Insullating work shop concrete floor.

[garywayne]

Hi all. It's been a hectic couple of months with crimbo, the workshop build, being interrupted by a kitchen build. Now back to W/S.
I hope everyone out there has been in good health and cheer.

I have decided to insulate my W/S floor which is a concrete slab.

My first Q. At what distances should I have the studding on the floor. Bearing in mind I will have machinery? I will be using 8' X 4' sheets of OSB, or ply as flooring.

Q2. The W/S slab has polythene beneath. I believe I should have DPM inbetween the studwork and concrete. Should there be anything under the insulation?

Q3. Should there be anything between the insulation and the flooring?

Any advice greatly appreciated.
ATB Gary.

 

[MickCheese]

You could consider a floating floor without timbers.

I have seen polystyrene slabs laid down onto the concrete and taped together then 8 X 4 tongue and groove sheets laid on top and glued together. The polystyrene will not compress but don't walk on it without a board.

Mick

 

[PAC1]

Gary

How heavy are your machines and how big/small is their footprint?

Do you intend to move the machines around or will they be in fixed positions?

 

[Dave S]

I did my garage floor exactly as Mick described. Painted the chipboard with garage floor paint and it's brilliant - so much warmer and more forgiving underfoot.

Dave

 

[plug]

I have laid 50mm celotex insusulation on floors before and then lay a floating floor of 22mm p5 chipboard flooring on top.

 

[SVB]

You have two main options really.

A floor on joists as you suggest (some have used 2x4 - therefore 100mm ducting can be run under the floor) or ply over foam.

I followed the second option (see link below) and so far it has worked really well even with 350kg of lathe sat on one end!

https://www.ukworkshop.co.uk/forums/viewtopic.php?t=11826&highlight=

BRgds
Simon

 

[Waka]

Gary

This is what I did with my floor, I laid 2" x 2" joists on the floor (not fixed down), these were 18" apart. In between I laid Xtratherm insulation, on top of this I put down 8' x 2' water resistrant t&g flooring, works a treat.

I have some real heavy machinery on thre floor with no problems at all.

 

[Boz62]

May I ask a question Simon? I'm just working up to fitting a floating floor in my workshop, using T&G MR chipboard in my case. How big an expansion gap did you leave around the edge, and what material did you use to fill or cover it? I'm trying to avoid skirting boards.
Thanks
Boz

 

[SVB]

Boz,

I used T&G marine ply (3/4" if memory serves). I left about 1/4" around the edge and over the past year or so have used shavings and dust to fill it!! (Well, it is only a workshop :lol: ).

BRgds
Simon.

 

[Boz62]

Thanks Simon. Oh well, gives somewhere else for the spiders to hide
Boz

 

[garywayne]

First of all, I would like to thank you all for your replies.

Mick.
I didn't think of a floating floor, but I don't think I would feel comfortable without some sort of solid support beneath my feet. ie, some sort of rafter or studwork.

PAC.
The TS footprint is 500mm X 500mm, and weights 230Kg. All the machinery will be moved around until I am comfortable.

Looking at all the different insulations and prices, the insulation that I am looking at is "Wicks General purpose insulation", which is of fiberglass construction and not solid like the insulation boards. So I would need some sort of framework. Like Waka says, 2" X 2" framework on a DPC with 50mm insulation.

Again, thank you all for your input.

 

[SVB]

Gary,

If you are going for the stud work route, I would really consider 2x4 - and loose the dust extraction under the floor. It would look a really neat job!

Simon.

 

[trousers]

Gary,
fwiw, 2" of wickes gp insulation is very little - even polystyrene sheet has much more insulation value and is really very cheap.
Also, strictly speaking you should have a vapour barrier (1000 gauge polythene) between the insulation and the floorboards, ie on the warm side of the room. This prevents condensation on the floor slab making your 2 x 2's damp.
hth

 

[CNC Paul]

I have laid 50mm celotex insusulation on floors before and then lay a floating floor of 22mm p5 chipboard flooring on top.

Plug's method is excellent, I have a friend who has 25mm polystyrene with 18mm T & G chipboard on top, the floor works really well, he even has an Altendorf panel saw on it without a problem.

 

[white_sw]

I am in the process of insulating my double garage floor. The route I have taken is 25mm x 38mm pressure treated batons,
400mm apart length ways, with staggered batons width ways for extra support. Used no nails to secure them as I didn't want
to risk fracturing the DPC by drilling and plugging. I have then used 25mm polystyrene for insulation and water resistant 8'x4'
18mm T&G chipboard for the floor itself. The floor is secured to the batons with a few screws so it is easy to take up if needs be.
When I have completed this, I plan to give it a couple of coats of a good proxy floor paint.

I've done half and moved my several hundred kg of machines onto it. Planning to do the second half next week.

I would of loved to have a 4" suspended floor, but I can't afford to loose that much height. So for the time being, my extraction
must stay in the rafters.

Cheers,
Sam

 

[Dave S]

May I ask a question Simon? I'm just working up to fitting a floating floor in my workshop, using T&G MR chipboard in my case. How big an expansion gap did you leave around the edge, and what material did you use to fill or cover it? I'm trying to avoid skirting boards.
Thanks
Boz

I left about 15mm all round in a double garage - then had to go around trimming the edges when it expanded to fill the gap!

Dave

 

[trousers]

I reckon you've got a serious damp problem then :shock:

 

[garywayne]

Simon.
Loosing another 2" will be a real niggly little hindrance in the future I recon. Since I done my leg in seven years ago I get really p###ed at the smallest unnecessary inconvenience. So I thought I would put the extraction in the rafters, like Sam.

trousers.
In the Wicks write up they say that the insulation value is nearly double the thickness. So 50mm insulation is the equivalent to nearly 100mm of insulation. (This is not loft insulation. It is for floor as well as other purposes insulation).

regarding the vapour barrier. Is it necessary if I have vapour barrier under the concrete slab? Wouldn't that create damp between the two polythene sheets and rot the floor stud work?

 

[trousers]

Gary

The 'vapour barrier' under the slab is really the damp proof course, ie to prevent damp rising into the concrete slab. If it is intact, all well and good and you do not need to put another one in between the concrete slab and flooring materials.
However, a vapour barrier on the room side of the insulation is designed to prevent airborne moisture in the workshop passing through the insulation and condensing on the relatively cold concrete slab, where your battens may be resting. (The point is that there is no airflow here to remove the moisture).
It's a bit belt and braces I suppose for a workshop cos the amount of moisture in the air in your workshop is only high in certain weather conditions (unless you've got the kettle boiling away all day )
If you used foil faced foam insulation boards (more expensive but much more insulating per cm), and taped the joints and over the joists with foil tape then you would get away without the vapour barrier, as the foil is impervious to moisture.
HTH and sorry if sucking eggs etc.

 

[garywayne]

Thanks trousers for coming back to me on that.

So to make it perfectly clear, (in my own mind).
Inbetween the concrete and the floor joists I put DPC. Within the joists I put the insulation. On top of the joists and insulation I put a polythene waterproof membrane. On top of that, the floor.