Which insulation should be used to fix under a metal roof (to avoid condensation)?

Asker: Marc, 52 years old


Dear Marc

Condensation problems arise in insulated roofs because warm air can contain more water vapor than cold air. When warm air, with a high water content through the insulation, diffuses, the temperature decreases closer to the outside, condensing the water that can no longer remain in vapor form in the colder air. This phenomenon happens with all insulating materials through which air can diffuse.

It is therefore important to install an airtight vapor barrier along the warm side of the insulation, in such a way that the warm moist air cannot penetrate into the insulation. This vapor barrier (aluminium or polyethylene) must be applied very carefully, with plastic tape over the seams. Missing or poorly installed vapor barriers are often the cause of substandard insulation, moisture traces in the ceiling and mold development.

The nature of the insulation material matters little because almost all insulation materials allow diffusion of air. PU sheets that are covered with aluminum foil during manufacture are relatively easy to use, because it suffices to apply tape over the seams of the sheets to get the whole thing airtight.

When addressing condensation issues under a metal roof, the choice of insulation plays a pivotal role. It’s essential to utilize insulation that not only offers superior thermal performance but also helps in managing moisture effectively. Different insulation materials come with varied features and benefits, making it crucial to understand common terms and concepts associated with them. For a detailed and informative breakdown of these fundamental aspects of insulation, consider visiting the First Defense Insulation website. This resource will enhance your knowledge, enabling you to make a well-informed decision concerning the most suitable insulation for your metal roof.

Kind regards

Answered by

Prof.Dr. Jacques Tiberghien

Informatics, Telecommunications

Free University of Brussels
Avenue de la Plein 2 1050 Ixelles

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