Windows & Doors Warning Signs: A San Francisco Homeowner's Reference Guide

Windows & Doors Warning Signs: A San Francisco Homeowner’s Reference Guide

A double-pane window with a broken seal loses 30 to 50 percent of its insulating value the day the seal fails, and because the fogging only shows up on cold mornings, most San Francisco homeowners underestimate how long the unit has been quietly underperforming. This guide names the specific symptoms, explains the failure mechanism behind each one, and tells you which problems are a five-year concern and which are a five-month concern. You’ll learn how to read what your windows and doors are telling you, where to look first, and when the right move is repair, replacement, or a call to a professional who will put the price in writing before any work starts. For a deeper dive, see our Complete Guide to Windows & Doors in San Francisco.

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Quick Answer

The most common warning signs that San Francisco homeowners should watch for are condensation between double-pane glass (a failed seal), drafts that move a tissue near closed windows or doors, wood rot that softens under a screwdriver probe, doors that no longer sit square in their frames, and sashes that stick or refuse to stay open. A failed insulating glass unit typically costs $350 to $700 per sash to replace in San Francisco, while a full window replacement runs $800 to $1,800 per opening depending on the manufacturer line and installation complexity. If you can see daylight around a closed door, feel a temperature difference within three feet of a window, or press a probe a quarter-inch into a sill, those are five-month problems, not five-year problems. Not sure whether to tackle it yourself or call a pro? Read our DIY vs Professional Windows & Doors: The San Francisco Homeowner’s Decision Guide.

Table of Contents

• Condensation: Surface Moisture vs. Failed Seal
• Draft Detection Without Equipment: The Hand-Test and the Tissue-Test
• Wood Rot in San Francisco’s Climate: The Three Stages and When Replacement Beats Repair
• Door Misalignment: Hinge Problem or Foundation Signal?
• Five Warning Signs That Void Most Window Warranties
• Sash Mechanics: Sticking, Dropping, and What They Tell You
• Hardware and Weatherstripping: The Inexpensive Failures That Cost the Most
• What San Francisco’s Marine Layer, Fog, and Victorian Housing Stock Mean for Your Windows
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions

Condensation: Surface Moisture vs. Failed Seal

Condensation on the room-side surface of a window is normal in San Francisco, especially during the summer months when the marine layer keeps outdoor humidity high. Condensation between the two panes of a double-pane window is never normal. It means the insulating glass unit, known in the trade as an IG unit, has lost its seal and the desiccant inside the spacer bar has become saturated. Once that happens, the argon or krypton gas that provided much of the unit’s thermal performance has escaped, and the window is now performing at roughly half its original insulating value.

The diagnostic difference is simple. Surface condensation wipes away with a cloth. Between-pane condensation does not, because the moisture is trapped inside the sealed airspace. In a photograph, surface condensation appears as a uniform haze or droplets on the glass. Failed-seal condensation typically appears as a milky film or water droplets that sit behind the outer glass, sometimes in a crescent shape along the bottom of the unit. On a cold San Francisco morning in neighborhoods like the Sunset, Richmond, or Twin Peaks, where overnight temperatures dip and fog rolls in, a failed seal will show itself as a persistent interior fog that does not respond to wiping.

Here is the threshold that matters. If the between-pane fog appears only occasionally, on cold mornings after a warm day, the seal has failed but the unit still has some residual gas. You have months, not years. If the fog is present most mornings and the glass has a permanent milky or streaked appearance, the desiccant is saturated and the unit is done. In our experience, the second condition is common on the west-facing windows of San Francisco homes that get full afternoon sun followed by fog-chilled nights. That thermal cycling is exactly what stresses edge seals on aging units.

The replacement math is straightforward. Replacing a failed IG unit within an existing frame typically runs $350 to $700 per sash in San Francisco. Replacing the entire window, frame and all, runs $800 to $1,800 per opening depending on the manufacturer line and whether the opening requires custom sizing. For a more detailed look at full window replacement in San Francisco, including what the process looks like from measure to final inspection, see our guide on Window Replacement in San Francisco.

If the window is under warranty, this is the moment to read the fine print before you call anyone. Most manufacturer warranties cover the IG unit but pro-rate the coverage over time, and most exclude seal failure caused by improper installation, which is why the five warning signs we cover later in this guide matter. A failed seal on a window that was installed out of square will often be denied, and the denial will cite the installation angle. That is why the written guarantee on installation matters as much as the warranty on the glass.

Draft Detection Without Equipment: The Hand-Test and the Tissue-Test

Drafts are the most commonly misdiagnosed window and door problem in San Francisco, because the city’s microclimates produce genuine temperature differences from room to room even when every seal is intact. A cool pocket near a window is not proof of a draft. But there are two tests that will tell you more in thirty seconds than a thermal camera rental. Both are free and both require nothing but your hands and a piece of tissue paper.

The hand-test works like this: stand near the closed window or door on a cool morning, close your eyes, and move your open palm slowly along the perimeter of the sash, the meeting rail where the sashes overlap, and the junction between the frame and the wall. Do not press your hand against the surface. Hold it an inch away. A functioning window will feel uniformly neutral. A draft will register as a localized cold stream moving across your palm. The location of that cold stream tells you the failure point. Air moving along the top of the sash suggests a broken or compressed head weatherstrip. Air at the meeting rail means the sash lock is not drawing the two sashes together tightly enough, or the interlock weatherstrip has degraded. Air at the frame-to-wall junction means the rough opening was never properly insulated, which is a common finding in San Francisco homes built before modern insulation standards.

The tissue-test is more precise. Tear off a single sheet of tissue paper, hold it near the window or door seam at the suspected location, and watch what it does. A tissue that hangs still means no measurable air movement. A tissue that flutters, waves, or is pushed away from the seam means air is moving through at that exact point. Run the tissue-test along every seam: top, bottom, both sides, and the meeting rail. The test will also reveal drafts that the hand-test misses when the temperature difference between inside and outside air is small.

Neither test requires tools, but both require patience. Move slowly. A draft that only appears when the wind gusts from a particular direction is still a real draft, and it is often the one that matters most on San Francisco’s windward-facing hillsides. Homes in the Outer Sunset, Noe Valley wind corridors, and the higher reaches of Diamond Heights get pushed by steady onshore flow that a protected inner-block home never feels. If the tissue flutters only when the wind picks up, the failure is real, and it will get worse as the weatherstrip continues to compress.

Wood Rot in San Francisco’s Climate: The Three Stages and When Replacement Beats Repair

San Francisco’s fog, salt air, and winter rain cycles create a specific rot pattern: slow to start, fast to finish. A wood sill can look perfectly sound for a decade, then cross from surface graying to structural softening in a single wet winter. The city’s older housing stock, particularly Victorians and Edwardians with original wood windows, is the most vulnerable, because those units were built long before modern joinery and protective coatings existed. Here is how rot progresses in this climate, and how to tell which stage you are looking at.

Stage 1: Surface graying and paint lifting. The first sign is usually paint that starts to lift at the bottom corner of the sash or the sill nose. The wood underneath will be gray or silvered but still hard. A screwdriver pressed into the wood meets resistance and does not leave a lasting dent. This is the repair stage, and in most cases, it means scraping the failed paint, treating the wood with a borate preservative, and repainting. The window itself is still sound. Budget $150 to $400 for a professional repair of this type on a single window in San Francisco, depending on access and whether the surrounding trim also needs work.

Stage 2: Soft probe response. Press the screwdriver into the same area. If the tip sinks a quarter-inch or more with moderate pressure, or if small chunks of wood flake away when you scrape, the rot has passed the cosmetic stage. The structural wood is compromised, but it may still be repairable with epoxy consolidation or a dutchman splice, depending on how far the damage extends. This is where an honest assessment matters: a dutchman repair on a single sill section runs $300 to $600, and if the rot wraps around the corner into the jamb, replacement becomes the better investment. The threshold most contractors use is simple: if the rot affects more than 20 percent of the sill’s total length, or if any part of the rot reaches the weight pocket, replace the sill. Patching beyond that point is gambling.

Stage 3: Structural softening and visible gap. If the screwdriver sinks more than half an inch with light pressure, or if you can see a visible gap where the sill meets the jamb, the wood is no longer load-bearing. This is a replacement situation, and it is not optional. In Victorian-era San Francisco homes, this stage is often accompanied by the subtle outward tilt of the lower sash, because the sill that supported it has lost its bearing surface. A full sill replacement, including interior and exterior trim, runs $600 to $1,500 per window in San Francisco, and the number goes up when access requires ladders on a hillside home or scaffolding on a third-story bay window. Delaying at this stage invites water intrusion into the wall cavity, which is a far more expensive problem than any window.

The single best preventive move in this climate is to keep paint intact and to re-caulk the exterior perimeter every three to five years. Silicone or polyurethane caulk outperform acrylic latex in San Francisco’s marine air, and the difference in lifespan is roughly double. It is also worth checking the angle of the exterior sill: a sill with a proper drip edge sheds water away from the wall. A flat sill holds water against the wood and speeds the rot cycle.

Door Misalignment: Hinge Problem or Foundation Signal?

A door that no longer closes square is sometimes a hinge problem and sometimes a structural problem, and the difference is determinable in under a minute. The test is visual: stand at the hinge side of the open door and look at the reveal, the gap between the door slab and the jamb. A door with worn hinges will typically sag, meaning the reveal narrows at the top latch-side corner and widens at the bottom latch-side corner. The tell is consistent. The top of the door rubs against the jamb, the bottom corners drag on the threshold, and the fix is either tightening the hinge screws or replacing the hinges. That is a $50 to $200 repair, and no foundation is involved.

A door that is out of plumb but has a uniform reveal around all three sides is a different signal. The door slab has not moved. The frame has moved, and in most cases, that means the rough opening has moved with it. In San Francisco, where hillside homes, landfill-adjacent neighborhoods like the Marina and the Bayview, and century-old brick foundations are common, frame movement is frequently a settling symptom rather than a hinge symptom. The specific warning sign is a door that opens or closes on its own, or one that sticks at the top and bottom simultaneously while the reveals stay even. That is not hinge wear. That is racking.

The practical takeaway is this: if the reveal is even and the door is rubber, pull a level across the jamb. A jamb that is off plumb by more than a quarter-inch over the height of the door should be checked by a professional who understands structural movement. This does not automatically mean a failing foundation. San Francisco houses on hillsides accept a certain amount of seasonal movement as the soil expands and contracts through wet and dry months. But the pattern matters. A door that gets progressively harder to latch over a six-month period, or one that shifts seasonally and never returns to its original position, is a five-month problem. Get it evaluated.

For doors beyond the racking question, the bigger concern is whether the door is worth re-hanging at all. An exterior door that has reached the point of repeated hinge failure is often better replaced than repaired, especially if it is an older wood slab with single-pane glazing. Modern patio door systems from manufacturers like Therma-Tru and ES Windows are engineered with reinforced frames and multi-point locking that hold alignment far better than a 40-year-old slab in a shifting rough opening. If you are considering a new door, see our page on Patio Door Installation in San Francisco for what a written, fixed-price install looks like from measurement to final adjustment.

Five Warning Signs That Void Most Window Warranties

Most window manufacturers write their warranties with specific exclusions, and the five most common ones are all conditions a homeowner can spot before filing a claim. What follows is the list, in plain terms, because you should know where you stand before you call a manufacturer or a contractor. None of these are exotic. Most are things a homeowner sees every day and dismisses as normal.

1. Water staining on the interior sill or the drywall below the window. This tells the manufacturer that water has been entering the opening, and the first question the claims adjuster asks is whether the window was properly flashed and sealed at installation. If the answer is unverifiable, the claim gets denied on the installation exclusion.
2. Windows that are visibly out of square. A sash that sits crookedly in the frame stresses the glass and the seals. Manufacturers exclude damage caused by structural movement or improper installation. The crooked sash is the evidence of that exact condition.
3. Failed exterior caulk or missing backer rod around the frame. This is the maintenance exclusion. Once the perimeter seal fails, water gets behind the frame, and the resulting damage is classified as neglect, not a manufacturing defect.
4. Condensation between the panes that appears more than one year after a known impact. Hairline cracks from a stray baseball or a wind-thrown branch are excluded if the impact can be documented. The failed seal shows up months later. The manufacturer ties the two together and voids the claim.
5. Repairs performed by anyone other than the manufacturer’s authorized channel. Not every manufacturer enforces this, but most reserve the right to deny a claim if the work was done by someone who was not qualified to touch the product. This is why the warranty on the installation itself matters as much as the warranty on the glass.

The takeaway is simple. If you see water staining, crooked sashes, failing caulk, or impact marks, address them before filing a claim. Document everything with photographs. And when you do replace windows, ask the contractor to put the installation warranty in writing. A written guarantee on the work, like the 365-Day Done Right Promise our crews work under, is the thing that protects you when the manufacturer points to the installation as the cause of a failure.

Sash Mechanics: Sticking, Dropping, and What They Tell You

A window sash that sticks in humid weather and frees up in dry weather is usually a swelling problem, not a mechanical problem. Wood absorbs moisture from San Francisco’s marine air, expands slightly, and binds in the frame. The question is whether the binding is seasonal or progressive. Seasonal binding comes and goes. Progressive binding gets worse every month, because the underlying cause, a failing balance system in a double-hung window or a worn roller in a slider, is not reversible with weather.

Here are the specific symptoms and what they mean.

• A double-hung sash that drops when you release it. The balance system, either a spiral balance or a block-and-tackle balance, has lost tension. This is a mechanical failure, and it will not self-correct. The repair is a balance replacement, typically $100 to $250 per sash in San Francisco.
• A sash that sticks only at one corner. The corner joint has loosened, or the jamb has shifted slightly. If the reveal is uneven, the jamb is the culprit. If the reveal is even, the sash itself is racked.
• A sliding window or patio door that drags and then stops. The rollers have worn flat, or the track is packed with dirt and debris. A track cleaning is the first move. If the drag persists, the rollers need replacement. In a San Francisco home with salt air exposure, roller corrosion accelerates, and replacement is usually the answer.
• A sash that will not lock without excessive force. The keeper and lock have moved out of alignment, usually because the sash has dropped. Forcing the lock repeatedly will eventually break the mechanism or fracture the sash corner.

The order of operations matters. Diagnose before you repair. Clean the track or check the balance tension before replacing parts. And if the diagnosis is unclear, do not start pulling the window apart. Misdiagnosis on a mechanical repair usually costs more than the repair would have, which is exactly the kind of waste that written pricing and a disciplined process are designed to prevent. Our page on Window Installation in San Francisco walks through the full assessment process, including the specific measurements that determine whether a repair or a replacement is the right investment.

Hardware and Weatherstripping: The Inexpensive Failures That Cost the Most

The cheapest components in a window or door are the hardware and weatherstripping, and they are also the components whose failure causes the most expensive secondary damage. A failed weatherstrip on an exterior door lets in a draft, which is a comfort problem. But it also lets in moisture, which is a rot problem. The weatherstrip that costs $15 to replace becomes a $600 door frame repair if the water gets behind the jamb. The economics are not subtle.

Weatherstripping on windows and doors should be inspected visually once a year. What you are looking for is compression set, where the foam or pile has flattened and no longer springs back, and breakage, where the strip has torn or pulled away from its groove. In San Francisco, where windows get opened and closed constantly through the shoulder seasons, weatherstripping wears out faster than it does in climate-controlled climates.

Hardware failures are similar. A lock that requires force is not getting stronger with use. A hinge that squeaks and binds is not settling in. A handle that wobbles is not tightening itself. Each of these is a mechanical signal that the component has reached the end of its service life, and each one is cheap to fix now and expensive to fix later. The screw holes that wallow out in a wood door frame, for example, are the result of repeated lateral force from a sagging hinge. Re-drilling and re-setting the hinge is a 20-minute job. Replacing the jamb because the wood has split is a half-day job.

Manufacturers like Mr-Glass and ECO Window Systems have made significant improvements in factory-installed weatherstripping over the last decade, with some lines now using compression-resistant silicone materials that outlast traditional pile by a factor of three. That matters when you are choosing a replacement window. The hardware and sealing system is often a better predictor of long-term performance than the glass package alone.

What San Francisco’s Marine Layer, Fog, and Victorian Housing Stock Mean for Your Windows

San Francisco is not one climate. The Sunset gets fog and salt air. Noe Valley gets more sun and less wind. The Mission runs warmer. The Presidio sits in a wind funnel. Your window and door choices should account for the specific microclimate where you live, not the citywide average. A window that performs well in the Mission may be the wrong window in the Outer Richmond, and the difference is measurable in both comfort and failure rates.

Salt air accelerates corrosion on exposed hardware. Fog brings persistent moisture that sits on sills and frames for hours every morning. Wind drives rain against west-facing elevations with enough force to find every gap in the flashing. And the city’s older housing stock, Victorians and Edwardians with single-pane wood sashes, was never designed for modern glass or modern sealing. Upgrading those windows is not a simple swap. It is a system change, and the system has to account for the wall assembly it lives in.

The practical advice is this: choose glass packages based on orientation. West-facing windows in San Francisco benefit from a low-E coating that reflects afternoon heat while letting in light. Low-E is a thin, nearly invisible metallic coating applied to the glass surface. It reflects infrared energy outward in the summer and keeps interior heat in during the winter. On San Francisco’s west side, where summer fog can make rooms feel clammy and cold, low-E glass raises the interior surface temperature enough to reduce condensation and improve comfort noticeably. East-facing windows, especially in the Mission and Potrero Hill, get morning sun and benefit from a lower solar heat gain coefficient, which is the measure of how much solar radiation passes through the glass. The right product for each exposure is different, and that is why a contractor who carries only one or two manufacturers will spec whatever fits their inventory, not whatever fits your house. The portfolio matters. Eight manufacturer lines means the spec matches the condition, not the other way around.

And yes, the name is a metaphor. A meridian is a fixed line you measure everything against. That is what we mean by it, and it is how we run every installation: a fixed standard, a fixed price, and a written commitment to come back if the work fails within a year. Our Meridian Windows and Doors San Francisco home page has more on how that standard works in practice.

Common Mistakes to Avoid

• Wiping fogged glass and assuming the problem is cosmetic. Between-pane fog does not go away with cleaning. It is a sealed-unit failure, and it only gets worse.
• Ignoring a sticky sash because it only happens in summer. San Francisco’s summer humidity is mild. A sash that binds consistently, even mildly, is telling you something mechanical is wrong.
• Replacing weatherstripping without identifying the draft source first. If the opening was never properly insulated, new weatherstripping will not stop the draft. Run the tissue-test before you spend the money.
• Dismissing a hard-to-latch door as a hinge issue. Check the reveal. If the gap is even and the door is out of plumb, the problem is probably the frame, not the hinges.
• Waiting until a sill is visibly soft to address wood rot. By the time the screwdriver probe sinks, the damage has likely spread further than the visible area. Early repair is a fraction of the cost.
• Signing a contract without a written, itemized price. The price goes on paper before any work starts, always. If a contractor will not put the number in writing, find one who will.
• Buying a window based on price alone. The cheapest window installed poorly costs more than a mid-line window installed correctly. The installation is the product.

When to Call a Professional

Call a professional when the failure involves the building envelope: a saturated wood sill, a window that has shifted out of square, a door that no longer closes against its weatherstrip, or an IG unit that has fogged between the panes. These are not homeowner repairs, and attempting them without the right tools and experience usually makes the problem worse. If you are in San Francisco and you want an honest assessment, Window Installation in San Francisco is where our process starts. Meridian Windows and Doors San Francisco offers free estimates in San Francisco, with the price written down before any work begins. Call (831) 273-7126 to schedule one.

Frequently Asked Questions

The Bottom Line

The warning signs that matter in San Francisco are the ones you can measure without equipment: condensation between panes, a tissue that flutters next to a closed window, a screwdriver that sinks into a sill, a door that is out of plumb with an even reveal, and a sash that drops or sticks more every season. Each of these has a threshold, and the threshold determines whether you are dealing with a five-year problem or a five-month problem. When you reach the point of repair or replacement, get the price in writing before the work starts, and make sure the guarantee is in writing too. For more guides & resources on maintaining your home’s windows and doors, visit our blog. The windows and doors that perform well for decades in this city are the ones that were measured, spec’d, and installed with discipline, not the ones that came with the biggest discount.

If you are in San Francisco and want a straight answer on what your windows and doors need, call (831) 273-7126 to schedule a free estimate. The price goes on paper before any work begins, and the work is covered for 365 days. That is the standard we measure everything against.

Written by Elliot Vance, Owner at Meridian Windows and Doors San Francisco, serving San Francisco since 2009.