Will my extension have condensation issues?

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December 29, 2022 at 1:09 p.m.


Grant, in Normandie, France, asked:

Hi, I live in France so we get decent summers and cold wet winters and often snow and ice. I have built an extension and have used a metal sheet roof, a foil paper (which turns out not to be waterproof) then 200mm rock wool insulation then 18mm OSB boards then finished with pine boards! My question is would I get condensation issues with only using that style…?

Many thanks,


December 29, 2022 at 1:10 p.m.

Below is what our roofing expert John Stout from Go Roof Tune Up had to say in response to the question:

Thank you so much for the question. Thanks to you, AskARoofer has become a global enterprise. Your sheet metal roof, laid over foil underlay, is an invitation for condensation. Your letter does not describe the attic space, if any. I assume from your question that you are having a problem with condensation. The solution for condensation is air. Lots of air. Is it possible to install air vents in the roof area? If so, fit vents could be installed, and exhaust vents, to pull the moist air out it may/should eliminate the condensation problem.

Thank you for your question.

Your friends at AskARoofer

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