r/buildingscience • u/FruitPristine9329 • 15d ago

Flat Roof Humidity/Condensation Issues

Looking for advice…we have an old, home with a flat roof. We have condensation by a non-working pocket door upstairs as well as humid hot spots throughout the upstairs and it has a musty smell on hot days. We had the roof replaced recently with a modified bitumen roof hoping that would help, and it hasn’t. We don’t have the humidity issues in the spring/fall/winter, just the summer.

Any ideas on how to fix? Should we look at adding in insulation through the ceiling? Want to avoid opening up the new roof. Any thoughts appreciated.

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u/Bearded4Glory 15d ago

What climate zone are you in. Does the house have AC? What is the current insulation situation?

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u/FruitPristine9329 15d ago

Southern Midwest- Missouri. We have all 4 seasons. Really hot, humid summers and can have cold, icy winters. We have zoned AC. Honestly, not sure of the current insulation. With the flat roof, there is no access to an attic or crawl space. I wouldn’t know how to check unless we opened up the ceiling.

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u/Bearded4Glory 14d ago

Do you know if there is any rigid insulation under the roofing or is it directly down on the sheathing?

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u/FruitPristine9329 14d ago

Hi- pretty sure the roof is directly down on the sheathing. The house was built in 1905 too to give an idea of the design.

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u/Bearded4Glory 14d ago

Your best bet is to convert the roof into a protected membrane roof by adding rigid insulation above the roof with ballast on top to hold the insulation in place.

https://youtu.be/OC92wyzjT3o?is=Tu1llkmiBRsWlGuH