You clean the window. The haze is still there. You clean it again from the outside, and it is still there, because it is not on the glass at all. It is between the two panes, and no amount of Windex is ever going to reach it.
That milky film means the sealed unit has failed. It is the single most common call we take in Sacramento, and the good news is that fixing it is usually cheaper and less disruptive than people expect.
What a dual-pane window actually is
A double-pane window is not just two pieces of glass. It is a manufactured assembly, two panes bonded to a spacer around the edge, with a sealed airspace between them, often filled with argon. That spacer is packed with desiccant, a drying agent whose whole job is to absorb the small amount of moisture trapped inside when the unit was built.
The assembly is called an insulated glass unit, or IGU. It sits inside your window frame. The frame, the sash, the hardware and the trim are all separate from it.
Why the seal gives out, and why Sacramento is hard on them
Sunlight heats the sealed airspace and the gas inside expands, pressurizing the unit. At night everything cools and contracts. Do that every day for years and the perimeter seal works like the bellows of a forge, flexing thousands of times until small fractures open up.
Sacramento gives that cycle about as much to work with as any climate in California. We get roughly ninety days a year above 90°F and around two dozen above 100°F. Then, most summer evenings, the Delta breeze pushes marine air through the Carquinez Strait and the temperature can fall twenty or thirty degrees in a few hours. Big swing up, big swing down, every single day of the season. Add high clear-sky UV working on the sealant itself and you have a window assembly being asked to breathe harder than it was designed to.
Once the desiccant is saturated, it cannot absorb any more moisture, so humid air that gets pulled in overnight condenses on the inside of the glass. That is the fog.
Why the same windows always go first
Look at which windows fogged and you can usually guess the exposure. West and south-facing glass takes the longest, hottest load and fails earliest. Large fixed picture windows go before small ones because there is more sealed perimeter and more gas volume moving. And if a whole house fogged over within a couple of years, it is almost always because every unit was installed at the same time and has been cycling together ever since.
Around here, the first generation of retrofit dual-pane windows, the ones dropped into Sacramento houses through the late 1980s and 1990s, is reaching the end of its service life all at once.
What does not fix it
You will find services that drill a small hole in the glass, dry the unit out and fit a vent. The haze goes away for a while. What it does not do is restore the seal or replace the desiccant, so the unit is still breathing outside air, the insulating gas is gone, and the moisture tends to come back. We do not sell it, because we would only end up replacing the unit later anyway.
Cleaning does nothing. Running a dehumidifier in the room does nothing. The moisture is sealed inside a manufactured assembly.
What the actual repair looks like
We replace the insulated glass unit and leave everything else alone:
- We measure the existing unit, glass size, overall thickness, spacer depth, and whether it needs to be tempered, Low-E or obscure
- A new unit is built to those measurements
- We take out the failed unit, set the new one and re-seal it in the same frame
Your frame stays. Your trim, stucco, siding and interior casing stay. The paint line does not get touched. In most cases it is a single visit, and you get a window that looks the way it did the year it went in.
What drives the price
Glass is priced by what it has to do, not just by size. The things that move the number are the size of the opening, whether the location requires tempered safety glass, whether you want Low-E coating to cut heat gain, whether the glass is obscure or patterned, and how difficult the window is to reach, a ground-floor bedroom and a second-story unit over a landscaped bed are not the same job.
That is why we measure on site and put the figure in writing before anything is ordered. Glass is cut to your opening, so there is no restocking a wrong guess.
One thing worth checking first
If the condensation wipes away, it is on the room side of the glass and the seal is fine, that is humidity in the house meeting cold glass, and it points at ventilation rather than the window. If it does not wipe away from either side, the unit has failed.
Not sure which one you have? Send us a photo. We can usually tell from the picture, and if it is the simple answer we will tell you that too.