Suspended floor insulation - loose polystyrene

[dan offcamber]

I know its not diy but our builder who is rebuilding are kitchen ha

used spare polystyrene sheet to insulate our floor. It is a suspende floor with an air brick on the outside. I think he has loosely piled u the spare polystyrene sheet under the floor joists.

I was expecting him to batten down kingspan between the joists and tha is what he has quoted for.

Is what he has done exceptable? Surely if the outside air is jus blowing through the loose polystyrene sheet it is not providin insulation to the floor? Is it to regs?

Any comments welcome

-- dan offcamber

[mail]

Dear Dan As described by you, all that he will have done is insulate the ground against the effects of cold air of the sub-floor ventilation. a) I would use PU with foil not polystyrene b) the proposal is fundamentally flawed as by definition each joist will be a "cold" bridge

If you wish to compromise on the design you could do worse than as follows

1) lay down polythene sheeting on the oversite and cover with, say, sand to reduce moisture rising from the oversite to the house. If this is concrete (as BRegs now require - no problem) 2) take up three or so joists such as to enable 1" thick or if room 2" or greater, 8x4 or (easier) 8x2 sheets of PU to be put under the floor joists but above the air bricks. Attach the PU sheets to the underside of the joist with any ingenious means you can - for example, if room nailing upwards with large headed plasterboard nails, right angle brackets on the sides of the joists to the top surface of the PU and glue and screw on into the PU - Plastic 2" washers under PU connected to stainless wire running up thru pu and fixed to joists etc etc 3) as each PU sheet is put in next to the other one it should be sealed at the lower end with say silicone to complete the vapour check and also to any wall plates abutting 4) once the whole underside is thus covered - and the edges will be difficult - you can use a foam gun and 4" pu to complete the voids in the joists giving you 5" or more of good insulation and no cold bridges

A cheap and cheerful way would be to nail netting under the joists with a staple gun and simply fill with rock wool or the like

chris

[neverwas]

Having thought about (but done nothing yet) to insulate under a Victorian suspended floor, may I check that this is OK if the floorboards are covered with underlay & fitted carpet? Celotex etc all seem to recommend methods which leave more than vanishingly small ventilation for the joists. But I can see that they also need to (i) cover their backs and (ii) provide quick solutions for the trade.