1. A musty smell you cannot locate
The most reliable indicator, and the one people dismiss the longest. That earthy, damp-cellar odor is microbial volatile organic compounds — gases produced by actively growing mold. If you can smell it, something is growing. In Clark County the source is usually below the floor rather than on a wall, which is why nobody can find it by looking around the room.
2. The smell gets stronger when the heat kicks on
This one narrows it down fast. If the musty odor arrives with the furnace, your ductwork almost certainly runs through the crawl space and has separated somewhere, so the system is pulling crawl air into the house. Extremely common in the postwar ranches across Hazel Dell and similar mid-century housing.
3. It gets worse from October and better in July
A seasonal pattern is diagnostic. Vancouver's wet season runs October through May and July is genuinely dry, so a moisture problem tracks the calendar precisely. If the smell, the symptoms, or the stains follow the rain, you are looking at a moisture problem rather than a one-time event.
4. Symptoms that improve when you leave the house
Congestion, a cough, itchy eyes, headaches, or asthma that eases within a day or two of leaving on a trip and returns within hours of coming home. This is worth taking seriously, and worth mentioning to your doctor as well as to a remediation pro.
5. Condensation on windows every morning
A little on the coldest mornings is normal. Water running down the glass and pooling on the sill most days means indoor humidity is too high, and if it is high enough to condense on the window it is condensing inside walls too. Original single-pane sash windows in the Hough and Arnada bungalows do this readily, but a modern window doing it is a clearer warning.
6. Dark spots in closet corners or behind furniture
Growth on an exterior wall where air does not circulate. Very common in tight newer homes in Orchards, Fisher's Landing, and Ridgefield, where indoor humidity accumulates and finds the coldest surface. There is usually no leak; it is condensation.
7. Floors that are cold, clammy, or springy
Cold floors in winter suggest crawl space insulation that has fallen or absorbed moisture. A soft or bouncy spot means the subfloor or a joist may have been wet long enough to lose strength, which is a structural conversation as well as a mold one.
8. Hardwood that has cupped
Boards curling up at the edges means moisture is coming from underneath — the classic signature of a wet crawl space beneath a hardwood floor. Cupping shows up long before anything is visible from above.
9. Peeling paint, bubbling drywall, or lifted baseboards
Finishes fail where moisture has been sitting behind them. A tide line a few inches up the wall, wallpaper releasing at a seam, or trim that has separated from the wall all indicate water in the assembly, not just on it.
10. Staining on the attic sheathing
Grey-black discoloration on the underside of the roof deck, usually concentrated on the north-facing plane. In this region it is almost always condensation rather than a leak, and it is one of the most frequently written-up findings in Vancouver home inspections. Worth a look with a flashlight before you list your house rather than after.
11. A pest problem you did not have before
Damp wood attracts carpenter ants and other moisture-loving pests, and wet fallen insulation is ideal rodent nesting material. In Clark County, a new rodent or ant problem under the house and a crawl space moisture problem show up together often enough that experienced pros check for both automatically.
12. Moss on the roof and a north side that never dries
Not mold itself, but the outdoor half of the same story. Heavy moss holds water against shingles and works under the courses, keeping the deck cold and damp while interior condensation works on it from below. Under mature firs in Cascade Park or Felida, a north roof plane may see almost no direct sun for months.
What to do next
If you have two or three of these, the next step is not to start tearing things out. It is to find the water. Get a flashlight and a mask and look in the crawl space and the attic yourself, or have someone do it — free assessments are standard in this market. Do not disturb visible growth before it is contained; scrubbing a dry patch releases an enormous number of spores and can turn a one-room problem into a whole-house one. And if you can already see the mold and you know where the water came from, you can usually skip testing and go straight to fixing it. Our inspection and testing page explains when a lab result is actually worth paying for.