Single walled brick built garage - insulation.

Ok, looking for any/all ideas on this.
Looking to turn my brick built garage into some sort of workshop, it's a decent size and in good condition.
What's the best way of insulating this. It's a piched roof, and it goes straight to tiles underneath, so there's rafters, etc for storage.
Do I put some sort of ceiling on this, I'm a bit worried it will enclose the available space, or do I seal & insulate directly under the tiles in some way ?
Wall insulation, it's a bit impractical to build up a second course of bricks inside (or even outside) to provide a cavity wall, so do I batten and 'double wall' inside with some sort of treated OSB ? What goes in the void ? Is rockwool ok for outside use, is it rot/mildew proof ?
Thanks for any help.
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On 21 Feb 2004 07:17:37 -0800, (Zymurgy) wrote:

I've posted what I did a few times so a Google search will find it. The last time was this past week when there was a thread about fixing Celotex to a wall.
I have a pitched roof with trusses:
- Boarded the roof space on top of the joists over most of the area, but left one centre section with a large, loosely fitted hatch which can be removed if need be to hoist large things up and down. I didn't fit anything underneath the joists where plasterboard would go in a house because it uses space unnecessarily and I didn't want to insulate any more than the boards do at that level anyway.
- Fitted 50mm Celotex to the surface of the rafters using long drywall screws and big washers. Taped over the joins. This leaves a ventilation gap behind which leads to vents added to the soffits. I could have fitted the Celotex between the rafters but that is a lot more fiddly to do.
- Built stud framing using 75x50mm pressure treated timbers, with a timber plate along the floor close to the wall (approx 15mm away from wall at back.). Used DPC material under plate as belt and braces. The vertical studs go between the floor plate and are carriage screwed to the joists above.
- Fitted 50mm Celotex between studs leaving gap behind. This space meets the eaves and is ventilated by the soffit vents. Taped the joints.
- Fitted 18mm ply to the studs using dry wall screws and filled small gaps with PU foam.
- Fitted Celotex sheet to inside of garage doors using Gripfill and a light wooden frame. Fitted ply to inside of doors.
- Painted everything white to maximise light reflection inside.
- Painted floor with 2 part epoxy floor paint. I didn't bother to insulate the floor for height reasons.
- Extended CH from house using separate circuit. I could have used electric heating because the heat loss had been reduced from over 12kW to around 3kW.
- Workshop is now warm and dry year round. The boarding of the floor prevents the warm air rising all the way to the roof so tha tthe lower area is kept warm more easily, but enough warmth rises to keep anything stored in the roof space nice and dry.
I did look at other materials like Rockwool, but Celotex has 4x the insulating properties and is much easier to work with and already has a vapour barrier.. Costs about 15 for a 2440x1220 sheet.
You could use OSB if you wanted, but I got a good deal on buying all the materials from Jewsons as a job lot and preferred the ply.
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