External Insulation Around External Chimney

Duffers11

We will be applying 150mm platinum external insulation to our new build shortly but just have a query in aspect to one part. Have 2 external chimney breasts and I want these to be finished in stone. With the insulation wrapped around the breast I'm wondering will this withstand the weight of the stone?? Thanks

kieranhr

Easiest thing to do is build an actual leaf of stone (200 mm preferably) off a blockwork base, and tie this back to the chimney through the external insulation for lateral stability only. Otherwise you're messing around with steel bracket details. The external insulation is not load-bearing, so you can't clad directly on to it.

Duffers11

I was thinking if we applied a smaller level of insulation and use marmox board which is load bearing. Do you think that would suffice, say if it was 10-20mm thinck. Its just to continue the insulation and no cold bridge but maybe the thin insulation would be better to hold the stone??? If not, in what way would you apply it as suggested, use ties? sry if I seem stupid ha!

sas

If you are insulating around your chimney the chimney itself is still a BIG cold bridge because the chimney structure will conduct heat vertically.

Unless of course you've managed to design this out in which case you can ignore me.

The suggestion you've already been given is the way to go i.e. Stone built off it's own foundation and tied into the chimney through the insulation.

kieranhr

Get the external insulation contractor on board early with the detailing of same. I would continue the weatherproof render around the back of the stone, because the stone leaf itself won't be watertight. The ties will be a cold-bridge through the insulation, but the heat loss will be negligible.