[Dknotty]

We're going to be renovating our 1930s house. As part of this I would like to insulate the floor. It is a suspended timber floor, with the floor about 40cms above the ground.

We can't use spray foam insulation as the gap is too small.

What suggestions for floor insulation that won't raise the floor much or cost the earth?

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[Windows on Wash]

Is the floor covered with a vapor barrier? Where is the home?

 

[Dknotty]

Is the floor covered with a vapor barrier? Where is the home?

The house is in South West London. No vapour barrier yes, all there is at the moment is an underlay and a carpet, but as part of the renovation we will replace the carpet with an engineered floor.

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[Windows on Wash]

I am confused. Is there a dirt floor directly beneath the framing or is this floor over a basement or crawl?

 

[Dknotty]

I am confused. Is there a dirt floor directly beneath the framing or is this floor over a basement or crawl?

Yes, there is dirt floor below the joists. Quite surprising, but this is common for houses in the area!

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[Windows on Wash]

Yes. What is the moisture level and control like? Best thing might be to insulate the stem wall like we would here when we "condition" a crawlspace.

http://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

 

[Dknotty]

No idea on moisture. The surveyor's report concluded there weren't enough air bricks, but we've not had any issues with damp. The ground is very clay like and totally waterlogged in winter.

Unfortunately because the space is too small to allow safe access we can't use spray foam insulation.

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[Windows on Wash]

If you insulated the topside of the floor, you will make the joists colder and more likely to form condensation.

If the subfloor is going to be off, you can scab in some rigid foam and shoot it with spray foam if you want.