Garage-workshop conversion - on to the ceiling

[Bert Coules]

I've now lined out the walls of my sectional concrete garage (tile battens, Quinntherm, OSB) and am about to move on to the ceiling. The garage roof is corrugated galvanised steel, not particularly thick, and it's open to the air on all four sides: the gaps between the top of the concrete and the steel are loosely covered by 6"x6" 90 degree steel angle. Here's a pic from before the walls were done:

steel roof suffers very badly from condensation, which obviously I want to eliminate. In a previous thread, the general recommendation was to fit a false ceiling incorporating Celotex or similar (Quinntherm is an equivalent), ideally leaving a complete air gap between the Celotex and the steel. Two questions arise from this:

Would it would be desirable to seal the edges of the false ceiling to the tops of the interior walls, in effect creating a sealed box (apart from inevitable gaps around the door) inside the original garage?

If I use a lightweight ceiling material (I'm thinking of uPVC T&G cladding) could I get away with just sticking it to the foil surface of the Celotex?

Many thanks for any thoughts and suggestions.

Bert

[John Rumm]

Yup - stops warm wet air getting up into cold spaces...

I would have thought so, yes. Quick squirt with expanding foam on the back, prop into position and leave for an hour...

[Bert Coules]

OK, thanks. That should be fairly easy to arrange.

I've never had much luck with expanding foam. And I've never used it as an adhesive - I was think more of a Sticks Like... type of product. Wouldn't expanding foam tend to push the cladding away from the Celotex, unless the propping-up was over the whole surface?

Bert

[John Rumm]

That would work as well...

Not really - it does not expand with much force if constrained. You can get a low expansion version designed for board fixing as well.

[Bert Coules]

Ah, thanks. I might try that.

Bert

[fred]

In article , Bert Coules writes

Absolutely.

Have you decided how to fix the insulation yet?

If not, how about tiling battens on edge, fitted lengthways between and fixed to those deep timber members with the insulation flush fitted between them? Then foam fill, cover with foil tape and screw 3mm ply to the battens to finish, nice & cheap and less work than the tongue & grooving. There will be a minor cold bridge at the battens but I wouldn't worry for a workshop. A temporary counter batten will hold up the insulation while you foam it and save you cutting it for a tight fit.

You could do without the ply but as it is a workshop the insulation will get dinged.

Do I remember you saying you were dropping to 25mm for the ceiling to keep the headroom up? If so then 19x38mm battens on edge would leave a minimum gap to the underside of the roofing of 13mm. It's a light enough structure for this to work. Battens can drop a bit if you stick with the thicker insulation.

Battens at 600mm centres will save the ply sagging but means you'll need to cut the insulation.

Btw, squeezing out lots of sticks like from a shed caulk gun is a bit wearing on the forearms as it's quite thick.

[Bert Coules]

I've arrived at almost exactly the same idea, but - at the higher end of the garage, at least - I have room to lay 1" insulation *above* the battens rather than between them. The battens would be purely to stop the insulation sheet sagging (and I've just seen that you mention this approach later on in your post). Of course I'd have to rely on the weight of the insulation (which isn't much, even in an 8'x4' sheet) to hold it down onto the battens while the foam or other adhesive dried.

Cover the foam-filled gaps, you mean? Will that really make an appreciable difference?

That would be cheaper than the T&G, though I would want to paint it. Individual T&G planks would be a lot easier to work with though. There are advantages both ways: I'll give your idea some thought.

Thanks very much.

Bert

[fred]

Well, over any foam, any joints and the edges of the battens but now that you mention it, it may be a bit of an unnecessary extravagance.

For moisture laden domestic environs it's meant to complete the vapour barrier, maybe not so important for the workshop but it would at least make sure that it's all airtight. It's fairly cheap and the adhesive is guaranteed for long term use, unlike some cheaper duct tapes.

Just floating some ideas in case it helps once you get to grips with the job.

You're welcome