How to find and handle hidden mold behind walls
Hidden mold behind drywall requires immediate verification and remediation, but sealed walls prevent you from accessing the opening to check the severity. Without knowing the next steps, homeowners panic about safety and air quality while trying to decide whether invasive repairs are truly necessary.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from October 2026.
- This comes up 11.3× more often in r/HomeMaintenance than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
How to find and handle hidden mold behind walls
- 1Close the door and leave the exhaust fan on with a towel by the base of the door while sleeping in a different room.Did this help you?
- 2Choosing to let the issue ride and ignoring it unless moisture visibly presents itselfDid this help you?
- 3Accepting higher heating bills for drafty rooms rather than tearing apart finished spacesDid this help you?
- 4Cutting open drywall to visually inspect stud baysDid this help you?
- 5Air sealing gaps and insulation around window framesDid this help you?
- 6Applying caulking and checking exterior flashingDid this help you?
- 7Using home mold testing kitsDid this help you?
- 8going to the doctorDid this help you?
- 9getting mold testingDid this help you?
- 10having the ventilation fan inspectedDid this help you?
- 11walking the house twice a yearDid this help you?
- 12checking every line of caulk and siliconeDid this help you?
- 13pulling curtains back to inspect window framesDid this help you?
- 14opening sink cabinets to check for smells and dry P trapsDid this help you?
- 15pouring water down unused drainsDid this help you?
- 16buying over-the-counter mildew sprays or cleanersDid this help you?
- 17asking friends or family members who do home renovations for their opinionDid this help you?
- 18getting the mold tested to verify the typeDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I have no clue what the next steps are and quite frankly I’m panicking that we’re breathing in the black mold since we’re sleeping here and this is the only bathroom. I’m a first time homeowner and I need help!”source ↗
“My wife swears she smells mold in my son’s room at night when his door is closed.”source ↗
“To appease her I took off the aluminum sill and obviously cut a hole in the wall. I don’t see mold and the wood is dry.”source ↗
“Verification is part of the problem because I have no access to the opening.”source ↗
“There does appear to be some growth that starts approximately at the knee wall. Is this something that should be remedied even though it will be somewhat invasive or is this something to let ride?”source ↗
“instead of getting better we've been getting worse, we thought his allergies to the dogs were making him worse and ive had a sinus infection so we didnt question it too much.”source ↗
“today I went into the bathroom about 2 hours after he took a bath and the bathroom reeked of ammonia.”source ↗
“popped the vent off and discovered tissues STUFFED into the vent, started pulling them out and realized this is probably why we've been getting sick.”source ↗
“we've been slowly dying in our own home, and have no idea who even caused the issue.”source ↗
“we work healthcare so I shower every night, and he takes a bath every morning and night, so we've been unknowingly exposing ourselves to mold and bacteria for hours a day for 3 weeks.”source ↗
“That is definitely active mold, not mild mildew. Do NOT trust that family friend's advice he is downplaying a real issue”source ↗
“man i did this last month and found a softball sized mold patch behind the couch where the baseboard was pulling away from the wall. the couch has been in that spot for three years. never moved it once.”source ↗
“I'm very sure that the back door to my parents house has a rotted piece of wood under it.”source ↗
Where this came up
People with this problem also raised
- 27How to clean mold on furniture after rain gets inside
- 31Water dripping from electrical switches behind walls
- 4How to tell if mold is hiding after a roof leak
- 13How to clean mold on drywall or know when to cut it out
- 2Horizontal crack behind basement paneling: how worried should I be?
- 5White cottony growth on basement wall mold or mineral deposits?