Insulating a suspended timber floor

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We have 1960s detached house which is very cold and draughty in the winter.

One of the main culprits is the suspended wooden ground floor, and I would really like to address the issue before this winter.

There is a crawl space under the floor, and 4 trap doors (under the stairs, kitchen, lounge and dining room) allowing entry; the space is just over 2ft high.

I assume the 2 most obvious techniques to insulate are either fit insulation roll between the joists held with wire/netting, or fit Celotex or similar between the joists?

I also intend to the seal the gaps between the skirting and floor, and insulate water pipes whilst I'm down there too.

Is there a big difference between the two, in terms of efficiency?

Would I be right assuming the insulation board route would be the more difficult and expensive option?
 
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Whilst I'm not normally one to frustrate the questioner by saying "search the forums", in this case there have been several threads over the years, some quite recent, that should give you plenty of information, and opinions. Search for "suspended floor insulation".

In my opinion: rigid board insulation (which I have used for this) is dearer but more convenient if you have the floorboards up. You can get a good seal against draughts by using expanding foam to fix the edges of the board to the joists. Rockwool type insulation suspended in netting (which I haven't used) is less expensive, and may be easier to install from within a crawl space if you're not taking the floorboards up. I don't think there will be a noticeable difference between them, as long as you succeed in sealing all gaps against draughts. Make sure that any under-floor ventilation by means of air bricks is maintained.

Regards
Richard
 
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I would go one step further Dicky and suggest that there have been at least ten similar threads! :p
And now this one. Maybe they should all be fused together in the form of a mega-sticky.

Cheers
Richard

PS - don't call me Dicky and I won't comment on your leotard :mrgreen:
 
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Wonder if anyone can help - I'm a heating engineer renovating my own house looking for an alternative way to support cellotex under the floor (and I want to put underfloor heating in the suspended floor downstairs). The floor joists are 75/80mm and there is no crawl space under the floor. If I fix roofing battens (19 x 38mm) to the side of the joists to hold the cellotex (even with the battens 50 percent below the bottom of the joists) I wont have enough room for the cellotex, pipe and screed. Does anyone know of a way of supporting cellotex from underneath with enough strength to support 30mm of screed on top? Thanks for your ideas.
 
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Wonder if anyone can help - I'm a heating engineer renovating my own house looking for an alternative way to support cellotex under the floor (and I want to put underfloor heating in the suspended floor downstairs). The floor joists are 75/80mm and there is no crawl space under the floor. If I fix roofing battens (19 x 38mm) to the side of the joists to hold the cellotex (even with the battens 50 percent below the bottom of the joists) I wont have enough room for the cellotex, pipe and screed. Does anyone know of a way of supporting cellotex from underneath with enough strength to support 30mm of screed on top? Thanks for your ideas.

Have you got enough room beneath the joists, to wield a hammer, or a driver, to fix battens crosswise underneath the joists, at intervals?

Or fix screws vertically into the bottom of the joists, and run a lattice of wire between them?

Fixing the Celotex to the sides of the joists with expanding foam will give them quite a lot of strength, but I think I'd want to take a belt and braces approach to take the weight of the screed.

Disclaimer - I've insulated under floors with Celotex, but never with screed on top, so I've contented myself with screw fixing before foaming.

Do you actually need a screed, for heating under a timber floor?

Cheers
Richard
 
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Whilst I'm not normally one to frustrate the questioner by saying "search the forums", in this case there have been several threads over the years, some quite recent, that should give you plenty of information, and opinions. Search for "suspended floor insulation".

Sorry, you're right; I should've searched first. :oops:
 
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Whilst I'm not normally one to frustrate the questioner by saying "search the forums", in this case there have been several threads over the years, some quite recent, that should give you plenty of information, and opinions. Search for "suspended floor insulation".

Sorry, you're right; I should've searched first. :oops:

It wasn't meant as a telling off :mrgreen:

Do you know how you're going to go about this?

Cheers
Richard
 
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It wasn't meant as a telling off :mrgreen:

Do you know how you're going to go about this?

Cheers
Richard

My current plan is take natural wool insulation down there, and staple it in between the joists, and also and insulate the pipework while I'm down there. Seal any gaps with expanding foam. The original airbricks I hope will ensure air flow and no condensation...
 
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I would be careful with wool insulation for ground floor joists.

In that use, I have heard of instances of it going mouldy.

You do get a little more moisture under there than the rest of the building, mineral wool won't be at risk of this.

Probably depends on the specific conditions.
 
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My current plan is take natural wool insulation down there, and staple it in between the joists, and also and insulate the pipework while I'm down there. Seal any gaps with expanding foam. The original airbricks I hope will ensure air flow and no condensation...

Expanding foam goes rigid and is effective for fixing and sealing rigid material like Celotex board. I don't see if working well with a flexible, fibrous material like wool.

Cheers
Richard
 
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Hi.

I did this with wool insulation and netting, pulling up the floor boards as some of the joists were not securely installed and I needed some additional wiring in for AV stuff, along with moving a couple of radiators.

So far, it's worked really well and save for the idiot installing the bamboo flooring on top (that'll be me then) it's gone well ;)
 

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