Best way to insulate a floor

  al's left peg 11:31 18 Sep 2010

Hi guys,

been thinking of doing this for a while to help save money on wasting heat through the floor of my kitchen.
The kitchen is a flat roof extension which has fibre glass type insulation in the roof, no insulation in the walls and a timber sprung floor, joists with weyroc chipboard flooring. I obviously don't want to rip the kitchen units out but am thinking of lifting the floor to insulate betweeen the joists.
My question is what do you think is the best insulation to use for this job?

Thanks in advance,

  Bingalau 11:45 18 Sep 2010

Something like polystyrene beads maybe? Easy to push in to corners and crannies.

  bri-an 12:06 18 Sep 2010

Rolls of loft insulation, thicker the better. held by plastic netting fixed below the joists.
Bit awkward fitting, but will do the job at low cost.

  Woolwell 12:10 18 Sep 2010

Heat rises and you want to be careful about blocking ventilation below the floor. You may already have a "warm-roof" with the right amount of insulation. Lining the walls or cavity wall insulation may be more cost effective.

  bri-an 12:41 18 Sep 2010

Ventilation below floor is to allow joists to 'breathe', but preventing this cool circulating air coming up through the floorboards is an important insulation feature.
This is what I assume Al is wanting to stop.

  Woolwell 12:47 18 Sep 2010

I assume that there is a floor covering stopping most of the air coming through.

  bri-an 13:20 18 Sep 2010

I think I may have not been clear.
The area below the joists will be cold, just like the outside of the walls , and should have insulation. All new properties have this, often using Celotex or similar.

I think you may be talking about draughts from underfloor, which can be stopped,as you rightly say, by carpeting.
But I assumed Al wanted insulation, not draught-proofing.
Sorry for any confusion.

  Woolwell 13:27 18 Sep 2010

I think we are in general agreement.

One of things that may be needed with increased insulation is better ventilation/heating in the kitchen otherwise there could be increased condensation especially on cold exterior walls. What we do not know is how old this extension is and how it was constructed.

  bri-an 13:33 18 Sep 2010

Absolutely, which also explains the regulations about extraction units being obligatory in 'condensation' areas for all new-builds.

  al's left peg 13:50 18 Sep 2010

Hi bri-an and woolwell, It was constructed in the late 80's it is a really cold room. I have heard that it is possible to put Celotex between the joists and that is what I am thinking needs doing, or that sort of thing.
It has a door leading to the living room, a door to the garage and a door to the back garden. The floor is covered with laminate, not the best for a warm feeling but the missus does not want carpet in there. I believe there is enough ventilation in the area to keep condensation down.
Thanks to alll the advice upto now.

  bri-an 14:04 18 Sep 2010

Celotex is easily 'cuttable' but still needs supporting between the joists. It's more expensive, but easier to handle than fibrous material.
Bit more of a challenge with Celotex to get all areas covered as opposed stuffing in fibreglass (particularly at the edges where joists meet walls) - but it's purely a matter of personal choice.
We normally do this pre-floor laying, so it will be messier for you, but best of luck with it.

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