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We returned home after the holidays and saw that the ceiling in our upstairs bedroom has been discolored. I checked with the moisture meter and it showed a "100% wet" reading, but only in a relative small area (less than 1 ft radius). I climbed into the attic with a measuring tape, located the exact spot, and dug my hand into the blow-in insulation. To my surprise, everything seems completely dry. I also tested all wood beams and they indicated no excessive moisture either.

Then I saw a dark lump at exactly that location, which seems to be tar from the shingles that has melted and descended into the attic. That could explain the brown color, but it was completely solid due to the cold. Also, I don't understand how it could have melted recently given the current winter temperatures (in the summer, by contrast, it gets really hot here).

What is the cause of the brown spot on our bedroom ceiling? I don't want to treat the symptom by painting it over until I know what the root cause is.

You can see the photos I took here: https://imgur.com/a/5d6m124

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  • Umm... tar from shingles, or feces from rodent? Rather obnoxious test: try melting that "tar" on a disposable foil pan -- tar melts, feces won't. Also consider danger, e.g., cdc.gov/hantavirus/index.html
    – DrMoishe Pippik
    Commented Jan 1 at 17:20
  • Thanks for the responses. One question, though: if this is really feces, why does the moisture meter indicate 100% in that area? Or is that moisture caused by the feces?
    – Gganbu703
    Commented Jan 1 at 17:50
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    Ah... delicate subject.... what might issue along with feces?
    – DrMoishe Pippik
    Commented Jan 1 at 20:07

1 Answer 1

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As stated by others, this is most likely waste from some animal. The liquid (urine) seeped into the drywall and made a stain and peeling paint.

Treat the area in the attic with some spray disinfectant, after removing any solids.

Scrape away the loose paint, treat the area inside with a stain sealer and repaint.

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