Window Condensation in Spokane Valley

The physics and the humidity targets by outdoor temperature are on condensation on the inside of windows. This page covers the Valley pattern.

The crawl space is the moisture source people never count

When homeowners list where indoor moisture comes from, they name showers, cooking and laundry. In a Valley ranch on a dirt crawl space, there is frequently a larger source than all of those combined sitting directly under the floor.

Bare soil releases water vapor continuously. Stack effect in winter pulls air up out of the crawl space into the house. That air carries the ground moisture with it, distributes it through the living space, and it condenses on the coldest surface available, which is your window glass.

So the sequence is: dirt crawl space, stack effect, elevated indoor humidity, foggy windows. Homeowners run a dehumidifier upstairs and fight the symptom all winter without ever addressing the source.

A ground vapor barrier in the crawl space is frequently the single most effective thing you can do about window condensation in a Valley ranch, which is not an intuitive connection and is why it goes unmade.

The other Valley source: ducts in the crawl

Valley ranch houses typically run their ductwork through the crawl space. Return duct leakage down there pulls crawl air directly into the distribution system and blows it into every room, which is a far more efficient moisture delivery mechanism than stack effect alone.

If your windows fog and the house smells musty whenever the furnace runs, look at the return ducts before you look at the windows. See musty smell when the furnace runs.

Newer stock, tighter envelope

Valley housing skews newer than the city's, and newer construction is tighter. That is good for energy bills and it removes the accidental ventilation that used to carry indoor moisture outside for free.

A 1995 or 2005 Valley house with no mechanical ventilation and a dirt crawl space is a well sealed container sitting on a moisture source. That combination produces more winter condensation than a drafty 1920s house with the same occupants, which surprises people who assume newer means better.

The missing piece is deliberate ventilation: bath fans that actually run and actually vent outside, a range hood ducted outdoors, and in some houses a proper ventilation system. Sealing a house without adding ventilation moves the moisture problem rather than solving it.

What else is collecting water at the same time

If the windows are streaming, so is the rim joist behind the fiberglass, the corners of exterior wall closets, and often the underside of the attic sheathing where indoor air is leaking up through can lights and the attic hatch. The window is simply the surface you can watch.

In a ranch with a lot of single-story ceiling area relative to floor area, the attic exposure is proportionally larger than in a two story house, which is worth knowing if you have been noticing dark sheathing. See attic sheathing discoloration.

What to do

1. Measure with a hygrometer and compare against the target for the current outdoor temperature. Roughly 40 percent at 30 degrees, 35 percent at 20, 30 percent at 10.
2. Turn any furnace humidifier down or off for a week and see what changes.
3. Cover the crawl space soil with polyethylene. This is the Valley-specific high value step.
4. Confirm bath fans and the range hood actually discharge outside, and run them long enough to matter.
5. Check the crawl space ducts for disconnected or unsealed returns.

When to call

When there is growth on the sash, sill or the drywall return around a window. When the drywall around a window is soft or stained, meaning water is entering the wall rather than condensing on the glass. When growth keeps returning after you have corrected the humidity. When closets and corners are affected too. Or when you want the whole moisture picture mapped rather than chasing one symptom at a time.

Blinds, drapes and the air that cannot reach the glass

Condensation forms when the glass is below the dew point of the air touching it, so anything that stops room air from reaching the glass makes the glass colder and the fogging worse. Heavy drapes closed to the sill, cellular blinds pulled all the way down, a valance that seals the top of the window opening: each of these creates a still pocket between the covering and the glass that runs several degrees colder than the room.

That is why the same house can have one window that streams and another that stays clear, with identical glass and identical humidity. It is also why the fogging is worst in the morning, after the coverings have been closed all night. If you have this pattern, leaving a gap at the bottom and the top of the covering, or opening it during the day, changes the surface temperature enough to matter. We note which windows are covered and how before we conclude anything about the house, because otherwise the readings do not add up.

Which windows fog first, and what that tells us

The order matters more than the amount. Bedrooms fogging overnight and nothing else points at occupancy: two people breathing in a closed room for eight hours put a real amount of water into the air, and a closed bedroom door keeps it there. Kitchen and bathroom windows fogging points at fixtures and fans. North facing windows across the whole house points at the envelope rather than any one room. Basement windows fogging while upstairs stays clear points at the crawl space or the slab, not at the windows at all.

We ask for that inventory because it is free diagnostic information you already have. Combined with a humidity reading in each room and a surface temperature at the glass, it usually narrows the source to one or two possibilities before any sampling is considered. And in a good share of Valley houses the answer turns out to be a bath fan that moves almost no air, which is an eighty dollar part rather than anything to do with windows.

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

How can a crawl space cause condensation on my windows? Bare soil releases water vapor continuously, and stack effect pulls that air up into the house all winter. It raises the indoor humidity, and the excess condenses on the coldest surface available, which is the glass. Covering the soil often resolves the window symptom.

My house is only twenty years old. Why does it have this problem? Newer houses are tighter, which removes the accidental ventilation that used to dry older houses out for free. A well sealed house over a dirt crawl space with no mechanical ventilation retains moisture that a drafty house would have lost.

Is a whole house dehumidifier the answer? It manages the symptom. Covering the crawl space soil and ventilating at the sources costs less to install and nothing to run, so it is worth doing first. A dehumidifier makes more sense once the sources are controlled and there is still a residual problem.

Do you cover all of Spokane Valley? Yes, and our office is here. 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.