Window Condensation in Spokane

The physics, the humidity targets by outdoor temperature, and what else is getting wet at the same time are on condensation on the inside of windows. This page is about the specific Spokane situation.

New windows in an old house, and why it backfires

This is the single most common version of this call here, and the homeowner is always convinced they were sold bad windows.

They were not. Here is what happened.

An old Spokane house leaked air constantly, through the original double hung sashes, around the frames, through the balloon framed walls, and out through an unsealed attic. All that air movement carried indoor moisture outside continuously, for free, without anyone noticing. The house was dry in winter because it was ventilating itself around the clock.

New windows seal a large share of that leakage. Now the moisture generated inside by showers, cooking, laundry and people stays inside. Indoor relative humidity climbs, and the first cold surface it finds is the glass of the expensive new window.

So the windows did not cause the moisture. They stopped the accidental ventilation that was hiding it. The moisture was always being produced, and now you can see it.

The fix is mechanical ventilation and source control rather than different windows: bath fans that actually run and actually vent outside, a range hood that ducts outdoors, and a humidity level set for the weather rather than for comfort.

Storm windows over original sash

Plenty of Spokane houses still have original single glazed wood sash with exterior storm windows, and that assembly behaves differently.

Condensation on the interior surface means indoor humidity is too high for how cold the glass is running, same as anywhere. But condensation between the storm and the sash usually means the opposite problem: indoor air is leaking past the interior sash into that cavity, and the storm window is not vented. Most wood storms have small weep holes at the bottom for exactly this reason, and they are frequently painted shut. Opening them often resolves it.

If the interior sash is tight and the storm is vented, that cavity stays reasonably dry.

The humidifier that nobody adjusts

A furnace mounted humidifier set once in October and left alone is responsible for a large share of January condensation calls in this city. The setting that felt right when it was 45 degrees outside is badly wrong when it is 15.

The rule is counterintuitive and worth repeating: the colder it gets outside, the lower your indoor humidity needs to be, because every surface in your house gets colder along with the weather. Roughly 40 percent at 30 degrees, 35 percent at 20, 30 percent at 10, and 25 percent or less near zero.

What else is wet in an old Spokane house

If the windows are streaming, so is the rim joist behind the fiberglass, the corners of exterior wall closets, and in many cases the underside of the attic sheathing where indoor air is leaking upward. The window is just the part you can watch.

In a pre-1950 house with uninsulated walls, add the wall cavities themselves, which are colder than in an insulated house and have nothing stopping indoor air from reaching them.

When it becomes a testing question

Condensation alone does not need us. Call when there is growth on the sash, sill or the drywall return, when the plaster or drywall around a window is soft or crumbling, which means water has been getting into the wall rather than just sitting on the glass, when growth keeps returning after you corrected the humidity, or when closets and corners are affected too, which indicates a whole-house condition rather than a window issue.

Old plaster is worth a specific mention. It holds and hides moisture differently than drywall and it can look sound while the lath behind it is not. Moisture readings and thermal imaging answer that without opening it up.

A house built before exhaust fans existed

Bathrooms in houses from the twenties through the forties were built with an operable window and no fan, because that was the code and the practice. Many of those houses still have exactly that. The window works in July and nobody opens it in January, which means every shower puts its entire moisture load into the house with no way out. A single ten minute shower can release the better part of a pint of water, and a family produces several of those a day.

When a fan was added later, it was frequently added badly. The most common version we find is a fan that vents into the attic, sometimes with a duct that points at the roof sheathing and sometimes with no duct at all. That moves the problem rather than solving it and it creates a second problem above the ceiling. The other version is a fan sized for a half bath running in a full bath, moving too little air to matter. Checking that the fan actually exhausts outside, and that it moves enough air to hold a sheet of tissue against the grille, is a five minute test that settles a lot of these cases.

The attic is the same problem, one floor up

If the windows on the main floor are streaming in January, the attic is almost certainly condensing too, and the attic is where it does real damage. Warm humid indoor air rises through every penetration in the ceiling plane: light fixtures, the attic hatch, plumbing stacks, the gap around a chimney, and in these houses the old balloon framed wall cavities that run straight from the basement to the roof. Up there it meets sheathing that is at outdoor temperature.

The evidence is on the underside of the roof boards: frost in cold weather, dark staining where that frost has melted and rewet the same spot for years, rusted nail points. Owners almost never look, because there is nothing to see from inside the house until the ceiling stains. When we get called for window fogging in an older Spokane house we ask to see the attic on the same visit, because the windows are the visible symptom of a condition that is also happening somewhere you cannot see.

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

I got new windows and now they sweat. Were they installed wrong? Usually not. New windows seal air leakage that was quietly drying your house all winter. The moisture was always being produced; it now stays inside. The answer is ventilation and source control rather than different windows.

Should I remove my old storm windows? Generally no. Original sash plus a vented storm performs reasonably well and keeps the interior glass warmer. If you get condensation between the storm and the sash, check whether the storm's weep holes have been painted shut.

What humidity should I run in a drafty old house? The same targets as anywhere, set by outdoor temperature: roughly 40 percent at 30 degrees, 35 percent at 20, 30 percent at 10. A leaky house will often sit below those numbers on its own, which is why it is usually the tightened houses that have the problem.

Is the black growth on my window sill a health problem? On a hard painted surface it is usually straightforward to clean and is not the main concern. What matters more is whether the same conditions produced growth somewhere you cannot clean, such as a wall cavity or a closet.