Insulating sectional concrete garage to use as workshop

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Insulating sectional concrete garage to use as workshop

This topic has 11 replies, 8 voices, and was last updated 8 February 2011 at 17:43 by Chris Crosskey.

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2 February 2011 at 17:11 #63423
Chris Crosskey
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@chriscrosskey26628
Hi folks,

The first question I asked on here had a pleasingly high signal to noise ratio in the responses, so I thought I’d wrack your brains rather than ask on general building fora.

I’ve got a sectional concrete garage at the bottom of my garden that I want to convert into a workshop. Currently my stuff is in a 7×11 foot shed I built at my folks place many years ago. Now that the chaos of my moving out is settling (for me anyway) I’d like to make it a priority to get my workshop transferred…. also the folks want the shed….

I’m happy I can damp-proof the floor easily enough (DPM and screed) and reckon that using a polythene membrane on the walls should sort that out but I’m a bit at a loss as to insulation. For choice I’d use 25mm polystyrene behind hardboard on battens on the walls and 50mm ditto or 100mm loft insualtion for the roof. But where to I put the membranes in the wall?… between insulation and wall or between insulation and hardboard or both it’s cheap stuff after all).

To attach the battens to the wall I’ll have to go through the polythene I expect, is it enough to pump silicone sealant into and around the hole behind the polythene and also around the screw/rawlplug? I’m not planning on hanging much weight on the walls, I’ll build freestanding shelving for my stuff.

Also what to do about the roof ?.. It’s a fairly shallow pent and ATM it sufferes condensation, if I insulate the roof where do I put the membrane and I’m assuming it will need ventilating, but into which layer as it were?

Finally are engienering bricks good enough to build a plinth for the lathe and mill on, probably only be a single layer with a levelled concrete top, it’s there to provide a properly flat surface and get the units clear of the flooring (ie they’ll go straigt onto the screen, the insulated and probalby carpeted floor will be around them.

Other folks must have done this so I’m hoping to learn from experiences both good and bad.

Many thanks

chris crosskey
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2 February 2011 at 17:11 #21790
Chris Crosskey
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@chriscrosskey26628
2 February 2011 at 17:25 #63424
JasonB
Moderator
@jasonb
You need a vapour barrier on the warm side of the insulation so in your case it will be under the hardboard(though I would suggest 12mm ply). Polythene will do for this or if you are using one of the rigid insulations like Celotex or Kingspan you can just use foil tape over the joints as the foil covering becomes the membrain.

If you really want to go to town then you can also fit a breathable membrain (tyvek or similar) against the wall and then fit your battens to that but its a bit OTT

Jason
2 February 2011 at 17:30 #63425
Dave Jones 1
Participant
@davejones1
Concrete garages are the new bain of my life. I have one in my new house and although it is prefect against the outside elements it does rain on the inside!

I have not tackled the walls, only the roof and floor. I have a corrugated tin roof, which according to building forums is a nightmare for condensation. I have fitted 25mm polystyrene insulation board inbetween the rafters which seems to work a treat, and stops it raining inside. But make sure there is enough roof for the air to flow above.

As I have a perfectly good concrete floor from the previous owner, I didnt want to raise it any higher with dpm and screed. I painted it with bitumen paint and a few coats of garage floor paint over the top.

Mine is built from concrete blocks as opposed to concrete sections, so I am considering putting a few walls vents in place to improve air flow.

Its not perfect, but a lot better than it was before.

Dave
2 February 2011 at 17:57 #63426
Keith Long
Participant
@keithlong89920
Hi Chris

I’m going to be doing much the same myself in the near future, so looking at the advice
around this is what I make of it – very much echoes what has already been said

1. Try and get some insulation in the floor. If you’ve got the head room 50mm of expanded
poly topped by 100 mm screed will make your feet feel a lot more comfortable, but don’t
ignore the idea of laying a wooden floor either. DPM on top of existing concrete, tanalised
timber on that – you can use fence posts or see what your local fencing/farming suppliers
can come up with. Expanded poly laid between the timber posts and top off with the green
moisture resistant chip board flooring. To give an even better job lay, cheap shuttering
grade ply or OSB over that to give a floor surface thats replaceable, without having to rip
the whole lot up.

2. To kill condensation, you need to keep warm, moist air ie normal workshop air, away from
cold surfaces. So batten and insulate your walls and then lay the dpm on the surface of
that, immediately under you final wall covering if the costs are right I’d personally go for
50mm of expanded poly rather than 25 – you should get the difference back long term in
reduced heating costs. I don’t see any reason why you shouldn’t staple the polythene
membrane to the battens and then cover over the staples with sticky tape but I don’t think
that’s necessary. Fix the wall covering through the polythene to the battens. Personally I’d
think about using plaster board rather than hardboard, it’s much the same price, will stay
flat where hardboard will tend to ripple, and you can hang things on it if you use the right
fixings. You could also use the foil covered plasterboard and dispense with the polythene
layer. You’ll need to do the sums on that to see which is the most cost effective. Finally
paint the wall covering with a good layer of paint to seal it and add another moisture proof
layer – two good coats of emulsion should do that.

3. With the roof I’d follow the same scheme, going from the inside of the workshop, final
covering, dpm, insulation and then ventilation space over that. Again you’re trying to stop
the warm air in the workshop coming in contact with a cold surface

4. If you go with a concrete floor then engineering bricks should be fine, but why do you
want to raise the lathe and mill off the floor? On the timber floor variant work out where
the lathe and mill will come and put extra timber bearers under the floor to take the weight.
then you can just place the lathe and mill directly on the floor over them.
Those are my thoughts – now wait to see other comments.

Keith
2 February 2011 at 18:16 #63428
NJH
Participant
@njh
Hi Chris

I made a workshop in a sectional garage at my previous house and so I suspect you may have a problem getting a fixing for the battens by drilling into the concrete panels. My strategy was to make up some small M/S “U” shaped brackets which could be screwed to the back of the battens. A hole ( or slot ) was made in the wings of the bracket to coincide with the horizontal screw joining two panels. Harder to explain than to do! This worked OK but I think you might achieve much the same result by loosening the bolt off a bit, wrapping a piece of iron wire around the batten then around each end of the bolt. As you say you are not going to hang anything on the wall so the objective here is only to hold the insulation and hardboard ( plasterboard in my case) in position. I used glass fibre loft insulation but I think your idea of polystyrene is probably better – it is self supporting on vertical surfaces. Ceiling height was a problem. I recall that I bought a mill/drill, hired an engine crane to lift it onto its stand and then had to cut a hole in the ceiling to get sufficient height for the jib!

As I think someone said in response to your previous post spend time getting it right now. “Stuff” just grows and grows and you don’t want to be changing your mind in a couple of years time and moving all your kit to get at the walls!

Good luck

Norman
2 February 2011 at 21:14 #63436
Chris Crosskey
Participant
@chriscrosskey26628
Many thanks, all useful info and soem mgood points made that I’d overlooked.

re:@ the plinths… my plan for the floor will have DP then screed then at least an inch of polystyrene plus the green chipboard with industrial carpet over that. But I don’t want my machines sitting on what I consider an unstable base, plus the mill could do with raiisng a bit anyway, it’s a Herbert Simplimill and it’s a fairly compact (though heavily built) horizontal with a vertical attachment as an option…. I could live with it being a foot or so higher….

Anyway, instead of the machines sitting on the chipboard they’ll be on soild plinths from the screed upwards, only one brick layer for the ML7, possibly four or so for the Herbert

chrisc
2 February 2011 at 21:26 #63437
Ian Welford
Participant
@ianwelford58739
Chris

1 think about a dehumidifier and insulate it BUT then don’t use SUDs to lubricate when cutting .

2 put an oil filled radiator on a thermostat in and keep the temp above about 10C and you get less issue with condensation- plus it’s nicer to work in.

3 wood floor is a good idea as if you drop something you don’t damage it as much.

Ian
2 February 2011 at 21:45 #63439
Keith Long
Participant
@keithlong89920
Hi Chris

With the floor, put the dpm down, then the polystyrene and screed over that. The screed spreads the load and the floor is stable. Expanded poly will take a surprising amount of load in compression without complaint. If you have permanent plinths you’ll be a bit stuck if in the future you want to alter the layout to get more “toys” in.

Keith
2 February 2011 at 22:33 #63442
Mark P.
Participant
@markp
My workshop is a 12′ x 9′ steel shed,a few years ago I insulated it by bolting 50mmx50mm battons on the walls, I then put 25mm polystyrene sheet between the battons, I left a 25mm air gap then boarded it over with 12mm OSB. The concrete floor was battoned out with 50mmx25 treated timber,more 25mm polystyerne sheet followed by water resistant chipboard flooring.The roof was covered inside, with more polystyrene sheet,air gap and then hardboard sheets.Result cosy cottage,and fitting shelvs is a lot easier. Cool in summer and warm in winter,and no condensention problems.I also fitted a extractor fan at one end and a closeable vent at the bottom the door at the other to help air flow through the workshop. Hope that this is of help.

Regards Pailo.
2 February 2011 at 23:57 #63449
ady
Participant
@ady
Talking to a client who built houses years ago he was in favour of the foil covering, as opposed to polythene, apparently it was better at keeping out the damp when the insulation membrane was breached by things like nails and electrical wall sockets.
8 February 2011 at 17:43 #63790
Chris Crosskey
Participant
@chriscrosskey26628
Many thanks folk,

I’ve now found another thread that relates to this so will effectively transfer to that one as of now. Many thanks for all the advice and I’ll bear a lot of it in mind as I do my insulation It’s one of the last two big outdoor projects left to go on my house, the 20×10 greenhouse is the other … it’s currently sitting in bits in the workshop shed…..
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