Floor insulation-old wooden

[ssray]

We have a 1903`s semi, and as we are on a hill we have a void/cellar of approx 10-12ft under the ground wooden floors.

Is it worth insulating under the floorboards? its quite draughty so the other day I filled some gaps from below with expanding foam(mainly brickwork), I dont want to encorage rot, so would it be ok to use a thin sheet of celotex cut up and pushed in between the joists from under neath?

Ta
Ray

[Busamav]

you need to place the Celotex tight to the underside of the boards , cut tight for an interference fit ,

then leave the ventilation to the floor void below , this is important.

[ssray]

Thanks, kinda what i thought
Ray

[ndg]

I did this on our house 2 months ago. I used regular fibreglass stuffed up and then supported with a breathable membrane (weed membrane in our case) to support it after it inevitably sags in the future. I went with fibre to maintain the overall breatability of the structure, we don't have any damp, and I don't want it appearing!

Edited to add:
This is well worth doing, it made an instantaneous difference to the feel of the (uncarpeted) house, went form drafty old house to quiet, still house.

N.

Edited by ndg on Friday 4th December 18:48

[V12Les]

Worth a mention: Dont cut the strips to tight to the joists, you could end up with a squeeking floor. Leave a slight gap, you can always fill with foam if you wish.

[GuinnessMK]

Insulating under the floor boards is well worth it. We have a Victorian Terrace and had all the floor boards / joists up in the ground floor due to a damp problem. As we put the floor back down, we insulated all the central heating pipework that was running in the void, insulated between the new joists, and then put the floor back down.

Before doing that the central heating was on 6 most of the winter, now it's down at 1! Make sure your airbricks are clear at the front and rear of the property to keep the void well ventilated. We had to extend ours down below the level of the insulation.

[anonymous-user]

In an old house like that how about using some sort of cellulose or sheeps wool insulation. Both are very good insulators and are breathable.

[Vee]

My extension has cellotex between the floor boards (normal joinsts on brick piers) and also in the roof.
Its approx 100sqm and only 1 of the 4 large rads is used.
Brilliant for insulating imo.

[ssray]

Thanks for the replys, NDG- I had`nt thought of using glassfiber, I think thet would work out quite a lot cheaper than celotex type stuff.
Cheers
Ray

[eps]

ssray said:

Thanks for the replys, NDG- I had`nt thought of using glassfiber, I think thet would work out quite a lot cheaper than celotex type stuff.
Cheers
Ray

Indeed, but remember not all glass wool is the same... Some will be almost useless. You can get Knauf Crown 32 (aka Ultra/Ultimate?) which will do almost as good a job as Celotex, but you'll be able to put more in as it won't need the ventilation gap below..

[ndg]

As for different types of glass, well I used regular knauf loft insulation at 100mm thick (some of the short joists aren't very deep) as it was on offer. Can't really comment on longevity yet obviously, but it's well supported so shouldn't just fall apart. The weed membrane was installed taught with lots of staples into the underside of the joists. You could use roofing membrane if you want something a little tougher and more breeze resistant.

N.

[eps]

Indeed, but Knauf do at least 3 different products in the same range, of the same depths.. All have different ratings..

See here : http://www.knaufinsulation.co.uk/products/glass_mi...

The lower the value the better it is.

[ssray]

mall update; the local recycling place sells off sheets of used warehouse etc insulation for £2 a piece,as b+q sell kingspan for £40 a sheet I`m going there.

whole ground floor should be around £12.

Ray

[mprmax]

I have an old georgian house, there is a basement under the ground floor where the floor joists for the ground floor are visible. I don't want board over the joists as I would loose to much heiht in the basement. However the basement is very cold and is chilling the ground floor.There are numerous gas and water and electric cables that weave though the floor joits.
I am contemplating fitting some Celotex insulation between the joists. and was wondering how I should fit it. Will I need to leave a gap between the floor and the celotex (to leave space for pipes etc). What type of celotex should i use (do i need certain fire protection properties). Are there any other things I need to consider?

Many thanks in advance

[ssray]

Have a look here http://www.pistonheads.com/gassing/topic.asp?h=0&a...
This was the update, well worth dong and even better it only cost me £12 for 15 boards I had 4 left and gave them away.
Where are you based?
Ray