of the cheapest. Problem is, it's only 90mm and you need to be careful what blocks you use with it. Standard shield blocks don't quite meet 0.18 so you need turbo or solar blocks.

Other brands are 95mm so not a problem.

 

[Kingo206]

Thanks for all your help guys.

I just wondered, we are having a flat felt roof constructed and installed by a roofer.

We initially had drawings for a pitched roof, but the slope required is not adequate.

Would you recommend getting this redrawn?

 

[jeds]

A pitched roof could go down to 10° with the right tiles, but you must make sure any rooflights are suitable for that low pitch. Nothing wrong with a correctly built flat roof. Which would you prefer?

 

[Kingo206]

Yeah, I will certainly be going for a flat roof. Our neighbour has a pitched roof, but when a building reg initially inspected our foundation he stated that "That pitch roof is not good, unsure how it passed" and we were advised to go flat.

I just wonder whether I now have to update drawings for building regulations before proceeding, or just leave it up to the roofer to get on with his work...

 

[jeds]

Flat roofs should be correctly designed and built. Given the track record of your builder, I'd be inclined not to let him just get on with it. Not saying you need highly technical drawings, but a spec and simple sketch, agreed with BC, at least - or crayons if that will make it easier for him to follow.

 

[Kingo206]

Thought I should provide an update on this for anyone in the future, we eventually went with taking down the blockwork and trying to tie back to blockwork.

Building regs stipulated that we call them out once we have reached just below shoulder height on the rebuild. On inspection the inspector said it was fine, and we are okay to proceed. See image below.

Thank goodness.