Fullfill insulation in a 75mm cavity to reach 0.28?

[^woody^]

I'm not sure where all this is going. But ..

If you have to remove the insulation then that would seem like you have to take down the inner skin

In which case you can rebuild it and reuse the same insulation

I can't see why it would be needed to demolish the wall and then rebuild with other insulation, but if so you could then potentially need to line the inner face with insulation too

Or you can do a sap calc.

But for anyone else reading, rigid board cavity insulation is one of the crapest things to use for DIY extension building. Stick with quilt

 

[tony1851]

..

rigid board cavity insulation is one of the crapest things to use for DIY extension building. Stick with quilt

Totally agree,but I think he is trying to keep the wall as it is (albeit with a lower U-value than 028) and to compensate elsewhere, rather than bother with a SAP.

 

[theoldun]

R equals Resistance.

Outside R= 0.040
100 brick R= 0.134
25mm low emissive cavity R= 0.665
40mm CW4000 celotex R=1.818
100 Celcon Standard R= 0.667
15mm Plaster dabs cavity R= 0.170
12.5mm Plasterboard R= 0.080
Inside R= 0.130
Total resistance = 3.704m2K/W = U Value of 0.28W/m2K
Corrections for cold bridging not included in above

The above is a brief copy of a calculation done by Celotex If you PM us your address we will put a copy in the post that also includes corrections. This will be acceptable to any Building Control.
Your construction meets with 0.28Wm2/K, so BI can not pull you on that, but where we think he is going to pull you is on standard of workmanship and damage to foil face of celotex, which will drastically reduce your R value of 0.665 to the low emissive cavity and you will not possibly achieve 0.28Wm2/K If he does pull you on this, then there are a couple ways of rectifying.

 

[^woody^]

I don't think the issue is the calculation or the celotex.

It seems that the OP thinks the BCO wont be happy with all the mortar snots and the reduced clear cavity and so will want the insulation taking out for that reason alone

 

[cox377]

Just checked out that doc and seen page 38. Thanks for the details.

How do I work out the area weighted calculation, I can't seem to find it on google.

Thanks in advance

James

 

[tony1851]

How do I work out the area weighted calculation,

Fairly easy to do, but difficult to explain in these circumstances.
Best thing to do at the moment would be to see what the BI comes up with. If he's happy with the cleanliness of the cavity, see what he says about the insulation. It won't be that much below 0.28, if at all (see the old geezer's calculations) and if he is not happy, just offer to put some extra insulation in the roof. If he's in a good mood, he might just say OK, without asking for figures. If not, you'd have to get back here and see what can be done.

 

[cox377]

Thank you guys,

I'll let you know how I get on tomorrow.

When I spoke to BCO this morning he basically asked how I would show him the bottom was clear. I'm under the impression that as long as it's below the 215mm DPC line it's okay?

Regarding regid boards, tbh your not wrong, they're not easy to work with. I made some serious amateur mistakes.

Thanks

James

 

[cox377]

Hello guys,

The news was totally unexpected. He had a look at what I had done and said it was okay as long as I used a silica render on one of the walls internally as a belt and braces.

Thanks for all your advice guys, I know I came across melodramatic but I was planning for the worst rather than worrying because of the unknown.

Thanks again

J