dpm under a hearth?

9 Sep 2008
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United Kingdom
I am putting in a new hearth over an old concrete slab floor.
The rest of the floor will be as follows (top down);
screed (with UFH) 75mm
insulation 60mm
DPM (1200 gauge visqueen)
Old Concrete Slab

When it comes to the hearth I know that I need to have a constructional hearth at least 125mm thick that extends out 300mm in front of the stove.

But what I dont understand is what to do to dampproof under the hearth.

Do you need to leave an airgap over any dpm?

Or is there a fireproof DPM?


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A constructional hearth is for a timber floor. You need a superimposed hearth, and there is no need to put a DPM under it.
thanks for the reply.

is there no need for a dpm even if there is no dpm under the concrete slab and there will a dpm under the rest of the floor?


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Sorry, I misread your post. I thought that the screed ran into the fireplace and the superimposed hearth was to sit on top. I see now that you are putting in a separate concrete hearth, and running the screed up to it, and then putting a superimposed hearth on top. You could use a DPM under the concrete hearth. Concrete floors have a DPM undernearth which also extends under the fireplace. It won't catch fire as there is no oxygen fot it because it is trapped in between the concrete. If you are really concerned I suppose lead is a fireproof DPM.

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