INSULATING OUTBUILDING ROOF

[CURLEW]

Dear All,

I want to insulate my outbuilding roof. The roof consists of (new) corrugated iron on wood rafters. It is not a flat roof and has a gentle incline.

The problem is that on cold days/nights frost forms inside the building on the underside of the corrugated iron and then melts as the temperature raises, soaking everything in the building.

What I was thinking of doing was buying insulating plasterboard, sticking a polythene covering on the topside of this and boarding the roof leaving the requisite gap between the roof and the plasterboard for free flow of air. First thing, do you think this is a good idea? Secondly there is bound to be still some condensation between the tin roof and the plasterboard and therefore, will the boarding just become soggy and rot?

Help!

Thanks,

Curlew

 

[noseall]

problem is, sounds like you're heating a space with a totally inadequate roof covering. unless you insulate the roof correctly ( min 130mm kingspan/celotex complete with vapour barrier,vents etc) then you will only compound the problem, and end up with a nasty fungus!

 

[masona]

Ideally would be to remove the corrugated sheets put down roofing felt then refix the corrugated sheets on top so any condensation would be collected onto the felt and straight out to the gutter.

On my summerhouse I used moisture resistance T&G chipboard then roofing felt with roofing sheets on top and never has any problem although you don't have to use chipboards if you don't want to but it does mean you can fit the sheets fixing anywhere on the chipboards and looks better underneath. There's also nothing to stop you adding another suspended ceiling underneath for extra warmth.

 

[CURLEW]

Thanks Noseall and Masona for your responses.

The outbuilding is essentially an eighteenth century structure which has had a tin roof put on. As with most outbuildings in Cumbria it isn't heated and that obvously is part of the problem.

The suggestion of the roof felt would be a good idea but the roof has been cemented down round the edges and would cost too much to take off and relay.

I think I am going to have to go with in effect a false ceiling made of insulation boards. Thanks for the details on these.

Regards,

Curlew