Start where the mold is
- IfLow on a basement wall, in a band or stripSuspect outside water: grading, downspouts, window wells or a foundation crack on that side.
- IfDirectly below a basement windowCheck the window well for debris and drainage, and the window frame or glass block for gaps.
- IfOn a basement ceilingLook upward: kitchen or bathroom plumbing, a toilet wax ring, a tub drain, or an appliance line above.
- IfOn an upper-floor ceiling near an outside wallThink roof, flashing, ice backup at the eaves, or a bath fan venting into the attic.
- IfIn closet corners and behind furniture on outside walls, mostly in winterCondensation from high indoor humidity meeting a cold surface is likely.
- IfAround a tub, shower or bathroom windowPoor ventilation, failed caulk or grout, or a leaking shower valve inside the wall.
- IfIn a cabinet base or under a sinkSupply lines, drain fittings, dishwasher or refrigerator connections.
- IfSpread across a whole basement on many surfacesOverall humidity, possibly from a recent flood that was not dried, or long-term dampness without dehumidification.
Simple observations to confirm a suspect
- Suspected source
- Gutter overflow or downspout
- How to check
- Watch the roof edge during a heavy rain
- What confirms it
- Water pouring or splashing near the damp wall
- Suspected source
- Supply-line leak
- How to check
- Read the water meter with all fixtures off for an hour
- What confirms it
- The meter moves when nothing is running
- Suspected source
- Drain leak
- How to check
- Run the fixture above for several minutes, then inspect below
- What confirms it
- Fresh drips or new dampness after use
- Suspected source
- Seepage through the wall
- How to check
- Tape a square of plastic tightly to the concrete for a few days
- What confirms it
- Moisture under the plastic suggests water through the wall
- Suspected source
- Condensation
- How to check
- Tape the same square; also measure indoor humidity
- What confirms it
- Moisture on the room side of the plastic points to humid air
- Suspected source
- Roof or flashing
- How to check
- Inspect the attic after rain or snowmelt
- What confirms it
- Wet sheathing, drip marks or daylight at the suspect spot
Record what you find
- Date, weather and what you observed
- Photos of the mold and of the suspected source
- Hygrometer readings for the room and outdoors
- Water meter readings if you tested for supply leaks
- Any repairs already done and by whom
- Questions you still cannot answer for the assessor
General information for Hilltop, not a quote or professional advice. In an emergency, call 911.