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I am having a strange issue wherein along the exterior/west-facing wall of my bedroom (~110sqft/750sqft house) at the junction with the ceiling there appears to be mold growing and some pretty faint water stains. There is no plumbing above and the house water main/ a hose bib beneath is beneath this room but there are no leaks that I can see in the crawlspace. Up in the attic there is absolutely 0 sign of water incursion or leakage from the roof. The only notable thing is that towards the eaves the insulation does not seem to be as thick as the rest of the attic (blown in cellulose insulation).

Image of the problem area: enter image description here

Image showing the condensation: enter image description here

Image of the attic: image of attic

Humidity generally runs high in this room for some reason. Higher than the rest of the house as far as I can tell. I first noticed this very light mold 10 months ago (moved in 12 months ago) and cleaned it off with vinegar + got a small dehumidifier for the room. Over the spring and summer it was fine. To get the humidity really in check, I think that a bigger dehumidifier would be needed. It is the only room in the house that often has condensation on the windows and now I have noticed there is a bit of condensation where the mold is growing (as pictured above).

The attic is not particularly well vented (end vents & 4-5 ridge vents.)

Any ideas what could be causing this? Solutions?

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  • Do you have soffit vents? Or just the vents you mention?
    – Ecnerwal
    Nov 30, 2023 at 0:52
  • No soffit vents, just the gable and ridge vents. Nov 30, 2023 at 17:28

1 Answer 1

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The area being exposed to cold air above will encourage condensation from the inside air.

You need more insulation, or baffles to keep the insulation out of any soffit vent we can't see, and then more insulation right up to that baffle.

If you have what appears to be perhaps 4" of cellulose, (barely up to what appears to be a 2x4, where present) more insulation of the whole attic will help your energy costs a bunch, AND reduce the condensation issue here.

That won't help with the wetness if you're wrong about the roof staying dry, of course. But if it's condensation and not a leak, it will help a lot.

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