Key takeaways
- Spokane's summers are dry, but winter condensation and spring snowmelt bring plenty of moisture into houses.
- Attics get mold when warm, damp house air leaks up and condenses on the cold roof deck.
- Crawl spaces and basements get mold from snowmelt and runoff near the foundation, bare soil and leaks.
- Older homes with stone or early concrete foundations let more moisture through.
- Most prevention is cheap: fans vented outside, gutters and downspouts working, a vapor barrier, indoor humidity in check.
People who move here from Seattle or the coast sometimes assume Spokane is too dry for mold. The summers are dry. But mold only needs a damp spot that stays damp, and a Spokane house gets plenty of those between November and May.
Attics: the winter problem
On a January night the roof deck can sit well below freezing while the house below is at 68 degrees, full of moisture from showers, cooking, laundry and breathing. Warm air rises and slips through any gap in the top-floor ceiling: recessed lights, the attic hatch, plumbing stacks, wiring holes, the gap around a chimney.
When that air hits the cold sheathing, the moisture freezes into frost on nails and plywood. It melts on the next warm day and soaks into the wood. Over several winters, that’s how you get the gray and black staining that home inspectors flag on so many local attics.
What helps:
- Make sure bathroom and kitchen fans vent outside through the roof or wall, not into the attic
- Seal air leaks in the ceiling below the attic, especially around lights and the hatch
- Keep soffit vents clear of insulation so outside air can move through
- Add insulation where it’s thin, after air sealing
Crawl spaces: spring runoff
When the snow melts, all that water goes somewhere. If the yard slopes toward the house or downspouts dump right at the foundation, a lot of it ends up under the house. Add bare soil with no vapor barrier, and the crawl space stays humid for months. Joists and subfloor start growing mold, usually lighter in color than people expect.
What helps:
- Downspout extensions that carry water several feet from the foundation
- Soil graded away from the house
- A ground vapor barrier, overlapped and sealed at the seams, with no torn sections
- Checking the crawl space once a year, ideally in spring
Basements: older foundations
Spokane has a large stock of older homes, especially in neighborhoods like the South Hill, Browne’s Addition, West Central, Logan and Hillyard. Many have basements with fieldstone, brick or early poured concrete foundations. They let moisture through more readily than modern foundations, and a basement finished decades ago may have drywall or paneling sitting directly against a damp wall.
What helps:
- A dehumidifier, especially from spring into early summer
- Keeping stored boxes and furniture off the floor and away from exterior walls
- Fixing grading and gutters, the same as for crawl spaces
- Being careful about finishing a basement that shows signs of moisture
Everything else
Windows that stream with condensation every morning, a washing machine hose that drips, a toilet seal that leaks into the subfloor, a humidifier running too high. None of these is unique to Spokane. They add up, and they’re easy to check.
If you’ve already found mold, prevention comes second. Get the growth cleaned up properly first. Our pages on attic mold removal and crawl space mold explain what that involves, or you can request a free inspection.
Frequently asked questions
What indoor humidity should I aim for?
EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. In a Spokane winter, very high indoor humidity is also what drives window condensation and attic frost.
Should I run a dehumidifier in my Spokane basement?
If the basement feels damp or smells musty, or a cheap hygrometer reads high, a dehumidifier helps. Many basements here need one mostly in spring and early summer.
Is frost in my attic normal?
A little after an extreme cold snap can happen, but regular frost on nails and sheathing means too much warm, moist air is getting into the attic. That's the setup for attic mold. Have the ventilation and air sealing checked.
Do newer homes get mold too?
Yes. Tighter houses hold more moisture inside, and a bathroom fan that's undersized or ducted into the attic causes problems in a five-year-old house as easily as an old one.