Basements – insulate or not?

[Peter Smithdale]

I am working on improving (damp-proofing and insulating) a large (175m2) Victorian basement.

Current use is 8 admin staff with the usual electronic equipment. Proposed use is meeting / courses for up to 50 people.

Currently it is inadequately ventilated, damp and thermally stable – it needs no additional heating or cooling.

We will install low-energy lighting, MV with heat recovery, and a bit of heating.

Should we insulate it? Or will we, by decoupling the mass of the walls and floor, and the earth beyond (probably free-draining gravel) cause a cooling load?

[Peter Smithdale]

Further to my own question,

My BRE U Value calculator tells me that the uninsulated basement floor will have a U value of 0.32 already, the walls 0.7 or thereabouts.

My M&E tells me he thinks the heat loss from the basement will be 'minimal' and we need to insulate only to avoid condensation, as well as being very careful that the ventilation reaches into all areas.

I am concerned about cold spots high up on the basement walls (with potentially frosty ground just beyond) and so think the walls should be insulated a bit.

The basement has been used and heated for 10 years and the ground outside and below it has likely warmed up to more that the usual 10 degrees. My client is monitoring temperatures down there.

I think the best approach might be to insulate minimally if at all and monitor it. If it guzzles energy at least we will have learnt something.

[David Olivier]

Countries where basements are or were normal (Germany Canada USA etc) tend to insulate at least the wall (in energy-efficient buildings they insulate the floor). Ideally on the outside of the wall, but do provide protection from vermin eating it (seriously, this does happen).

In calculating a floor U-value of 0.3, I wonder what soil thermal conductivity was assumed (dry sand or gravel, wet clay, other). Did it take account of rainwater draining down and carrying away heat from the floor edge?

In most other buildings, a wall U-value of 0.7 would be considered poor – it hasn't met the UK Building Regs since about 1982. I suppose of course you might heat such a room electrically; i.e., by having inefficient electrical appliances and office equipment, but how sensible is this in the long run?

D.

[Peter Smithdale]

Many thanks for the replies. I have heard advice – from the Rocky Mountain Institute originally apparently – that insulating the walls and the first 2m of the floor is the optimum. But I have not seen the original source material.

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