Window Condensation in Coeur d'Alene

The physics and the humidity targets by outdoor temperature are on condensation on the inside of windows. Three Kootenai County specifics follow.

The low thermostat problem in seasonal homes

This is the Coeur d'Alene pattern that catches owners out, and it is genuinely counterintuitive.

You set a second home to 55 degrees for the winter to protect the plumbing and save on heat. That seems conservative and safe. What it also does is lower the temperature of every surface in the building, including the glass, the exterior wall surfaces, the closet corners and the rim joist.

Condensation happens when a surface falls below the dew point of the air touching it. Lower every surface temperature in the house and you make condensation more likely, not less, at any given humidity level. Meanwhile there is nobody there running a bath fan, opening a door or noticing the windows.

So the vacant house at 55 degrees with no ventilation and a dirt crawl space underneath it accumulates moisture all winter with nobody watching, and the owner arrives in spring to growth on the window frames and in the closets.

What works better: a somewhat higher setpoint than instinct suggests, some deliberate air movement on a timer, a ground vapor barrier if there is a crawl space, and a remote humidity sensor so you know what is actually happening rather than guessing.

Lake and river humidity

Properties close to Lake Coeur d'Alene, the Spokane River and the Coeur d'Alene River have measurably higher local humidity than sites up on the prairie, especially in the mornings and through the shoulder seasons.

The effect is local rather than regional. A lakefront house and a house a mile inland can behave quite differently, and advice written for the region as a whole will not capture that. If you are near the water, the practical implication is that your margin is smaller: the indoor humidity level a prairie house tolerates without condensing may be too high for yours.

New construction, tight envelopes, no ventilation

Kootenai County has built a lot of housing in the last two decades and new construction is tight. Sealing an envelope removes the accidental ventilation that used to carry indoor moisture outside in older houses without anyone noticing.

A tight new house with a family generating several gallons of water vapor a day, no mechanical ventilation, and bath fans nobody runs long enough will fog its windows in January. That is not a defect in the windows. It is a ventilation gap that the tighter envelope exposed.

Newer houses here generally have better windows than the old stock, which means the glass runs warmer and it takes a higher indoor humidity to condense on it. So when a new house does fog, the humidity level behind it is usually quite high, and whatever colder surfaces exist in that house are considerably wetter than the glass.

What else is collecting water

If the windows are streaming, so is the rim joist, the corners of closets on exterior walls, and frequently the underside of the attic sheathing where warm indoor air is leaking upward. In a daylight basement, add the buried uphill wall, which is the coldest large surface in the building and is often finished over.

The targets

Lower as it gets colder outside. Roughly 40 percent at 30 degrees, 35 percent at 20, 30 percent at 10, and 25 percent or lower near zero, for typical double glazing at 70 degrees indoors. Near the water, aim at the lower end of each range.

When to call

When there is growth on the sash, sill or the drywall return. When drywall around a window is soft or stained, which means water is entering the wall rather than condensing on the glass. When growth returns after you have corrected the humidity. When closets and corners are affected. Or when you are opening a seasonal property and found growth in several rooms and want the whole moisture picture mapped rather than cleaning one surface at a time.

Hot tubs and the rooms next to them

An outdoor hot tub is not a moisture problem for the house until it is under a covered patio, in a sunroom, or in a garage or enclosed porch, which is common here. A tub holds several hundred gallons at a hundred degrees, and an uncovered one evaporates a remarkable volume of that water every day. In an enclosed or partly enclosed space, all of it goes into the air and then into whatever is adjacent.

The pattern we see is a house where the windows on one side stream while the rest of the building is normal, with the wall shared with the tub enclosure reading elevated. The cover is usually the whole story. A hot tub cover that has become waterlogged and no longer seals, which happens within a few years in this climate, roughly doubles the evaporation rate. Before anybody talks about the house, that cover is worth checking, and we will say so rather than writing it up as a building defect.

On the glass, between the panes, or on the frame

Three different conditions get described the same way on the phone, and only one of them is about your indoor air. Water on the room side of the glass is condensation from indoor humidity and it is the one worth acting on. Fog between the panes, which you cannot wipe off, is a failed insulated glass seal: the unit has lost its gas fill and its desiccant is saturated. That is a window replacement question and it tells you nothing about your house.

The third is water on the frame and the sill with clear glass, which usually means a thermally poor frame, often older aluminum, conducting cold straight through. That one is worth attention because the water lands on the sill and the wall below it rather than running down the glass, so it soaks into the framing rather than evaporating. We check which of the three you have before doing anything else, because two of them are not the problem people assume they are, and telling you that up front is cheaper for you than a sampling visit.

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

Should I keep my vacation home warmer in winter? A somewhat higher setpoint than instinct suggests generally reduces condensation, because it raises every surface temperature in the building. Combine it with some deliberate air movement and a remote humidity sensor so you can see what is actually happening between visits.

Does being near the lake really change anything? Locally, yes. Near-shore humidity runs higher than on the prairie, particularly in the mornings and shoulder seasons, which means less margin before surfaces reach the dew point. Aim at the lower end of the humidity targets.

My new house has better windows than my old one but fogs more. Why? Because the new house is tighter and retains the moisture that the old one leaked away for free. Better glass actually raises the humidity level required to condense, so a new house that fogs is running quite humid and other colder surfaces are wetter still.

Do you work in Kootenai County? Yes. Coeur d'Alene, Post Falls, Hayden, Rathdrum, Dalton Gardens and Hauser are regular territory, with no trip fee anywhere we travel.