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How can I effectively prevent mold in my mono slant roof style addon with a bathroom in Southern Tennessee climate zone?

Asked by Ernst Lopez
6 months ago
Last Updated: June 4, 2024

Hey there! So, we’ve been working on this roof add-on for what feels like forever thanks to COVID, and we’ve run into some mold issues. The room has a bathroom without dividers, so it’s been pretty open until now. We’ve started getting rid of the mold while building walls and closets, but now we need some advice on how to prevent it from coming back.

Here’s the deal:
– We’re in Southern Tennessee, so keep that in mind for the climate.
– The room has 2×8 rafters with 2×6 insulation r19, all insulated from the start.
– We’ve got ODB, synthetic roof underlayment, and metal roofing.
– The drywall on the ceiling was never fully finished.
– The worst of the mold is above the shower area and in the higher parts of the roof, not so much on the lower side.
– And here’s the kicker – no exhaust vent yet!

Our plan is to ditch the insulation, clean the mold with vinegar, use mold-killing primer, seal cracks with silicone and spray foam, install an exhaust vent fan for the shower, put in new insulation, and add a vapor barrier.

But here’s the thing – is this

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Jociano Nunes

If the bathroom had an open ceiling, that could be why there is mold. The Sheetrock acts as a vapor barrier to prevent moisture from the shower air seeping into the insulation.

Jociano Nunes

The insulation in the picture does not have a vapor barrier to shield it from bathroom steam. It is not designed to be the final ceiling.

Savannah Cooper

Ventilation fan

Savannah Cooper

I didn’t use a vapor barrier, I used greenboard drywall for bathrooms.

Loïc Dumont

The most important thing to do first is to install a vapor barrier. Make sure to staple it up, tape the seams, and then put up the drywall.

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