# Workshop Insulation and Foundations



## deanflyer (18 Mar 2013)

Hi,

After nearly 5 years I'm finally getting around to moving my tools and woodworking equipment out of the house and into a workshop. Unfortunately I don't have the time to built a workshop, so im getting a 12ft x 8ft shed delivered in about 8 weeks.

Spec of the shed is as follows:-
19mm Tongue And Groove Wall Cladding.
3" X 2" CLS Framework Through Out The Shed.
19mm Tongue And Groove Roof Board Cladding.
22mm Sawn Carcassing Floor Board.
40KG Heavy Duty Green Mineral Chester Felt.

Im minded to put in a proper concrete base. What thickness should the concrete be, suggestions seem to be minimum thickness of 3 inches. A 1m3 of concrete for a 12x8 shed would give me about 5 inch thickness give or take. Would I need any remesh in there for that thickness.

Also, what about heatloss through the floor? Will this be much, or am I better just to put some carpet down, or perhaps a sub-floor?

For a fairly small shed, is it worth the cost of insulating the walls? I wont be spending a lot of time in there, and I will have an electrical feed, so will have a heater installed.

Many Thanks,

Dean


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## carlb40 (18 Mar 2013)

Hi Dean

If it was me. I would mark out where the shed is going. Hire a wacker plate 
http://www.hss.com/g/47428/Vibrating-Pl ... Plate.html

Compact the soil within the marked area. Then put at least 3 inches of hard core down, compact that. Then put 2 inches of sand, compact that. Then put down a plastic waterproof membrane.
On top of that a minimum of 2 inches of polystyrene or similar insulation. 

On top of that i would have a min of 4 inches of concrete. Not sure the mesh will be needed unless it is to be driven on? 

I would insulate the walls if you have space, and definitely insulate the roof space.

EDIT 

I re read your OP and as you have 3 inches of space i would fill the walls with insulation. Foam/ polystyrene will be warmer. Fibregass - cheaper and better for sound insulation as well. Also i would probably ply line the interior to allow hanging of shelving etc where ever you want


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## Mike.S (18 Mar 2013)

Dean 

For my slightly larger shed I did 3" hardcore, sand to blind (just to fill in the gaps) then 4" of concrete but cast in 2 blocks (2 of 6' x 8' in your example) with 10-12mm wooden plank separating - just to act as an expansion joint and avoid the foundation cracking. Still level and sound after 10+ years (on clay soil). I just used a post to compact - wacker plate may save some muscle power. So no DPM or insulation in the foundation - seemed unnecessary to me for a wooden based shed.

One issue I didn't consider sufficiently was the height of the foundation above surrounding soil. Mine's a bit too low - so rain bouncing off soil soaks the wooden base/lower cladding. However, it does make it easier to roll machinery in/out the doors! 

I lined the shed internally using cheap ply/shutter (with glassfibre insulation - value questionable imo) and find this extremely useful for fixing shelves, storage bins/hooks etc. as well as increasing security and rigidity. 

Mike


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## bobscarle (18 Mar 2013)

Hi Dean.

If you are going to use a bought wooden shed then I assume it will have a floor in it. My 8 x 16 shed sits on 6 wooden sleepers which are bedded on gravel and held in place by fence posts set in concrete. There is good air flow under the shed. Over the top of the floor I put underlay then 12mm chipboard sheeting. It could do with a bit more insulation but it is quite warm. It is very rigid.







In the walls I put rockwool then some more 12mm chipboard. Great for screwing to for fixing hooks and the like, although I would find the studs for a shelf.


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## Wood Monkey (19 Mar 2013)

Hi Dean

I did this...

jons-workshop-pictures-t21504.html

At the end you'll see the finished floor. I have to say over boarding the floor was the best improvement I've made in my workshop.

Jon


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## woodray (19 Mar 2013)

My workshop has 4" concrete base with DPC then subfloor with insulation underneath, the walls are clad inside with OSB board with the cavity filled with rockwool the roof is insulated with foam insulation boards I retrieved from builders skips and also lined with OSB which I scrounged from a building site that was clearing up.

My workshop is like toast even in a cold winter and I only have a small tube heater, if you are thinking of leaving a heater on for long periods it would be wise to insulate all round. The cost of insulation will be recouped by the lower energy consumption and if like me you look round building sites there are often some offcuts of thermal board that builders are glad to get rid of.

Most of the cold and damp will come from the base so I advise you to pay particular attention to this area.

Happy woodworking everyone.
Ray


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## the_g_ster (20 Mar 2013)

Inspired by a wooden monkey, i did........

One lot of DPM
One lot of 50mm XtraTherm board
One lot of 22mm P5 moisture resistant board

Now I have one toasty workshop.

I already had a sound yet very old concrete base, that luckily was lower than door entry height.

If you insulate BELOW the the slab, you will have more thermal capacity in the slab, eg, once it's warm it will stay warm for a while. So if you think you'll maintain heat in there, it is worth it.

If like many of us you are time stretched and just use your shop when you can, I would insulate over the slab. That way quick to warm up.


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## deanflyer (21 Mar 2013)

Thanks for all the info. As I wont be spending too much time in there, I think I'll go for a standard concrete base with DPM and insulate the floor.


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## deanflyer (21 Mar 2013)

More questions 

The shed im buying has a ventilation gap, see below:-






Is this normal. I know there should be some ventilation, but this looks quite a lot.

Also, when they deliver it, would it be feasible to insulate the base before building it. As it's an 8 x 12 im assuming they build off site and just drop off and assemble. 

How do you insulate the base without it getting damp, surely if you put a DPM/Visqueen type covering on top of the concrete and then put Kingspan etc. on top of that you would get damp inbetween the two layers?


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## carlb40 (21 Mar 2013)

No that is not normal as such. If you built this yourself, you would have the roof joists overhanging the walls slightly or a lot depending on how you want it to look. You would the put timber on the face and under to form a fascia and soffit detail. In that you would put a couple of vents.

The dpm is to stop rising damp. Depending on the height inside i would probably wait until the shed is up, then insulate.


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## deanflyer (21 Mar 2013)

Thanks for that. Here is a link to a smaller 6 x 4 Pent that the company does, so similar construction. 

http://bit.ly/102UYB3

Dean


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## carlb40 (21 Mar 2013)

If the roof detail is the same/similar then they have already created the detail i mentioned. So all you need to do is cut/fix ply or cladding to the underneath of the roof joists. Plus fit a few vents or get a strip of soffit vent from a builders merchant and use that


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## deanflyer (28 May 2013)

okay, the shed is finally up  will try and put some pics on at some point.

Looking at insulation for the walls and there seems to be a lot of choice. Bearing in mind I'm only going to be working in the shed a couple of hours at a time, is it worth going for something like Celotex boards, or is there a cheaper alternative. I dont want to go polystyrene because of the fire hazard. The wall joists are 40mm with 22mm tongue and groove cladding. I'm not too keen on battening out the internal space as its small enough already.

The floor has timber boards sitting on top of the joists, sitting on the concrete foundation. The joists are 40mm so some airflow will come underneath the shed. Was thinking of putting 20mm of rigid insulation (any suggestions) and then some 6 or 9mm ply on the floor. This sound okay?

The roof has tongue and groove boards, with roofing felt on top. Is it okay to put a roofing barrier on the inside then insulation, or would I be better taking off the roofing felt and putting a barrier on then roofing felt (should have asked the builders to do this)?


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