CeeJay Posted January 5, 2011 Share Posted January 5, 2011 Apologies but this is a regurgitated posting as I fear the original got lost at the back end of another posting!I have just converted the grenier and now need to insulate the exposed roof.I have in mind to fix extruded polystyrene blocks of 40mm thick between the rafters, which are roughly 80mm square and about 450mm apart then cover the lot with plasterboard but still exposing the 3 large beams.I would appreciate advise as to whether it is necessary to put a vapour barrier in before I fix the plasterboard and would it be sufficient to pin up a plastic sheet as a barrier or would I need to buy the plasterboard with the vapour barrier already affixed?Apologies for the size of photo, my first use of Photobucket!!!!I have in mind to fix extruded polystyrene blocks of 40mm thick between the rafters, which are roughly 80mm square and about 450mm apart then cover the lot with plasterboard.I would appreciate advise as to whether it is necessary to put a vapour barrier in before I fix the plasterboard or if foil backed board would be sufficient. If this is so what is the French name for this type of board?Apologies for the size of photo, my first use of Photobucket!!!! Link to comment Share on other sites More sharing options...
CeeJay Posted January 5, 2011 Author Share Posted January 5, 2011 Sorry, should have deleted the bit below the photo!!!! Link to comment Share on other sites More sharing options...
pachapapa Posted January 5, 2011 Share Posted January 5, 2011 [I] Link to comment Share on other sites More sharing options...
Théière Posted January 5, 2011 Share Posted January 5, 2011 CeeJay, you must have an air gap as well as a membrane. Try to go thicker than 40mm or use a multifoil as well, something lke Actis which is made in France. Link to comment Share on other sites More sharing options...
CeeJay Posted January 5, 2011 Author Share Posted January 5, 2011 Theiere, thanks for the reply.I thought that by specifying 40mm polystyrene within an 80mm gap that would be sufficient air gap between the insulation and the roof, are you saying that the air gap needs to be between the plaster board with vapour barrier and the insulation? Link to comment Share on other sites More sharing options...
Théière Posted January 5, 2011 Share Posted January 5, 2011 You don't need an 80mm air gap you only need 25mm or so and add more insluation. The guide should help with the explanation. Also several more good ideas on This site from Just John's post. The idea is to allow ventilation for removal of moist air whilst sealing the room from drafts of air. The test in modern houses is to pressurise them to a certain point and they shouldn't leak. Link to comment Share on other sites More sharing options...
CeeJay Posted January 5, 2011 Author Share Posted January 5, 2011 TheiereOnce again many thanks for much useful information and I am now a lot clearer in my mind on the way forward. Link to comment Share on other sites More sharing options...
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