neverending project - insulation and condensation

9 Oct 2007
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United Kingdom
Hullo. Can anyone help me to work out which way to insulate under the floor in my living room. We have floorboards and a large crawl space underneath.
DIY books and colleagues have suggested blanket insulation and netting. Have started and actually stapling the insulation material to the joists seems to work ok - netting just to hold material in place right?

What depth insulation should be used - just trying 100mm - just to stop draughts to living space from air vents underneath.
However, can't find (after searching for some time) info. on whether insulation should be butted right up against the floorboards from underneath or suspended to leave a small space between the floorboards and the bottom of the joists - not hanging below joists but so still a space between floor boards and the insulation - to trap warm air - or will this cause condensation / stale air / problems.
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The insulation should ideally be as deep as the floor joists. If not as deep, then the insulation should be tight up against the underside of the floorboards - no airspace
thanks Woody - that's kinda what I thought but only after I had come back up from under the floor! Finishing off today - thanks
Easy way is to use Celotex/Kingspan rigid board insulation.

Easily cuts into strips to fit between the joists and then use foil tape to keep it in place and seal the edges.
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thanks GoingDigital - however we'll have to stick with what we have now - although the boards would maybe have been better - there is not a great deal of space for getting them into position. We've got the eco friendly roll material so at least it's green and easy on the skin to use.

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