Unavoidable thermal bridge with 100mm polished concrete floor?

23 Nov 2021
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United Kingdom
Am I right in thinking that thermal bridging where a 100mm polished concrete floor meets a door/glazed area is inevitable? We have cavity walls - we were going to lower the inner block and extend the insulation through to the outer block. I understand that normally perimeter insulation would be used, and then the final floor covering would cover that. However, in this case, because the final floor covering is 100mm, there's no room for perimeter insulation (unless it was to remain visible)?

Secondly, if this is the case, how significant will it be? We will have UFH so will definitely lost a bit of heat here. But will it be a major cost-issue? With thermal bridging, as long as the heat loss isn't insane, I am mainly concerned about condensation/mould. But I figure if the UFH is always on low in winter, this will keep the area warm.

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You may get some condensation on your door frame. Is the door going to be on a concrete cill?

My sliding door has a kind of sacrificial Plastic strip on the inside for condensation, it’s embedded in an oak threshold.

When it’s really cold, I give it a wipe in the morning If it’s wet (not everyday).

There should be perimeter insulation (For bridging) and a layer of compressible foam 10mm For expansion of the screed when warm.

Cost issue, unlikely, with a thick screed it will hold heat a long time. I’ve got around 65mm liquid screed and it will stay warm most of the day before firing up again to top it up.

why not put perimeter insulation in but make it, say, 70mm tall, that way you can have a 30mm strip of polished concrete on top, it might minimise the bridging.

will be interested in hearing others comments.
@Mr Chibs thanks - the idea of 70mm (or thereabouts) perimeter insulation is a good idea as a bit of a compromise - I would need to check with the concrete people whether they think there's any risk of cracking in the area that will then just be 30mm (as they say min 75mm normally).

I am not 100% sure about the doors/cill - I have just messaged our door providers to understand better. Would a cill normally be provided by the door/glazing manufacturers, or would we need to organise that ourselves?
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Yes, cracking may well be an issue, bugger it’s near the door:cautious:

The door should come with a cill, upvc/wood/metal.

Sometimes these are sat on a concrete cill/brick depending on what you have.

Presume you will be having a flush floor to the doors cill?

What about a 5/10mm gap from floor to door with coloured silicon Infil?

Keep us updated, keen to know.


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