Underfloor boards

Any reason why you can't put fibreglass between the joists then plasterboard the ceiling? This would not reduce the height by as much.

It does have fibreglass stuffed between the joists and held there by fricti-- It was also noted that fibre quilt insulation had been fixed between the floor joists we assume to try to insulate the floor. This form of insulation is inappropriate for use in basements as damp conditions cause condensation to form between the quilt and the floor timbers. We therefore recommend that all the quilt insulation be fully removed. If the floor is to be insulated then Kingspan insulation board should be used.

So what warm air is in contact with which cold surface? Doesn't seem logical somehow.

Hmmm...could well be true with open gaps between the joists stuffed with fibreglass. However plasterboard (possibly the type with a built in vapour barrier) should seperate the joists and the fibreglass from the damp environment in the basement. Worth checking, because Kingspan is not cheap.

In article , David WE Roberts writes

You don't want a vapour barrier on the cold side of the insulation (the basement will generally be cooler than the living space). If there is one at all it should be on the warm side but it is debatable whether it is practical to include one in a retrofit installation.

IMV the surveyor is misguided, insulation in older, established buildings, is tricky but if there are no signs of condensation within existing insulation (following deep inspection) then I would be inclined to leave it as is (except for the improved insulation offered by the same thickness of Celotex et al).

A recent thread on underfloor insulation re-covered all the old arguments, I suggest the o/p have a search on google groups to see if you can track it down, celotex +floor +foam should cover it.