Installing rigid insulation in cavity

[jesteh]

We had to knock down inner blockwork on our extension down to floor level and rebuild it. Problem is, outer brick wall is already built so we can't easily pin rigid kingspan insulation down again with clips.

What are our options now - I heard that its possible to push insulation against the inner skin of the outer wall - is that acceptable solution? Is there a way of squeezing the insulation into a part built wall or similar. Any thoughts?

 

[RedHerring2]

How about replacing with a full-fill cavity insulation:

http://www.just-insulation.com/pdfs/rockwool/Rockwool_Cavity.pdf

But notice you'll need cavity trays installed.

 

[^woody^]

Full-fill quilt can be used, but you'll have to confirm if it equals the u-value of the kingspan and air cavity

Otherwise, it is possible to build the inner skin and fit the kingspan to it as you go. Your brickies just have to be careful with the mortar snots

Don't put the kingspan on the outer wall

 

[jesteh]

Well building inspector said at first, stick the insulation boards on the outside then changed his mind and now insists on rockwool (he won't accept anything else).
He's happy to carry on using 75mm cavity but reading the rockwool spec, we'd have to use 90mm rockwool in 105mm cavity to comply to building regs for extension.
I am a bit annoyed as the inspector won't now let us use Kingspan boards we already bought under any circumstance and then incorrectly advised that we can continue with 75mm cavity and 65mm rockwool insulation would be sufficient.

 

[^woody^]

The BCO can't stop you re-using the kingspan boards. He is overstepping his remit

 

[jesteh]

I haven't got much choice about it. I even spoke to Kingspan (and Xtratherm) and they told me what BCO says goes. I've asked him to explain and his answer was you can use what you want but if you want it to pass you'll use full fill. He feels that anything else will not be a good enough job as it won't be perfectly flush against the wall.

 

[^woody^]

He feels that anything else will not be a good enough job as it won't be perfectly flush against the wall.

Then he has not got a clue.

A competent brickie can easily do this, and it will be as flush as if it was built like it in the first place

The BCO can't guarantee that the insulation will be flush even if the inner skin was built first, so his opinion is rubbish

I would tell him to do one, and to offer to let him look at it once built - which is what he should be doing and not telling you how to build. His job is to check not manage

 

[jesteh]

Woody, he's already made us drop the brickwork once and now blockwork as he wasn't happy with the work. The current builder says if he asks for to be dropped again, he doesn't want me coming to him to redo iit for free.
Admittedly, there were problems with how the original builder has done the work, but there is no compromise with this BCO - any problems and he wants everything re-done. I haven't really got much recourse - everyone tells me I would be mad to complain about BCO.

 

[^woody^]

The wall must have been really poor for the BCO to want it taken down. . It's very rare for this to happen

Or, you may have a little Hitler inspecting the work and he relies on you submitting to his power trip

BCO's can insist on poor work being corrected, but can not tell you how to build.

If you rebuilt the wall and put the insualtion on and it was badly done, then fair enough the BCO has cause for complaint, but until you do this he has no authority to instruct you how to build.

But having said that, if your builder was bad enough not to even be able to build an internal block wall, then putting insulation on properly may be outside his abilities ... so yes go with the BCO

 

[jesteh]

They put the damp proof course a block level too low and there was some old mortar in the cavity (which was all still at least a brick height above finished floor level) which is why he asked for it to be knocked down - otherwise it was structurally sound . There were other possible ways around which we suggested but he wanted it knocked down so thats what we had to do. At the time, he said you can reuse the insulation, just pin it on the external wall rather than internal (I have since found out that this is not recommended by Kingspan).
When it was knocked down, he looked at it and said its only going to be a good job if we use full fill and he no longer thinks its viable to pin insulation against the outer wall.

One question - can you push and clip the board insulation against a partially built block and then build up the remaining blockwork against the board. That way mortar snots would be contained in the blockwork by the board ? My brickie is saying that wouldn't be structurally sound - blockwork must be built with nothing against the wall and then board must clipped after the mortar is put in. Is he right?

 

[^woody^]

Two courses are laid and any snots on the back are removed.

Then the boards are put in and the ties bent down and clipped. As the ties are already built into the outer wall then they don't move and the clip stays tight.

Additional ties can be bent and then fixed over the insulation and laid on the bed to hold the insulation back (or bent in a u shape and placed over the block and insulation so that one end is in the cavity and one end on the inside face.

Then the bed of the next and subsequent course is laid keeping the mortar off the top of the insulation, and then the next row of insulation is put in.

It takes care, and the brickie needs to avoid throwing mortar all over the place, but its certainly possible

 

[jesteh]

Thanks - that makes perfect sense.
At the moment I got a good brickie who is not keen on doing it and building inspector who refuses to pass it. Any thoughts on how to overcome those two?

 

[RedHerring2]

Two courses are laid and any snots on the back are removed.

Then the boards are put in and the ties bent down and clipped.

Sorry to disagree a bit Woody. According to Kingspan, the inner skin is built, 450mm at a time, then the insulation placed, then the outer skin built up to level with the insulation, then that process is repeated.

http://www.insulation.kingspan.com/uk/pdf/k8.pdf

 

[^woody^]

Sorry to disagree a bit Woody. According to Kingspan, the inner skin is built, 450mm at a time, then the insulation placed, then the outer skin built up to level with the insulation, then that process is repeated.

http://www.insulation.kingspan.com/uk/pdf/k8.pdf[/QUOTE]

Follow the thread, the outer wall is already up.

I was commenting on a way to rebuild the internal wall and re-use the kingspan

 

[^woody^]

. Any thoughts on how to overcome those two?

You have to decide if you are confident that the brickie can do this, and if so then you have to be assertive with the BCO and tell him that you are doing it this way and he is welcome to inspect the work in progress.