moldy

Cavity block with external insulation

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I've seen a few builders do block on flat combined with external insulation. What are the pros/cons of using cavity blocks with external insulation?

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If your building a cavity then why would you put the insulation on the outside??

Much easier to use the cavity in the way the vast majority of traditional builds do and stick the insulation in there.

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Cavity block is common term for hollow block where I am based. Apologies for confusion. 

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It's becoming more and more popular and in many ways is better than the likes of ICF as you're mostly using cheap and readily available materials. Cold bridge elimination is much easier than with block cavity construction. Same applies for structural elements - your structural elements will all be within the thermal envelope. I'm building with ICF as I don't want to be weather dependent... But would chose this as a second option.

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+1 on what Conor says.

I thought long and hard on this (single block and 250mm EWI) and ended up with ICF but its still a option on next build. Would tie in very nicely to a insulated raft foundation. 

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1 hour ago, moldy said:

Cavity block is common term for hollow block where I am based. Apologies for confusion. 

 

Just saw your post on the Self Build group on Facebook, I'll not repeat myself then :)

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I would think it would be a bugger to fit anything to the outside insulation, ok if your rendering but no fixing points if you are cladding. 

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Passive House Mag has a article on this,

 

https://passivehouseplus.ie/magazine/new-build/ireland-s-largest-passive-house-scheme-shows-way-to-nzeb

 

Their quote about the hollow (cavity) blocks was 

 

" The use of single leaf walls of hollow blocks – which use some 30 to 40% less concrete than a comparable solid block, and are relatively quick to build with "

 

I assume that as it was commercial development the cost was a deciding factor. Another thing that sprung to mind was the reduced weight of the walls, approx 454kg/m2 for 1m2 of block on flat vs 264kg/m2 for hollow blocks. This could bring savings by reducing the foundations needed.  

 

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