# Workshop Roof



## RustyShackleton (15 Aug 2018)

Hi all, I'm planning to replace the pitched roof on a single detached concrete garage, but I'm struggling to get my head around damp proofing and insulation options.

The roof is currently asbestos cement (removal and disposal aren't a concern) and I'm going to replace it with bitumen corrugated sheets (Onduline). The purlins are too far apart for Onduline, so I'm going to fit new timber purlins across the existing metal rafters. I considered decking over the current rafters and purlins with OSB, but would rather avoid the additional expense.

With regards to damp proofing and insulation, Onduline's installation guide says:

"A basic warm roof can be simply formed by fixing purlins onto a roof deck, then lay rigid insulation boards between the purlins, a membrane should be provided to act as a vapour barrier below the deck boards."

Is there any way I can fit insulation without an OSB deck? Either between or below the purlins? e.g. could I fit insulated boards to the metal rafters, then purlins on top of the insulation?

Also any product suggestions? I've seen things like Celotex and they claim to have a built-in vapour barrier - are they a suitable replacement for a separate membrane? For the membrane I was thinking of using Cromar Vent 3 Light.

All I'm after is making the garage into a usable workshop, i.e. tools protected and I won't completely freeze in winter. Looking to keep this as cheap as I can. Any advice would be much appreciated!

Thanks
RS


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