A foggy window in January could mean your windows have failed, or it could mean your house is doing something completely normal for a Pacific Northwest winter. The two look similar from across the room and they have nothing to do with each other. One is a free fix involving a bathroom fan. The other means the glass unit is finished.
The wipe test settles it in three seconds
Walk up to the window and try to wipe the fog. There are only three places the moisture can be, and each one means something different.
Fog on the inside surface that wipes away is condensation. Warm moist indoor air is hitting the coldest surface in the room and giving up its moisture. Your windows are behaving exactly as glass behaves. It is still worth addressing, because water sitting on a sill every night rots trim and grows mildew, but the window is not defective.
Fog on the outside surface is good news, oddly enough. Exterior condensation on a cool clear morning means the outer pane is staying cold, which means the coating and the insulated cavity are keeping your heat inside rather than bleeding it through the glass. It burns off with the sun. Nothing to fix.
Haze between the panes that cannot be wiped at all means the perimeter seal on the insulated glass unit has failed. That seal holds an inert gas fill between the panes and keeps outside air out. Once it breaks, humid air cycles in and out with every temperature swing and condenses in a space nobody can reach. After a while you get a permanent white mineral film, left behind as that moisture evaporates and returns.
Why seals fail, and why they fail in batches
An insulated glass unit expands and contracts every day as the sun hits it and then leaves. The sealant at the perimeter absorbs that movement, and it does so for a long time before it hardens and cracks. South and west-facing windows take the most thermal cycling and fail first, which is why failures tend to march around a house in a predictable order.
The part that surprises people is the timing. Because a whole house of windows usually went in on the same day, they age on the same clock. When the third window in two years goes hazy, the rest are not far behind.
That pattern is especially visible in the 1990s and 2000s subdivisions across Salmon Creek and Orchards, where entire streets were built inside a short window and are now reaching the same milestone together. If your neighbors are replacing glass, that is a useful signal about your own.
Across the river the cohort effect is even sharper. Gresham grew from under 4,000 residents in 1960 to over 65,000 by 1990, so window replacement in Gresham tends to arrive as a whole-house conversation rather than a single bad unit. Worth knowing there is a second, unrelated problem on the older stock: single-pane aluminum frames conduct cold well enough to condense on the frame itself, and no glass upgrade fixes a frame.
On window defogging services
You will find companies that drill a small hole in the glass, dry the cavity and install a breather valve. The haze clears, and it costs less than replacement, so it is a reasonable stopgap if you are selling soon.
Understand what it does and does not do. It clears the view. It does not restore the seal, and it does not bring back the gas fill or the insulating performance, because the unit is now vented to outside air by design. You have converted a failed insulated window into a clear-looking single-performance one. For a house you plan to keep, replacing the glass or the window is the fix that lasts.
Getting the condensation under control
If your fog wipes off, the underlying issue is that a Pacific Northwest house spends five months closed up while generating a lot of moisture. Four things move the needle.
Run the bath fan longer than feels necessary. Twenty minutes after the shower ends, not two. A timer switch solves it permanently. One shower puts more water into the air than a day of cooking.
Cover the crawl space. An unvented or poorly covered crawl space pushes ground moisture straight up into the living space all winter. A proper vapor barrier is one of the highest-return moisture fixes in this climate and most homeowners never think about it.
Use the range hood, and confirm it vents outside. A recirculating hood filters grease and hands every bit of the steam back to the room.
Check the attic ventilation. Moisture that cannot escape the attic keeps the whole envelope damp. Under-ventilated attics show up as window condensation, ceiling stains and shortened roof life at the same time, which is why balanced roof and attic ventilation matters well beyond the roof.
Replacing a failed window: insert or full-frame
Once you are replacing, there is one real decision, and it is not the brand.
An insert replacement sets a new window into the existing frame. It is faster, it leaves your interior trim alone, and it requires that the existing frame and the rough opening behind it are dry and structurally sound.
A full-frame replacement takes the old window out down to the framing. It takes longer, and it is the only correct answer when there is rot in the sill or the sheathing around the opening.
That distinction carries more weight here than in a dry climate. Windows installed before modern flashing practice often have no sill pan at all, and with this much annual rain, water that gets past the trim has been soaking framing for years. We open a corner and check before recommending either approach, because quoting an insert on an opening with a rotted sill is how a job doubles in scope mid-week. If you are weighing frame materials as well, our comparison of vinyl and fiberglass window frames covers how each holds up here.
The one time to do windows early
If the wall is coming off for new siding, that is the moment to do full-frame windows even if the glass has a few years left. The sheathing is exposed, the pan flashing gets done properly, and the two trades stop working around each other. Doing it in the other order means cutting into brand new siding later.
Get the opening looked at before you buy glass
The window is the easy part. What sits behind it decides the scope. We check the rough opening for rot before quoting window replacement and installation, so the number you get is the number you pay.