The signs you need new windows are condensation trapped between the panes, glass that stays hot to the touch through the afternoon, sashes that stick or will not lock, visible damage to the frame, and water staining on the trim or wall below. In Southern California, one more sign matters more than any of those: single-pane aluminum windows, which most homes in the region were built with and which have now outlived the material’s expected service life.
Most advice on this subject is written for cold climates and wood windows. It tells you to feel for cold air in winter and to look for soft, rotting frames. That is the wrong test in a place where the cooling season runs most of the year and the frames are metal.
The problem here is heat coming in, not warmth leaking out
In a heating climate, a bad window loses conditioned air to the outside and you feel it as a draft. In a cooling climate, the dominant load runs the other way: solar energy passes through the glass and becomes heat inside the room, and the air conditioning spends the afternoon removing it.
That changes what you should be checking. Stand next to a west-facing window at four in the afternoon and put a hand near the glass without touching it. Radiant heat you can feel from a few inches away is solar gain arriving through the glazing, and no amount of caulk or weatherstripping will change it. What changes it is the glass itself: a second pane, an insulating gas fill, and a low-emissivity coating that reflects the infrared part of sunlight while letting visible light through.
Draft sealing still matters, and the standard test still works. Close and lock the window, then hold a hand near the frame edges and corners and feel for moving air. But on most homes in this region, sealing the perimeter of a single-pane window addresses the smaller half of the problem.
Aluminum is the regional story and nobody tells it
A large share of Southern California housing was built between the 1950s and the 1980s with single-pane aluminum windows. Aluminum framing conducts heat readily, so the frame itself becomes a thermal bridge: the metal warms in the sun and carries that heat into the room independently of the glass.
Aluminum also carries the shortest expected service life of the common window materials, shorter than vinyl, maintained wood or fiberglass. Windows installed in this region in the 1960s and 1970s are well beyond it.
Aluminum does not fail the way wood does. It will not go soft or spongy, so the rot test that dominates the advice online returns nothing useful. It fails by binding as the frame distorts, by corroding and pitting at the corners and sill, by losing the glazing seal that holds the pane, and by condensing water on the interior face of the frame on cool mornings because the metal is colder than the room air.
Condensation, and the one distinction that matters
This is the most commonly confused signal on the whole subject, and the distinction is simple.
Condensation on the inside surface of the glass, or on the outside surface, is about humidity and temperature. It is usually normal, and exterior condensation on a cool morning is generally a sign the glazing is working, because the outer pane is staying close to outdoor temperature rather than being warmed from inside.
Condensation trapped between the panes is different and it is definitive. It means the seal around the insulated glass unit has failed and moisture has entered the cavity. That seal cannot be effectively repaired once broken, so the affected unit needs replacing. Persistent haze or mineral-looking spotting between the panes is the same failure at a later stage.
Water where it should not be
Water entering around a window is a failure of the installation and flashing rather than the window, and it is the sign most worth acting on quickly because the damage compounds behind the finish. Look for water staining on the trim or the drywall beside or below the opening, paint bubbling around the frame, flooring that has cupped or warped directly under the window, a persistent mildew smell near the opening, or caulk lines that have split and pulled away.
On a stucco house this matters more than it sounds. The water path runs behind the stucco, so by the time it shows on the interior it has usually been running for a while, and the repair scope may extend past the window itself.
What can be repaired, and what cannot
Not every symptom means replacement, and a contractor who says otherwise is worth a second opinion.
Genuinely repairable: worn weatherstripping, sticking or broken latch and crank hardware, a torn screen, minor cosmetic damage to the frame, and a single cracked pane in an otherwise sound window.
Generally not repairable: a failed seal between the panes, frame distortion or corrosion that prevents the sash from closing and locking, water entry around the opening, and the underlying performance of single-pane glass, which is a property of the unit rather than a defect in it. When the same window keeps needing attention, or when repair quotes start approaching the cost of a new unit, the arithmetic has already changed.
The two questions that come next in California
Once replacement is on the table, two things come up here that the general advice never mentions.
The first is installation method. Retrofit installation, sometimes called pocket or insert installation, fits a new unit inside the existing frame without disturbing the surrounding stucco. Full-frame replacement removes the whole assembly down to the rough framing, which is necessary where there is water damage, rot in the framing, or a change in opening size. Most intact stucco homes are retrofit candidates, and that single determination drives the scope more than the product choice does.
The second is that replacing windows in California is permitted work, so the state energy code applies and the products have to meet the performance required for your climate zone. This is not a formality bolted on at the end; it constrains which units are eligible before you choose one. Dual pane units with low-emissivity coatings are the normal answer, and a whole-house window replacement is usually planned around compliance and access rather than around the shopping list. The current standards, and the climate zone map that decides which apply to your address, are published by the California Energy Commission.
Frequently asked questions
What is the average lifespan of a home window?
Lifespan depends on the frame material more than on the glass, and aluminum has the shortest expected service life of the common materials, with vinyl, maintained wood and fiberglass all lasting longer. Age alone is not the deciding factor. Multiple symptoms appearing together, such as a failed seal plus binding sashes plus water staining, is a stronger signal than a date.
Should 20 year old windows be replaced?
Not automatically. A 20 year old dual-pane vinyl or fiberglass window in good condition with an intact seal has service life remaining. A 20 year old window showing fogging between the panes, binding operation or water entry is a different case. In Southern California the more useful question is usually not the age but whether the window is single-pane aluminum, because that combination is typically much older than 20 years and underperforms regardless of condition.
Which month is best to replace windows?
In most of the country the answer is driven by weather, since openings are exposed during the work and installers avoid the coldest and wettest months. Southern California removes most of that constraint, which means scheduling is driven by installer availability and lead times on the units rather than by season. The practical planning point is the gap between ordering and installation, because units are made to the measured opening.
Is it cheaper to replace all windows at once?
Doing the house in one project usually costs less per window than doing it in stages, because mobilization, measurement, permitting and installation crew time are spread across more units. Replacing a single window makes sense when that window has a specific problem such as broken glass. Where the goal is comfort, noise or energy performance across the house, staging the work spreads the same total across more visits rather than reducing it.
Can a foggy window be repaired?
No, not in any lasting way. Fog between the panes means the seal around the insulated glass unit has failed and moisture has entered the sealed cavity. That seal cannot be effectively restored once broken. Depending on the window, the insulated glass unit alone can sometimes be replaced within the existing frame rather than replacing the whole window, which is worth asking about when the frame is otherwise sound.
Do I need a permit to replace windows in California?
Replacing windows generally requires a building permit, and permitted work brings the state energy code with it, so replacement units have to meet the performance required for the climate zone. Changing the size of an opening adds structural review because the framing changes. Your contractor normally handles the application and the inspection, and the signed-off permit is what records that the work was checked.
