Musty Basement Smell in Spokane

The mechanism behind a musty smell is the same anywhere, and it is covered in detail on why your basement smells musty. This page is about why City of Spokane houses in particular produce so many of these calls.

The foundations here were not built to be dry

Roughly 27 percent of homes in the City of Spokane were built before 1950, and single family detached houses here average around 70 years old. That is old stock by Western US standards, and it means a large share of Spokane basements are rubble stone, brick, or early concrete block.

Those walls were parged with mortar on the interior and left bare on the exterior, because exterior waterproofing membranes were not standard practice when they went in. A wall like that was built to carry the load of the house, not to act as a moisture barrier, and it passes water vapor continuously whenever there is damp soil against it.

That is the baseline condition in a lot of the older neighborhoods: the South Hill, Browne's Addition, Perry, Garland, West Central, Emerson-Garfield. The wall is not failing. It is doing what it was built to do.

Why you smell it in the bedrooms

Older Spokane houses leak air, and that turns out to matter more than the basement itself.

A heated house behaves like a chimney in winter. Warm air rises and escapes through openings high in the building, and replacement air gets pulled in low, through the basement and the sill. The leakier the house, the more air moves through that loop. So an old Spokane house with balloon framing, an unsealed attic hatch and gaps at every penetration is moving considerably more basement air up into the living space than a modern house would.

That is why the smell shows up on the second floor of a 1920s foursquare and why closing the basement door does nothing.

What we actually find in these houses

• An adjoining dirt crawl area. Very common in Spokane, where a house has a partial basement under the original footprint and a crawl space under a later addition or a porch. The basement is finished and clean, and the smell is coming from the crawl through an open doorway or a joist bay.
• Dried out floor drain traps. Old houses have floor drains that no longer receive water, and the seal evaporates. Free to fix, and worth ruling out first.
• Original coal chutes and abandoned penetrations that were bricked or boarded over without being sealed.
• The rim joist, which in an uninsulated or fiberglass-stuffed old house collects condensation through the winter. See rim joist condensation.
• Knob and tube era finished basements, where somebody framed and paneled directly against a stone wall in the 1960s with no vapor control, and the back of that paneling has never dried.
• Stored material on the slab. Cardboard on old concrete with no vapor barrier under it wicks moisture continuously.

The radon note, because it is specific to this county

Spokane County is one of only three counties in Washington designated EPA Radon Zone 1, alongside Clark and Stevens. Zone 1 means the predicted average indoor screening level is above 4 picocuries per liter, which is the level at which action is recommended.

It comes up here because the pathways are the same.

What to do first

Pour a gallon of water down every floor drain. Get a hygrometer and find out what the actual humidity is down there, not what it feels like. Move everything eighteen inches off the walls and off the floor and look at what was behind it. Pull a couple of rim joist insulation batts on the north and west sides.

Those four cost almost nothing and resolve a real share of Spokane basement calls.

When to call

When the smell outlasts those steps, when it is reaching the living space, when a finished basement got wet and you cannot confirm the wall cavity dried, when you are buying an older Spokane house and the basement smells, or when somebody in the house feels better away from home.

An inspection covers moisture mapping against dry reference readings, thermal imaging, borescope inspection of cavities through a small hole rather than demolition, psychrometrics, and air samples with a mandatory outdoor control taken the same hour.

Painted masonry and the wall that cannot dry

At some point in the last sixty years, almost every old Spokane basement got painted. Usually it was a masonry waterproofing product rolled onto the inside of the foundation wall, sold as a way to stop moisture, and applied over walls that were already damp. That coating changes the physics of the wall permanently. Stone and old concrete handle moisture by letting it evaporate off the inside face. A film on that face stops the evaporation without stopping the water arriving from outside, so the moisture accumulates in the wall instead.

You can read the history on these walls. Bubbling or peeling paint at the base means water is pushing the coating off from behind. A chalky white deposit coming through a crack in the paint means minerals are being carried out in solution and left behind as the water evaporates, which is proof of continuous wetting rather than a single event. We record that pattern and we measure behind it where we can, because the question is not whether to repaint. It is whether the water arriving at the outside of that wall can be reduced, which is a grade and gutter conversation nearly every time.

Why it is worse in July

Owners often expect a basement smell to peak in spring and are puzzled that it is worst in the middle of a dry Spokane summer. The explanation is straightforward once you see it. Summer air is warm and holds a lot of moisture. A basement wall and slab sit at ground temperature, which here is in the fifties year round. When that warm air moves into the basement, whether through an open window, a stairwell or normal air movement in the house, it hits surfaces below its dew point and gives up water onto them.

So the July basement is condensing, not leaking, and opening the windows to air it out is the thing that causes it. That is counterintuitive enough that it is worth testing rather than arguing about, which is why we measure surface temperature and relative humidity together instead of just humidity. If the surfaces are below the dew point of the air in the room, we can show you that on the spot, and the remedy is closing it up and dehumidifying rather than ventilating. It is the most common piece of well intentioned bad advice we correct in these houses.

Pricing

Why an independent tester

Neither Washington nor Idaho licenses mold assessment or mold remediation. The Washington Department of Health states plainly that there are no certification requirements and that anyone can call themselves a mold specialist. New York made it illegal for one company to both assess and remediate the same job under Labor Law Article 32. Nothing like that exists here, which means the company telling you how bad it is and the company selling the fix are frequently the same company.

We test only. No remediation, no reconstruction, no referral fees from the companies that do that work. The report reads the same whether the answer is that your house is fine or that something needs to be opened up.

Frequently asked questions

Is a musty smell normal in an old Spokane basement? Common, yes. Normal in the sense of acceptable, no. It indicates active microbial growth somewhere, and in an old house with stack effect a share of that air ends up in the bedrooms. Common and harmless are not the same thing.

Can an old stone foundation ever be made dry? It can be managed well. Exterior drainage, downspout extensions and grading do most of the work, and interior vapor control and dehumidification handle the rest. Interior sealer paint applied to the dry side generally disappoints because it cannot resist pressure from the wet side.

A short-term test kit costs very little, and the entry pathways overlap with the moisture pathways you are already investigating.

Do you cover the whole city? Yes, all Spokane neighborhoods, and there is no trip fee anywhere we travel. The standard inspection is $425 including one indoor air sample and an outdoor control with lab fees included.