Mold From Hidden Leak in Mission Hills, San Diego

An air test in a Mission Hills home in San Diego showed elevated mold spores in a bedroom and bathroom. The cause was a disconnected bathtub drain emptying under the house; after the repair we removed the saturated drywall under containment, treated the framing and dried it.

Project at a glance

Location: Mission Hills, San Diego
Signs: elevated mold spores on an air test in a bedroom and bathroom; drywall near saturation
Cause: disconnected bathtub drain discharging into the soil under the house
Inspected: walls, floors, crawlspace and the plumbing access panel
Work: containment with HEPA air filtration, removal of saturated drywall, cleaning and treatment of the framing, drying
Date: July 2026

What we found

An air test in a Mission Hills home showed elevated mold spores in a bedroom and bathroom. We inspected the walls, floors, crawlspace and the plumbing access panel. Running water in the tub revealed the cause: the bathtub drain was disconnected, so used bathwater went straight into the soil under the house. That moisture rose into the sill plate, subfloor and framing and wicked up into the drywall, which read near saturation.

What we did

Waited for the drain to be repaired before starting, so the source was stopped.
Set up containment with HEPA air filtration.
Removed the saturated drywall.
Cleaned and treated the framing.
Dried it with professional equipment.

Result

With the drain fixed and the saturated materials gone, the framing was cleaned, treated and dried.

Photos from this project

Damage at the base of the wall
The cause: a disconnected tub drain
Saturated drywall removed
Drying the bathroom under containment

Questions homeowners ask

Can a leak under the house cause mold inside the walls?

Yes. Water in the soil or crawlspace raises moisture in the sill plate and framing, and it wicks up into the drywall. The fix is to stop the leak first, then remove the wet materials and dry the structure.

Why did the air test show mold when no water was visible?

The leak was under the house, not in the room. Moisture moved up through the sill plate and framing into the base of the walls, where mold grew out of sight. Elevated spore counts on an air test are a signal to look for hidden moisture with meters, not only for visible growth.

How do you find the hidden leak behind a mold problem?

We measure moisture in walls and floors, check with a thermal camera, inspect the crawlspace and access panels, and run the fixtures. In this home, running the bathtub showed the drain was disconnected and emptying under the house.

Can a bathtub drain leak without water showing in the bathroom?

Yes. If the drain pipe below the tub disconnects, the water goes into the space under the floor instead of the bathroom. Warning signs are a musty smell, peeling paint or soft drywall at the base of nearby walls, and a damp crawlspace.