Window condensation: glass, panes, or frames
"The windows are sweating" is the most common moisture report a Vancouver property manager receives, and it describes three different findings. Water on the room-side glass, fog trapped between the panes, and drips running off the frames have three different causes, three different owners, and three very different price tags. This guide separates them.
Three findings that only look alike
A window is a diagnostic instrument if you read it in the right order: glass first, the space between the panes second, frame and sill last. Each location tells its own story.
| What you find | What it means | What to do about it |
|---|---|---|
| Water on the room-side glass | The room air is humid and the glass is the coldest surface it can reach. The window is acting as a gauge, reporting on the suite. Common on cold mornings, worst in bedrooms and kitchens. | Mostly a ventilation and habits problem. Wipe the sills so finishes survive, then reduce the moisture load and improve air movement. Persistent pooling that soaks sills and drywall deserves a closer look. |
| Fog or haze trapped between the panes | The sealed unit has failed. Double glazing works because the space between panes stays dry; once the perimeter seal lets moist air in, condensation forms where no cloth can reach it. The unit has also lost part of its insulating value. | A glazing repair, and a planning question rather than an emergency. One fogged unit is a suite matter. Many fogged units on the same elevation belong on the strata renewal plan. |
| Water beading on frames and dripping onto sills | Thermal bridging in miniature. Older aluminum frames conduct heat straight through to the outside, so the metal runs close to outdoor temperature and condenses room moisture even when the glass stays fairly dry. | Habits help but rarely solve it, because the frame will always be the coldest thing in the room. Frame condensation on every cold day is an argument for window renewal, weighed at the building level. |
Water on the glass: the room talking
Surface condensation on the inner glass is the suite reporting its own humidity. The moisture comes from showers, cooking, drying laundry, and the occupants themselves, and the glass is simply the coldest surface on offer. A light morning haze along the bottom edge during a cold snap is life in an occupied suite. Glass that streams, pools on the sill, and soaks the curtains is a moisture load running ahead of the ventilation, and the fixes live in the ventilation and exhaust guide and the winter habits covered elsewhere in the condensation and moisture hub.
One warning before anyone relaxes about "cosmetic" glass condensation: the water still has to go somewhere. Sills, paint, and the drywall below the window take the damage a wipe-down would have prevented. And damp that never dries invites staining on the wall below, at which point it starts to imitate a leak.
Fog between the panes: a failed sealed unit
A modern window is really two products: the frame, and the insulated glass unit sitting in it. The unit is a factory-sealed sandwich, two or three panes around a dry cavity. Its whole performance depends on that cavity staying sealed. When the perimeter seal fails, and every seal ages toward failure, moist air breathes in and out of the cavity with the weather. The first symptom is a haze that appears on cool mornings and vanishes by afternoon, which owners dismiss for a year or two. Eventually mineral deposits etch the inner surfaces and the fog becomes a permanent grey bloom no cleaner can touch.
A fogged unit is a performance and visibility failure, with the wall around it typically staying dry, and it can be replaced on its own: glass sandwich out, new sandwich in, frame untouched. The strata-level question is population math: sealed units installed together age together, so the first few fogged units on an elevation are usually the leading edge of a wave. Counting fogged units building-wide, the way a depreciation report counts components, turns a trickle of suite complaints into a plannable renewal scope.
Drips off the frame: thermal bridging in miniature
Older aluminum frames, common in Metro Vancouver towers glazed before thermally broken extrusions became standard, conduct heat the way metal does: enthusiastically. The room-side face of the frame runs close to outdoor temperature, which makes it the coldest object in the suite, colder than the glass it holds. Moisture beads on the metal, runs down, and collects on the sill morning after morning. Residents wipe the glass and wonder why the sill is still wet.
This is the same physics covered in the thermal bridging guide, shrunk to window scale. Habits reduce how much moisture is available to condense, but they cannot warm the metal. Where frame condensation is chronic across a building, the honest answer is window renewal with thermally broken frames, sequenced through the strata's capital planning rather than sold as an emergency.
When the window is blamed for the wall
Windows collect accusations because they are where water shows first. But staining beside or below a window, damp on the window returns, or a report that tracks storms rather than cold mornings points away from condensation and toward the perimeter: sealant joints, flashings, and the wall assembly itself. Perimeter sealant on Vancouver towers has a finite service life, a failure mode we cover in our article on window sealant failure on curtain wall towers, and the reads that separate storm water from room moisture are the whole subject of the condensation versus leak guide.
Where the perimeter is the suspect, the fix is envelope work: joint replacement through a sealant and caulking program, or investigation and repair through our building envelope repair service. Rope access makes window perimeters cheap to inspect on a tower, which is why we test before anyone replaces glazing that was never the problem.
Quick answers
Why does condensation form on the inside of my windows in winter?
Glass is usually the coldest surface a suite offers, so the moisture in the room air condenses there first. Cooking, showers, laundry, and breathing all load the air, and on a cold Vancouver morning the inner face of the glass sits below the dew point of that air. The window is acting as a moisture gauge for the suite: heavy condensation means the room is carrying more water vapour than its ventilation is removing.
What does fog between the panes of a double-glazed window mean?
Fog trapped between the panes means the sealed unit has failed. A double-glazed unit is a factory-sealed sandwich with dry air or gas between the panes, and its perimeter seal is what keeps that space dry. Once the seal fails, humid air cycles in and out and condenses on the inner surfaces where nobody can wipe it. The haze often comes and goes with the weather at first, then becomes permanent staining.
Can a fogged sealed unit be repaired, or does the glass need replacing?
The standard fix is replacing the sealed unit itself, the glass sandwich, while keeping the existing frame. That is a much smaller job than replacing the whole window. Whether it is worth doing one unit at a time depends on the building: if units are fogging across an elevation, the seals are aging as a population, and a strata is usually better served pricing a phased renewal than replacing units one by one as they fail.
Window condensation questions
Why does condensation form on the inside of my windows in winter?
Glass is usually the coldest surface a suite offers, so the moisture in the room air condenses there first. Cooking, showers, laundry, and breathing all load the air, and on a cold Vancouver morning the inner face of the glass sits below the dew point of that air. The window is acting as a moisture gauge for the suite: heavy condensation means the room is carrying more water vapour than its ventilation is removing.
What does fog between the panes of a double-glazed window mean?
Fog trapped between the panes means the sealed unit has failed. A double-glazed unit is a factory-sealed sandwich with dry air or gas between the panes, and its perimeter seal is what keeps that space dry. Once the seal fails, humid air cycles in and out and condenses on the inner surfaces where nobody can wipe it. The haze often comes and goes with the weather at first, then becomes permanent staining.
Can a fogged sealed unit be repaired, or does the glass need replacing?
The standard fix is replacing the sealed unit itself, the glass sandwich, while keeping the existing frame. That is a much smaller job than replacing the whole window. Whether it is worth doing one unit at a time depends on the building: if units are fogging across an elevation, the seals are aging as a population, and a strata is usually better served pricing a phased renewal than replacing units one by one as they fail.
Why do aluminum window frames drip water in cold weather?
Plain aluminum conducts heat extremely well, so an older frame without a thermal break carries outdoor cold straight through to its room-side face. On a cold morning the metal can sit far below the temperature of the surrounding wall, which makes it the first surface in the suite to fall below the dew point. Moisture beads on the frame, runs down, and pools on the sill, even in suites with reasonable humidity habits.
Is window condensation the fault of the window or of the suite?
It depends on where the water sits. Fog between the panes is the window, full stop. Water on the room-side glass is mostly the suite: its moisture load and ventilation. Frame condensation sits in between, because habits set how much moisture is available but the frame design sets how cold the landing surface gets. Reading the three locations separately is what keeps stratas from buying the wrong fix.
Does replacing windows stop condensation for good?
It removes the coldest surfaces, which helps a great deal, and modern thermally broken frames with better glazing condense far less. But the moisture in the air does not vanish; it goes looking for the next coldest spot. Suites that replace windows without touching ventilation sometimes trade wet glass for damp closet corners. Window renewal works best paired with working exhaust fans and sensible winter habits.
Why is window condensation worse on north-facing windows?
North elevations in Metro Vancouver get little direct sun through the winter, so their glass and frames never receive the daily warm-up that dries south-facing windows by mid-morning. The surfaces run colder for more hours per day, which means more hours below the dew point of the suite air. The same suite humidity that leaves a south window dry by breakfast can keep a north window wet until noon.
Why do new windows sometimes condense more than the old ones did?
Because old windows leaked air. A draughty single-glazed window ventilated the suite by accident, carrying moist air out through its gaps all winter. Replace it with a tight modern unit and that accidental ventilation disappears, so suite humidity climbs and condensation can appear on surfaces that were dry before. The new window did its job; the suite now needs its ventilation to do the job the draughts were doing.
Is condensation on the outside of windows a problem?
No. Exterior condensation on high-performing glazing happens on clear, still mornings when the outer pane radiates heat to the sky and drops below the outdoor dew point, exactly like dew on a car. It is a sign the glazing is insulating well, since so little indoor heat reaches the outer pane. It clears as the morning warms and needs no action at all.
In a strata building, who is responsible for window condensation problems?
It turns on what the windows are in that strata's bylaws. In many BC stratas, windows and their sealed units are common property, which puts fogged units and failing frames on the corporation, while suite humidity and ventilation habits sit with the owner. Councils should check their own bylaws and the Strata Property Act framework before promising either answer, because the split varies between corporations.
When does window condensation justify an envelope assessment?
When the evidence stops being cosmetic: water staining the wall below or beside the window, soft drywall at the sill line, paint lifting on window returns, or damp that persists in mild weather. Those signs raise the possibility that the perimeter sealant or flashing is admitting water alongside the condensation, and the two problems share a postcode. An assessment separates them with surface readings and, where needed, water testing.
Wet windows every morning?
We assess windows, perimeter sealants, and the walls around them on strata and commercial buildings across Vancouver, Burnaby, and the North Shore, and we tell you which of the three findings you actually have.