r values

[zepesh]

Hi Everyone
This is the first of probably many future questions on a project I have going on here in France.
I am taking down an old French farmhouse over here that is pretty knackered and create a new house on a larger footprint.
Our major demands it must be clad in the traditional sandstone random stonework to blend in.
My question is which has the greater insulatory properties:
A conventional cavity wall with 50mm of polystyrene or 300mm aireated concrete block with no cavity.
The clading will be 200mm thick.
Cheers
Frank

 

[mointainwalker]

A conventional cavity wall made of .........what ?

If you already have specific types of blocks in mind, then the data sheet which is normally kicking around somewhere in your builder's merchant will give insulation values which you could post here if you need to.

The cladding only adds a very small amount of insulation.

Be interested to hear how you get on. The French don't seem to use cavity walls, at least not in my area, and so when wanted wall-ties complete blankness followed by curiousity about this strange "practice"

O.K. Have just looked up aerated block and found a R value of 1.7 for a Celcon-type block of 300 mm, but don't know if this is the same as a Siporex, but the data-sheet will tell you.

50 mm of exp poly insulates better with an R value of 2, even before taking the cavity and other blocks into account.

Don't know which region you're in, but if much heating at all required, I would probably put at least 100 mm poly in the wall, but don't know what block-laying probs this might cause

 

[mointainwalker]

Apologies, getting my wires crossed here.

50 mm of exp PS only gives an R of 1.25 and the air-gap adds 0.20 so that's 1.45.

If you then used 100 mm clinker-blocks in your two walls, that would add R 0.36

Total R 1.8 vs 1.7 for the Celcon 300 mm block ( but you need to check if your block is the same )

Pretty much the same,with small advantage to the cavity route, so down to a time/cost analysis by you, although the cavity with carefully-installed poly sheets is going to resistant to damp whereas that's something else you presumably need to build into the aerated block scenario

 

[zepesh]

Am in the tarn et garonne and here they use cavity walls all the time,even our existing 1800s house uses walnut shells and maze husks.Hot summer with short but cold winter.
As I will probably doing most of the block work time is not to much of an issue and as the airated blocks come in at 82 euros per square metre I think the cavity wall is the way to go.
Shall price it all out just to make sure.
Cheers

 

[drnail]

yeah personaly id go for the 9 inch block work then clad it with celotex then lay ya sandstone block will give you tremendous warmth