Seasonal Windows & Doors Care for San Francisco: Year-Round Homeowner's Guide

Seasonal Windows & Doors Care for San Francisco: Year-Round Homeowner’s Guide

The Diablo winds that arrive in September and October, dry, fast, and capable of driving particulate into every weatherstripped gap, cause more sudden seal and finish damage to San Francisco windows and doors than the entire rainy season that follows. Yet almost no maintenance guide mentions them. This guide rebuilds the seasonal care calendar around San Francisco’s actual weather rhythm, not a generic national template, and pairs well with our Window Replacement Maintenance Checklist for San Francisco Homeowners. You’ll learn exactly what to check during each of the city’s four distinct phases, when to act, and what can wait. If you own a home in San Francisco, the schedule below will save you money on repairs that most homeowners only discover after water has already found a way in.

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Quick Answer

Seasonal window and door care in San Francisco means timing your maintenance to four local phases: fog season (June – September), fire wind season (October – November), rainy season (December – March), and dry spring (April – May), a schedule shaped by the Windows & Doors Permits, Codes & Inspections in CA: What You Need to Know requirements that govern major repairs. The most critical window is the 48 hours after a Diablo wind event, when you should inspect east-facing seals, tracks, and finishes for particulate damage before winter rain turns small gaps into sill rot. Maintain interior humidity between 45 – 55% RH during July and August to prevent condensation-related frame damage, and re-lubricate door and window hardware every 3 – 6 months depending on your proximity to salt air.

Table of Contents

• Fog Season Maintenance (June – September): Managing Moisture When It Never Rains
• Fire Wind Season (October – November): The 48-Hour Post-Diablo Inspection
• Rainy Season (December – March): Keeping Water on the Outside Where It Belongs
• Dry Spring (April – May): Swollen Frames, Re-Squaring, and Hardware Recovery
• Hardware Lubrication: A San Francisco Salt-Air Schedule
• Fog-Season Condensation: Why Interior Humidity Matters More Than Window Quality
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions
• The Bottom Line

Fog Season Maintenance (June – September): Managing Moisture When It Never Rains

San Francisco’s fog season runs from June through September, and it creates a maintenance problem that homeowners in drier climates never face: persistent exterior moisture without any actual rainfall. Windows and doors in the Richmond, Sunset, and Twin Peaks districts sit in fog for hours each day, and that fog deposits a fine saline film on glass, frames, and hardware. The salt in that film is hygroscopic, meaning it draws more moisture from the air and holds it against the surface. Over a single summer, this cycle can pit aluminum frames, cloud low-quality glass coatings, and corrode door hinges that were not rated for coastal exposure.

Here is the fog-season routine we recommend for every home in San Francisco, with timing that reflects how fog actually behaves here:

1. Mid-June, after the first sustained fog bank: Wash all window glass and door glass with a mild detergent and a soft cloth. Do not use ammonia-based cleaners on coated glass; they degrade low-E films over time. Rinse thoroughly, because residue from the cleaner will hold fog moisture longer than clean glass would.
2. July 1 – 15: Inspect all exterior caulk beads and weatherstripping for the first signs of mildew or salt crystallization. Pay closest attention to west-facing surfaces, which get the most direct fog contact in San Francisco.
3. August, during the warmest inland afternoons: Open windows during the two or three hours of afternoon sun when the fog has pulled back. This is not about “airing out” in a general sense; it is the only reliable window in the city’s summer calendar when exterior surfaces can fully dry, and dry surfaces resist mildew and salt adhesion.
4. Late September, before fire winds begin: Check every door sweep. Fog-season moisture softens the rubber on sweeps and makes them more likely to tear when dry winds begin to push debris against them. A torn sweep in September becomes a dust entry point in October.

One thing we see often when visiting homes for Window Replacement in San Francisco is fog-season damage that was written off as “normal coastal wear.” Mildew staining on interior window sills is not normal for any home, regardless of how close it is to Ocean Beach. It is a signal that exterior seals are no longer keeping fog moisture out, and the fix is usually straightforward if caught before the rainy season adds pressure-driven water to the mix.

Fire Wind Season (October – November): The 48-Hour Post-Diablo Inspection

The Diablo winds that arrive in September and October are the single most destructive seasonal force acting on San Francisco windows and doors. They are dry, fast, and loaded with fine particulate from inland hillsides, and they attack homes from the east and northeast, which is the opposite direction of every other weather system in the city. That directional reversal is why so many homeowners miss Diablo damage: they are used to checking the fog-facing west side, while the east-facing windows and doors absorb the brunt of the wind.

Here is what Diablo events do to specific components:

• Weatherstripping adhesion: The combination of heat (often 80 – 90°F during an event) and particulate abrasion causes adhesive-backed weatherstripping to peel at the edges. Once a strip lifts, wind gets behind it and tears it further. We have seen east-facing doors in Bernal Heights lose entire weatherstripping runs in a single strong event.
• Door hardware: Fine dust works its way into deadbolts, hinges, and strike plates. This dust is not inert; it contains alkaline soil particles that accelerate corrosion on brass and steel hardware. A deadbolt that turns stiffly in October will seize entirely by December if not cleaned and lubricated.
• Exterior finish: Aluminum-clad window frames and painted door slabs get sandblasted by airborne particulate. The damage looks like fine horizontal scratches across east-facing surfaces, and once the finish is compromised, winter moisture has a direct path to the underlying material.
• Screen and track debris: Sliding door tracks fill with wind-driven grit, and that grit grinds against rollers every time the door is opened. Most roller failures we repair in San Francisco homes trace back to Diablo-season grit, not normal wear.

The 48-hour post-event inspection is the highest-leverage maintenance habit in this entire guide. Do this:

1. Within 24 hours of a major Diablo event ending, walk every east-facing window and door. Run your hand along each weatherstripping edge. If you feel any lifted section, press it back and photograph it. If it does not stay down, it needs replacement, not a temporary fix.
2. Open and close every east-facing sliding door and window three times. Listen for grinding. If you hear it, do not continue cycling the door; grit is already in the roller assembly and every cycle deepens the damage.
3. Vacuum every sliding door track and window track with a narrow crevice tool. Do not use compressed air to blow the track clean; it drives grit deeper into the roller housing. A vacuum with a soft brush attachment lifts the debris out without forcing it inward.
4. Test every exterior lock and latch. If any lock feels gritty or stiff, clean the mechanism with a dry brush, then apply a small amount of the correct lubricant (see the hardware lubrication section below).
5. Check window and door perimeter seals for visible dust streaking on interior surfaces. If you see a fine line of dust on the interior sill or floor directly beneath a closed door, the seal is already failing, and that dust is a preview of exactly where rainwater will enter in December.

This inspection takes about 30 minutes. It catches 80% of wind-related damage before it becomes water-related damage, and it is the single most valuable thing you can do for your home in October.

Rainy Season (December – March): Keeping Water on the Outside Where It Belongs

San Francisco’s rainy season is not the hardest rain in California, but it is the hardest rain that falls on the city’s windows and doors, because it falls sideways. Rain driven by Pacific storms hits the west and southwest sides of homes at an angle, and any gap in exterior calk, weatherstripping, or flashing becomes a channel for water that gravity alone would never have found. The neighborhoods that see the most wind-driven rain damage are the Sunset, Parkside, Outer Richmond, and anything on the western slope of Twin Peaks.

The December – March window and door care routine is about verification, not modification. You should not be applying caulk or installing new weatherstripping during a rainstorm. But you should be testing everything you prepared in October and November, and the rainy season is when you learn whether that preparation was sufficient.

Here is the rainy season checklist, keyed to the actual storm pattern in San Francisco:

1. During the first heavy rain of December: Walk every room with exterior windows and doors. Check the interior sill, frame, and floor beneath each opening for moisture. A darkening of the wood, a paint bubble, or a visible bead of water means the exterior seal is failing. Mark the location, photograph it, and plan to address it in the spring dry-out window.
2. After each major storm (wind plus rain): Repeat a shortened version of the Diablo inspection on the windward side. Storms in San Francisco are rarely rain-only; they carry gusts that re-open small seal failures.
3. January, during a dry spell: If you see a clear 3 – 4 day dry window, inspect all south-facing and west-facing exterior caulk. This is the wettest side of most San Francisco homes, and any caulk that is cracked, chalky, or pulling away from the frame will fail before March.
4. February, after the coldest weeks: Check for condensation on the interior side of window glass in bedrooms and bathrooms. Some condensation is normal after a cold night, but if it persists past mid-morning, the moisture load in the home is too high and you are on a path to sill rot. Run a dehumidifier or improve bathroom ventilation before March.
5. Late March, before dry spring: Inspect wood door frames and wood window sills for swelling. It is normal for wood to absorb moisture during the rainy season, but the dimensional changes are a signal worth recording, because they tell you what to expect in April.

One more note on this season: if you have storm windows or storm doors, San Francisco’s rainy season is the only time of year they should be in place. A storm window installed over a leaking primary window is not a repair; it is a temporary bandage that hides the problem. If you find yourself relying on storm windows to stay dry, the primary window needs Window Installation in San Francisco or a serious seal refresh. The rainy season should be the season when your primary seals do the work.

Dry Spring (April – May): Swollen Frames, Re-Squaring, and Hardware Recovery

April and May in San Francisco are the season of recovery. The rain has stopped, the fog has not yet arrived in force, and the air is dry enough to reveal exactly how much moisture every wood component absorbed during the winter. This is the only window in the city’s calendar when you can safely evaluate and repair swollen frames, re-square doors, and restore hardware that the rainy season corroded.

The key question every homeowner faces in April is this: is the wood frame swollen, or is it permanently distorted? The answer matters because swollen frames recover on their own, while permanently distorted frames need professional re-fitting or replacement.

Here is how to tell the difference:

1. Measure the gap. If a wood door sticks along the top edge or latch side, measure the visible gap between the door slab and the frame at three points: top, middle, bottom. Write down the numbers.
2. Wait two weeks of dry weather. If the gap measurements return to within 1/16 inch of what they were before the rainy season, the frame has rebounded and no adjustment is needed. This is normal seasonal movement.
3. If the door still sticks after two weeks of dry air, the frame has permanently distorted. In our experience, the most common cause in San Francisco homes is not the frame itself but the way water was directed to it. A failed exterior caulk bead at the top of the frame lets water run behind the casing and soak the rough opening, and once the rough opening framing absorbs that water, the door frame can twist permanently.
4. Inspect the hinges before you plane anything. A door that sticks at the top on the latch side but has loose hinge screws is a hinge problem, not a frame problem. Tighten every hinge screw, and if any screw spins without resistance, replace it with a longer screw that catches the king stud behind the jamb.

Re-squaring a door in San Francisco is a judgment call. If the door slab is solid and the frame is only slightly out of square (less than 1/8 inch of cumulative gap change), a professional can often correct it by adjusting hinges, adding a thin shim behind the jamb, or lightly planing the binding edge. If the frame is out of square by more than 3/16 inch and the door is an exterior door, replacement of the slab and frame is usually more cost-effective than repeated re-mortising, because the frame’s structural connection to the rough opening has already been compromised. Most Door Installation in San Francisco projects we do in April and May are replacements for exactly this kind of cumulative water damage, often with a Therma-Tru or Mr-Glass door chosen for better moisture resistance on the weather side.

Hardware Lubrication: A San Francisco Salt-Air Schedule

Hardware lubrication is the least glamorous part of window and door care and the most commonly skipped. In San Francisco, your lubrication schedule should be based on your distance from salt air, not on the calendar alone. The city’s fog carries salt inland, and that salt accelerates corrosion on hinges, rollers, locks, and track hardware.

Here is a practical schedule for San Francisco addresses:

• Within 5 blocks of the ocean or bay: Lubricate all moving window and door hardware every 3 months, year-round. The salt load is highest here, and even stainless steel will eventually show pitting if it is not maintained.
• 5 to 15 blocks from the water: Lubricate every 4 months. The difference in corrosion rate between a house in the Outer Sunset (fog-saturated, salt-heavy) and one in the Inner Sunset (less fog, less salt) is substantial, but both need more frequent attention than inland homes.
• East side of the city, more than 15 blocks from the bay: Lubricate every 6 months. Diablo winds still deposit grit on your hardware, so do an extra lubrication pass in late October after the first strong wind event.

The lubricant you choose matters more than the schedule. Use a silicone-based lubricant on metal-to-metal contact points: hinges, rollers, sliding door tracks, and deadbolt internals. Silicone does not attract dust the way petroleum-based lubricants do, and dust attraction is the exact problem you are trying to prevent after a Diablo event. Use a petroleum-based lubricant only on parts that need a heavier film and are not exposed to airborne grit, such as door closer internals. And never use WD-40 on window or door hardware; it is a water displacer, not a long-term lubricant, and it leaves a residue that hardens and makes the original problem worse.

Fog-Season Condensation: Why Interior Humidity Matters More Than Window Quality

The foggiest months in San Francisco, July and August, are also the months when homeowners report the most interior window condensation. The instinct is to blame the windows, but the physics of the situation is different: fog-season condensation is primarily an interior humidity problem, not a window quality problem. When outdoor air is 55 – 60°F and saturated with fog moisture, and indoor air is 68 – 72°F with normal household humidity, the dew point can form on any window surface that has even modestly cool glass. The highest-efficiency window in the world will still show condensation if the indoor relative humidity is too high for the outdoor temperature.

The target range for San Francisco homes during July and August is 45 – 55% relative humidity. Below 45%, you get dry air that irritates skin and respiratory passages. Above 55%, you are inviting condensation on every window with a cool surface, and that condensation is what causes sill rot over time.

Here is what drives interior humidity up in July and August in San Francisco:

• Showering without running a bathroom exhaust fan. A single hot shower can add 8 – 10% RH to an average bathroom, and if that bathroom has no exterior window, the moisture has nowhere to go except inward through the house.
• Cooking without a range hood that vents to the outside. Most San Francisco kitchens have recirculating hoods that do not remove moisture. Boiling a pot of pasta with a recirculating hood adds visible humidity to the whole floor.
• Drying laundry indoors. Many San Francisco homes have no outdoor drying space during fog season, and indoor drying racks can push interior RH from 50% to 65% in an afternoon.
• Not running a dehumidifier in below-grade rooms. Basements and ground-floor units in the Marina and Mission districts often sit at 60 – 65% RH year-round, and that moisture migrates upward.

Keeping a small hygrometer in the living room and bedroom costs under $15 and gives you the number you need. If the reading is above 55% during July and August, address the moisture source before you spend money on new windows. The window is rarely the problem in fog season; the air in the house is. When the humidity is under control and condensation still forms on the interior, that is when we start looking at the window’s thermal performance. A window from ECO Window Systems or ViewLux with a proper low-E coating and warm-edge spacer will perform measurably better than a 20-year-old double pane that has lost its gas fill, and the difference is most visible during fog season, when the gap between interior and exterior conditions is narrow but persistent.

Common Mistakes to Avoid

• Following a national seasonal checklist. San Francisco does not have a “fall maintenance weekend” in October; October is when dry winds arrive and demand an inspection, not a gutter-cleaning session. A national template will have you cleaning gutters while your east-facing weatherstripping is peeling away unnoticed.
• Ignoring east-facing windows and doors. Most damage in San Francisco comes from the east during fire wind season and the west during winter storms, but the east side is the one homeowners forget to check, because it looks fine during the rest of the year.
• Using ammonia-based glass cleaner on coated glass. In a city where fog-season cleaning matters as much as it does in San Francisco, the cleaner you choose matters. Ammonia degrades low-E coatings and shortens the life of the glass package.
• Applying caulk during the rainy season. Caulk needs a dry, clean surface to bond, and San Francisco’s rainy season does not provide that. Caulk applied in December fails by February, and you have added a peeling bead on top of a leak that was already there.
• Lubricating hardware without cleaning it first. In San Francisco, the grit you lubricate into a door hinge during October stays there and acts like sanding compound for the rest of the year. Clean the hardware, then lubricate.
• Waiting until a door sticks to check the hinges. A door that sticks in April has been telling you something since December. Loose hinges and failed caulk show up weeks before the door stops closing, and the earlier you catch them, the less money leaves the bank.
• Assuming fog damage is normal. Salt film on glass, mildew on sills, and pitted aluminum are all correctable with the right maintenance and the right materials, not inevitable consequences of living in the Sunset or Richmond.

When to Call a Professional

Some window and door care is safe to do yourself, and some is not. Call a professional if you see water entering the home through a window or door that was sealed six months ago, if a wood frame is out of square by more than 3/16 inch after the dry spring recovery period, if weatherstripping peels away on multiple openings after a single wind event, or if any door or window hardware fails completely. Replacing a failed seal on an east-facing window in San Francisco is not a caulk-and-hope job; it is a moisture-management repair that needs the right materials and the right sequence. Lightwell Windows San Francisco offers free estimates in San Francisco, call (831) 480-4124, and every estimate comes with a written price before any work starts.

Frequently Asked Questions

The Bottom Line

San Francisco’s calendar does not fit the national maintenance template, and treating it as if it does will cost you money. The city’s four distinct phases, fog, fire wind, rain, and dry spring, each demand a specific set of window and door tasks, and the most important one is the 48-hour inspection after a Diablo event. Keep indoor humidity between 45 – 55% during July and August, lubricate hardware on a salt-air schedule rather than a calendar schedule, and address spring swelling before it becomes permanent frame distortion. If you catch the seasonal failures early, you will never see the inside of a water damage repair bill. And if you are not sure what you are looking at, Lightwell Windows San Francisco home is here to take the call.

Written by Keith Yamada, Owner at Lightwell Windows San Francisco, serving San Francisco since 2010. Browse more guides & resources for Bay Area homeowners.