Q&A – Will My Extension Have Condensation Issues?

This homeowner in France built an extension and wanted to know if the approach they took would cause condensation problems. 

Our first international question came from Normandie, France! Grant wanted to confirm that the products used to build their extension were sufficient, asking: 

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, Grant. 

Our resident expert roofer, John Stout with Go Roof Tune Up™, had this to say in response:    

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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Comprised of certified roofing professionals and expert craftsmen with a senior management team of a combined 140 years of roofing experience, Go Roof Tune Up™ is the premier provider of roofing services including repair, maintenance and replacement. Go Roof Tune Up™ inspects your entire roof system, and provides a written report with photos on every property we evaluate. We currently offer services in a number of States and the list is growing regularly. We work with homeowners, real estate professionals, property managers and home investors.