Insulation on flat roof: between rafters or under felt?

[Deleted User] · 2017-09-21 08:34:55

The builder asked me where would we like to put the insulation for the flat roof over the room we are converting. Apparently, the choices are to put it between the rafters (or is it joists?) or under the felt itself. Where is best to put it? Thanks.

21-09-2017 09:34AM

#1

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The builder asked me where would we like to put the insulation for the flat roof over the room we are converting. Apparently, the choices are to put it between the rafters (or is it joists?) or under the felt itself.

Where is best to put it? Thanks.

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#2 21-09-2017 07:21PM

budhabob

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Go with rigid board insulation under the felt (cold roof). If you go between the rafters (warm roof) there's a risk of moisture build up and dampness. Also 100mm rigid board insulation would be better than the insulation usually used in between the rafters.

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