# minimal thickness floor insulation?



## craigs (17 Oct 2020)

Hi Chaps,

So moving on from the ceiling which ended up being 100mm rockwool sound insulation slab and 11mm OSB3, its time to tackle the floor.

It's flat, it's dry and it's concrete. I use my garage to work in all day at the computer and find my feet are freezing after a couple of hours and I imagine it sucks a decent amount of the heat away.

I was thinking some kind of thermal barrier?, with possibly 22mm chipboard on top and carpet tiles? I know carpet seems to be a point of contention for many in a workshop, but i don't mind vacuuming  and it would certainly be more comfortable

I don't fancy the idea of battens/celotex/chipboard, there must be an easier way?

Thoughts?


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## Doug B (17 Oct 2020)

Why not put a floating floor down over 25mm celotex type insulation, no need for battens & you could do it with t&g chipboard glued together.
This is exactly what I’m thinking of doing when the opportunity arises.


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## Fitzroy (17 Oct 2020)

I have an office on the top floor with carpet and in theory a warm floor as it’s the ceiling of a heated room below. By mid day my feet are ice blocks unless I have the house heating turned up, I thick sitting for long periods is a good part of it. I’ve had success with my old down sleeping bag under the desk for my feet and lower legs. Now back to the question. 

Most insulation systems come down to moisture management. Floors are either concerned with damp coming up and getting trapped or water vapour getting down to a cold slab and condensing. You can find out if you have moisture coming up by laying down piece of poly sheet for a few days and seeing if you get moisture underneath. Or if you know the floor construction contained a dpm this is not a concern. Unless you have a good dry, damp proof, slab doing anything without an air gap, ie battens, is asking for trouble.

If it’s dry then a floating floor with a thin foil underlay will help, and the thicker the insulation under the floating floor the better the outcome. Ideally you want a moisture barrier, some materials will act as one, ie T&G OSB with joints glued or Celotex with joints taped. Else I’d put in a layer of polythene on the warm side of the insulation. 

F.


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## craigs (17 Oct 2020)

Fitzroy said:


> I have an office on the top floor with carpet and in theory a warm floor as it’s the ceiling of a heated room below. By mid day my feet are ice blocks unless I have the house heating turned up, I thick sitting for long periods is a good part of it. I’ve had success with my old down sleeping bag under the desk for my feet and lower legs. Now back to the question.
> 
> Most insulation systems come down to moisture management. Floors are either concerned with damp coming up and getting trapped or water vapour getting down to a cold slab and condensing. You can find out if you have moisture coming up by laying down piece of poly sheet for a few days and seeing if you get moisture underneath. Or if you know the floor construction contained a dpm this is not a concern. Unless you have a good dry, damp proof, slab doing anything without an air gap, ie battens, is asking for trouble.
> 
> ...



Thanks for the response,

I was thinking it may have to be celotex+22 T&G chipboard...that stuff is soo damn expensive and winter is coming at the wrong time  

There is a DPM that runs around the edges of the garage internally and the humidity isn't very high surprisingly.

Im definitely taking the the sleeping bag idea, i have an old one here I can rob


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## MorrisWoodman12 (17 Oct 2020)

I extended my partner's shed last year to use as my workshop. It was built with a concrete slab on the ground, then battens supporting a timber floor (not T&G). I had the slab extended then duplicated the battens. Polythene strips over the top of the battens then 18mm MRMDF subfloor bringing everything up to the same level. Covered the whole with 25mm of Celtex then polythene sheeting and 18mm MRMDF flooring panels gluing the edges together. I would have liked thicker Celtex but I needed to preserve headroom even though I'm only 6'. Even now it's only 6' high at the back of the workshop (sloping flat roof). Works a treat even if it's not the 'best' or standard way of doing it.


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## craigs (17 Oct 2020)

MorrisWoodman12 said:


> I extended my partner's shed last year to use as my workshop. It was built with a concrete slab on the ground, then battens supporting a timber floor (not T&G). I had the slab extended then duplicated the battens. Polythene strips over the top of the battens then 18mm MRMDF subfloor bringing everything up to the same level. Covered the whole with 25mm of Celtex then polythene sheeting and 18mm MRMDF flooring panels gluing the edges together. I would have liked thicker Celtex but I needed to preserve headroom even though I'm only 6'. Even now it's only 6' high at the back of the workshop (sloping flat roof). Works a treat even if it's not the 'best' or standard way of doing it.


thats way more work and thickness than i'm looking for, im thinking a weekend job that i can lay something down and move on.


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## Lons (17 Oct 2020)

Hi Craig
You can get Celotex or other brands as cheap as about £12 for 25mm in 2.4 x 1.2 sheets so cheap enough and 18 or 22mm T&G glued chipboard over will do a reasonable job. There are many houses in the Northeast and elsewhere constructed in this manner. I would put down a thin vapour barrier under the polystyrene as a matter of course whether the concrete has a DPM or not, it's very cheap and just belt and braces.
As an aside those houses aren't even faced insulation like Celotex just slabs of white polystyrene.


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## craigs (17 Oct 2020)

Lons said:


> Hi Craig
> You can get Celotex or other brands as cheap as about £12 for 25mm in 2.4 x 1.2 sheets so cheap enough and 18 or 22mm T&G glued chipboard over will do a reasonable job. There are many houses in the Northeast and elsewhere constructed in this manner. I would put down a thin vapour barrier under the polystyrene as a matter of course whether the concrete has a DPM or not, it's very cheap and just belt and braces.
> As an aside those houses aren't even faced insulation like Celotex just slabs of white polystyrene.


I think I'll be doing exactly that, now I just need to find a cheap supplier and get it done .

Cheers


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## MorrisWoodman12 (17 Oct 2020)

Craig. Hi!


craigsalisbury said:


> thats way more work and thickness than i'm looking for, im thinking a weekend job that i can lay something down and move on.


Yes but if you just put down the polythene, Celtex and flooring that's a weekends work. A pretty full weekend admittedly......
Have fun. 
Martin


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## craigs (17 Oct 2020)

MorrisWoodman12 said:


> Craig. Hi!
> 
> Yes but if you just put down the polythene, Celtex and flooring that's a weekends work. A pretty full weekend admittedly......
> Have fun.
> Martin


oh its going to be a PITA, hence easier the better. It will mean putting everything one end, doing half the floor, then moving it all to the other end. opening the garage door is a non starter as its blocked and sealed with a stud wall......probably should have done this before i got the bandsaw and PT :/


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## DBT85 (17 Oct 2020)

I had to do a little of the moving around to do my workshop floor alst week, admittedly there wasn't that much in ther but it was enough to be annoying. But I at least now have 60mm under some 22mm chipboard and its very nice indeed.

My insulation was bought at a farm sale though and cost about £4 for a 4x8 sheet so its not really fair for everyone else!

Unless you're in a major rush, take a look at auctions or seconds to get what you want and save a lot over the rrp.


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## gmgmgm (18 Oct 2020)

craigsalisbury said:


> thats way more work and thickness than i'm looking for, im thinking a weekend job that i can lay something down and move on.


A quick alternative is rubber matting. Look at stable mats or gym floor tiles. I have some of these under my desk and in places where I might stand for extended periods (like anti-fatigue mats).


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## craigs (19 Oct 2020)

gmgmgm said:


> A quick alternative is rubber matting. Look at stable mats or gym floor tiles. I have some of these under my desk and in places where I might stand for extended periods (like anti-fatigue mats).


i didnt even think of that. it might be something to go on top of the chipboard, but i reckon if i put down poly then 25mm celotex followed by 22mm chipboard it might keep the place a bit warmer for longer.


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## Spectric (19 Oct 2020)

When using insulation board it is advisable to tape all the joints with foil tape, excessive gaps use foam first.


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## mrpercysnodgrass (24 Oct 2020)

I have a concrete floor in my workshop, I put down battens then 25mm kingspan then 22mm loft boards. it is a really comfortable floor and my feet never get cold even on days when I'm sitting doing fiddly stuff. It only took a day to put down the whole lot and Im really pleased I did it. Im lucky enough to live just down the road from Seconds & Co Insulation - Nationwide Delivery - Based in Mid Wales They get the rejects from Kingspan which is also just down the road. The reject boards are generally perfect sometimes a bit bashed around the edges, the only thing to watch out for is they vary a little in thickness (I think this is what makes them rejects) which is why on their site they give the thickness as 25mm-30mm etc which is important if you are putting down battens.


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## Cabinetman (24 Oct 2020)

Hi Percy, just curious did you put the installation on the batons or between them?


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