How to insulate a flat roof?

21 Aug 2007
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United Kingdom
For one reason or another we now have a 3.3m x 3.6m flat roof on the extension which has no ceiling, no insulation etc. You look up and you can see the rafters and the decking. We had a major leak and large part of the ceiling colapsed during the redeck and reroof, so I just finished the job pulling the lot down.

The insulation that was in there was 1" of fibreglass which has probably been in there since the early 70's.

There isn't any planned ventilation under the decking so I was concerned about what insulation to use. I was originally thinking of foam spray but I'm now concerned about it's problems having used the search on here!

The rafters are 6"x2" spaced between 14.5" and 18" in a random pattern so I think lots of cutting of insualtion with anything. The ceiling height is already very low so we cannot insulate under the rafters.
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