Insulating sectional concrete garage to use as workshop

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

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