Cavity block extension - best insulation?

Leprechaun77

I am currently deciding on the type of insulation for a small kitchen extension about 22m squared. The construction will be standard cavity block with a pitched roof. I have received two different opinions in relation to this and am unsure how to proceed. The two options are the standard dry-lining with 100mm xtratherm method, and the second is spray foam insulation.

While the spray foam option is deemed better from an air-tightness point of view, I am thinking that this might be overkill considering the rest of the house is nowhere near this level of insulation. I would be grateful for any thoughts on this from those with experience in this area.

Gumbo

If I was going down the dry line option, maybe the internal face of the block could be sand/cement rendered before attaching the battons that hold the insulation?

sky6

You would be better off building a Cavity Wall with 4 inch Blocks. You'd be amazing the difference that alone will make to the Room. Then you can Fill the Cavity any time you like. You'll also save 8 inches of floor space.

+ 1 for what Kceire has recommended also.

Calahonda52

Leprechaun77 wrote: »

I am currently deciding on the type of insulation for a small kitchen extension about 22m squared. The construction will be standard cavity block with a pitched roof. I have received two different opinions in relation to this and am unsure how to proceed. The two options are the standard dry-lining with 100mm xtratherm method, and the second is spray foam insulation.

While the spray foam option is deemed better from an air-tightness point of view, I am thinking that this might be overkill considering the rest of the house is nowhere near this level of insulation. I would be grateful for any thoughts on this from those with experience in this area.

What's the basis for the better A/T with the foam: do you have a spec sheet?
The reason I ask is that there are two main types of spray foam, open and closed cell, the latter is denser, more expensive, better insulation for the same thickness, better resistance to moisture penetration.
The attached link gives an idea of the comparisons.

http://walltite.basf.ie/services/material-performance.

What I have seen mostly is the quy in the suit, in the liveried van, quotes for closed cell with labeled samples, and the guy in the white van, usually NI or UK reg, sprays open cell.

There is also a moisture retention issue to be considered so the moisture needs to move through the wall from inside out, the sand cement kc suggest allows this but don't get conned into a quick coat of skim, it proms mould and is not moisture permeable

Gumbo

Calahonda52 wrote: »

What's the basis for the better A/T with the foam: do you have a spec sheet?
The reason I ask is that there are two main types of spray foam, open and closed cell, the latter is denser, more expensive, better insulation for the same thickness, better resistance to moisture penetration.
The attached link gives an idea of the comparisons.

http://walltite.basf.ie/services/material-performance.

What I have seen mostly is the quy in the suit, in the liveried van, quotes for closed cell with labeled samples, and the guy in the white van, usually NI or UK reg, sprays open cell.

There is also a moisture retention issue to be considered so the moisture needs to move through the wall from inside out, the sand cement kc suggest allows this but don't get conned into a quick coat of skim, it proms mould and is not moisture permeable

If cavity blocks are being used with insulated plasterboard on battons on a strip of dpc, would you still/also recommend the cost of sand/cement?

Calahonda52

kceire wrote: »

If cavity blocks are being used with insulated plasterboard on battons on a strip of dpc, would you still/also recommend the cost of sand/cement?

The sand cement I presume you have in mind for airtightness and if the rigid insulation is all taped up and applied in two layers with staggered joints then the alu facing should do it.


Like Bob and Mondays, I don't like cavity block...:D
They are fine for walls with no opes and corners but otherwise just too messy.

Gumbo

Calahonda52 wrote: »

Like Bob and Mondays, I don't like cavity block...:D
They are fine for walls with no opes and corners but otherwise just too messy.

So garden walls I suppose yeah