Leca underfloor insulation

RobertL

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Mar 28, 2012, 5:58:53 AM3/28/12

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Our conventional victorian house has just been extended slightly. We are using Leca (lightweight expanded clay aggregate insulation fill material) under the new concrete floor (dig down 400mm, lay 300mm of Leca granules, vapour barrier, 100mm concrete). That is the approved sequence.

Leca looks like cat litter and so it would be easy to pour it into the void under the suspended wooden floors of the rest of the house, leaving an airgap above. There would be no concrete above it. The sequence would be:

bare earth | 300mm Leca | 100mm ventilated airgap | suspended wood floor

Are there damp issues with this? The ventilation would flow above the Leca. Woul dit achieve any heat insulation.

Of course, Buildign Control wouldneed to agree to it, but I wondered if anyone had experience of doing this.

thank you

Robert

NT

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Mar 28, 2012, 6:39:14 AM3/28/12

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If ventilation is above the leca, no damp problem in the floor. There
might be with the lowest bricks. And of course no benefit.

NT

RobertL

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Mar 28, 2012, 7:08:20 AM3/28/12

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Well, the benefit depends if the heat is mostly lost into the earth below or mostly into the ventilation air. If the air movement is small then presumably it's all by conduction into the ground in which case insulation below the air gap would give a benefit.

Robert

geraldthehamster

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Mar 28, 2012, 8:25:35 AM3/28/12

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I agree, no benefit at all. You need your insulating materials
directly under the suspended floor, and the ventilated space
underneath. I can't see any way to do that with Leca, without building
a platform for it to sit on (which might then collapse) . People
generally insulate under suspended floors with Celotex or rock wool.

As an aside, many years ago I had a holiday job at a plant in Essex
that made Leca. Easily the worst job I've ever had.

Cheers
Richard

NT

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Mar 28, 2012, 5:21:30 PM3/28/12

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And that means taking the floor up. If you can do it its worth it, but
of course its hassle.

NT

RobertL

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Mar 29, 2012, 6:43:20 AM3/29/12

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I think there woudl be a good market for a retrofit insulation product that could be fed between the joists by lifting one board on each side of the room. Robert

RobertL

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Mar 29, 2012, 6:23:54 AM3/29/12

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On Wednesday, March 28, 2012 10:21:30 PM UTC+1, NT wrote:

yes, I suppose I have to do that. i had a glimmer of hope that I could lift just one board and pour in the Leca. Clearly that's only going to reduce the part of the heat loss that goes to the earth under the house rather than the bit that goes via the airflow.

Robert

NT

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Mar 29, 2012, 7:19:38 AM3/29/12

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Since the underfloor cavity is wide open to the elements, just pouring
leca would achieve not much. Sorry.

NT

geraldthehamster

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Mar 29, 2012, 8:03:57 AM3/29/12

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> I think there woudl be a good market for a retrofit insulation product that could be fed between the joists by lifting one board on each side of the room. Robert- Hide quoted text -
>
> - Show quoted text -

Some sort of helium-based expanding foam might do it ;-) Except it
would float up through any gaps in your floor, and stick to the
ceiling.

I went round the houses trying to find a way to insulate under my
suspended ground floor, without lifting it, before lifting it and
insulating with Celotex.

If you're lucky enough to have a deep enough void under the floor, you
might be able to crawl underneath and do it that way. Mine,
unfortunately, was only 9 inches (though I'm told that's enough).

Regards
Richard