Window Condensation in Mead

The physics, the targets by outdoor temperature and what else gets wet are on condensation on the inside of windows. This page is about newer north county construction.

Why fogging matters more in a new house

Here is a point worth understanding clearly.

Condensation occurs when a surface is colder than the dew point of the air touching it. A good modern double or triple glazed window has a much warmer interior glass surface than an old single pane, because that is what the insulating value does.

So it takes a substantially higher indoor humidity to fog a good window than a bad one. An old single pane window fogs at a humidity level that is perfectly reasonable. A modern window fogging means the indoor air is genuinely humid.

And if the warmest, best insulated cold surface in your house is condensing, every colder surface is doing considerably worse. The rim joist, the corners of exterior closets, the wall behind furniture, the attic sheathing above a leaky can light. In a new house, foggy windows are a louder signal than they are in an old one, not a quieter one.

The ventilation gap

The reason is almost always that the house was sealed without being ventilated.

A family of four puts several gallons of water into the air of a house every day through showering, cooking, dishwashing, laundry and breathing. In an old leaky house that left on its own. In a tight house it needs somewhere to go, and if nobody built a path, it stays.

The checklist, in order of how often each one is the problem:

1. Bath fans not run long enough. Switched off with the light removes almost nothing. Twenty minutes after the shower is the standard, and a timer switch costs about twenty five dollars.
2. Bath fans venting into the attic. Surprisingly common even in newer construction. Go into the attic and confirm the duct terminates at a roof or wall cap outside the building.
3. A range hood that recirculates through a charcoal filter instead of ducting outdoors, which removes no moisture at all.
4. A furnace humidifier set once and never adjusted. The setting that was right in October is wrong in January.
5. A crawl space with bare soil feeding ground moisture up into a house that cannot vent it.
6. No whole-house ventilation, which in a genuinely tight house is the underlying gap.

The crawl space connection

If your house is over a crawl space with exposed dirt, that is very likely a larger moisture source than everything on the list above combined. Stack effect pulls it up, the tight envelope keeps it, and it condenses on your glass.

Covering the crawl space soil is frequently the most effective single thing a Mead homeowner can do about window condensation, which is not an obvious connection and is why it rarely gets made. See crawl space smell in Mead.

The targets

Lower as it gets colder. Roughly 40 percent at 30 degrees outside, 35 percent at 20, 30 percent at 10, and 25 percent or less near zero, for typical double glazing at 70 degrees indoors. Measure it rather than guessing; a hygrometer costs about fifteen dollars and settles the argument.

Where growth shows up first in these houses

Not usually on the window. On the sash and sill eventually, but before that in the places with no air movement: the corners of closets on exterior walls, behind a headboard pushed against an outside wall, in the corner of a bonus room over a garage, and in the rim joist behind the insulation.

A bonus room over a garage deserves a specific mention, because it is common in this housing stock and it is a difficult assembly. The floor sits over an unheated garage, the walls are often part knee wall with attic space behind, and the room frequently has marginal heating and no return air path. That combination produces cold surfaces with still air, which is the standard recipe.

When to call

When there is growth on the sash, sill or drywall return. When drywall around a window is soft or stained, meaning water is in the wall rather than on the glass. When growth returns after you have corrected the humidity. When closets, corners or a bonus room are affected. Or when you would rather have the whole moisture picture mapped than chase one surface at a time.

Range hoods, make up air and the pressure story

Newer Mead kitchens often have a large hood over the range, and the bigger ones move several hundred cubic feet of air a minute. In a tight house, that air has to be replaced from somewhere, and if no make up air was provided, the house pulls it in through whatever gaps exist. In practice that means the crawl space, the attic, the fireplace, and around the exterior doors. So running the hood for a long bake can pull damp crawl space air up into the house, which then shows up on the windows an hour later.

The same mechanism applies to a whole house fan, a large dryer, and to running several exhaust fans at once. It is worth knowing about because the usual advice for condensation is to ventilate more, and in a tight new house with no dedicated make up air path, ventilating harder can bring in more moisture than it removes. We look at what exhaust equipment is installed, whether there is a make up air provision, and whether the crawl space or attic is the likely donor, because that changes the recommendation completely.

Setting a humidity target you can actually hold

Everyone wants a number. The honest answer is that the right indoor humidity in winter depends on how cold it is outside and how good your windows are, because the whole question is whether the glass surface stays above the dew point. As a working rule in this climate, somewhere around forty percent is comfortable and sustainable in shoulder season, and you have to come down from there as it gets colder, toward thirty percent or below during a hard cold snap. A house that holds fifty percent in January will have wet windows no matter how good the windows are.

The practical step is to buy an inexpensive hygrometer, put one upstairs and one in the lowest level, and watch what the house actually does over a week rather than guessing. Most people find the two readings differ by ten points or more, which is itself the finding. We do this measurement as part of a visit, but you do not need us to start it, and arriving at an appointment with a week of readings makes the whole assessment sharper and usually shorter.

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

My windows are only ten years old and they fog. Are they failing? If the moisture is on the room side and wipes off, no. That is indoor humidity too high for the surface temperature. Fog sealed between the panes that cannot be wiped is a failed glass unit and is a different issue.

Why is my bonus room over the garage always the worst? It sits over unheated space, often has knee walls backing onto attic, and usually has marginal heating and no return air path. Cold surfaces plus still air is the standard condition for condensation and growth.

Do I need a whole house ventilation system? In a genuinely tight house it is the proper answer, though it is worth first confirming the bath fans and range hood actually work and actually vent outside. Those are cheaper and they resolve a fair number of cases on their own.

How do I find out how humid my house actually is? A hygrometer, about fifteen dollars, placed in the room where you see the problem rather than in the hallway. Compare the reading against the target for the current outdoor temperature.