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Cavity closer across top of finished wall?


 
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Watshot

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PostPosted: Thu May 05, 2011 12:38 am Reply with quote

I've seen some diagrams which depict a closer across the top of a cavity wall at eaves height. I'm assuming as a fire break and maybe to keep out vermin.

On my single storey extension the insulation in the cavity will continue above this level to join the warm pitched roof insulation. Am I right in thinking that I will still need to use a closer, and if so, what type? The usual vertical closers with attached insulation would not be suitable as insulation will be in place already on both sides.

It looks like the sort of thing they would have used slates for years ago, if they bothered at all, but I'm sure there is a modern equivalent with less of a thermal bridge etc.

Thanks guys.
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^woody^

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PostPosted: Thu May 05, 2011 5:44 pm Reply with quote

The diagrams you saw must be from 1950's or something when cavity closing was all the rage.

Nowadays, the cavity insulation must be continuous with the roof insulation.

But if you have a partial fill wall cavity, then you would close the remaining air gap with insulation, whilst the cavity insulation continues up
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Watshot (5 May 2011)
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Watshot

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PostPosted: Thu May 05, 2011 9:18 pm Reply with quote

Not a problem with the insulation, it's all going to continue up to meet in the roof.

In fact I think it was on some of the insulation websites that I saw their diagrams which included cavity closers at the top of the wall. Bang up to date then!

If it's not a requirement then I won't bother. Thanks Woody.
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tkmax

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PostPosted: Thu May 05, 2011 9:50 pm Reply with quote

Closing cavities is still all the rage to limit air movement in the cavity and hence improve the thermal insulation of your wall. Unless it needs to be fire resistant then insulation or a mineral board laid over the cavity at the top of the outer leaf will do it. You can get compressible cavity 'socks' made for the job which are mineral wool wrapped in polythene.
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stuart45

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PostPosted: Fri May 06, 2011 2:30 pm Reply with quote

Whatshot,
What you saw in the diagram was probably 1/4 inch cement particle board or similar as a cavity closer. Blocks were also used in the past.
Nowadays the best method is considered to be using a mineral wool fire/cavity barrier as thmax stated. The main reason is that the inner skin of blockwork tends to shrink and the outer brick skin expands, sometimes causing a slight crack in the plaster around the plate. With the sock you don't get this problem.
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Watshot (6 May 2011)
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