Insulating corrugated garage roof?

19 Jul 2012
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United Kingdom
Hi all,
I want to insulate my garage roof to help stop the condensation. It is a corrugated asbestos roof with wooden joists holding it up.

I was thinking of getting some 50mm kingspan board, cutting it and pushing it between the rafters. Then filling any gaps left from fitting with expanding foam. Would this be good enough and will it stop the condensation problem?

Should i push the kingspan board to the corrugated roof or leave some sort of air gap?

Will i need to add a ply ceiling under the kingspan and tape any gaps to stop any airflow upwards?

I hope allthat makes sense and any advise very welcome.
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I thought i had to stop the warm air touching the cold corrigated roof to stop the condensation?
To have complete success you would need to bond the insulation directly to the roof material and that aint gonna happen with corrugated sheets.
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So am i right in thinking that my only options to get rid of the condensation are:

1. Replace the corrigated roof

2. Use spray on insulation on the underside of the roof?

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