Seasonal ADU Care for Los Angeles: Year-Round Homeowner's Guide

Seasonal ADU Care for Los Angeles: Year-Round Homeowner’s Guide

Los Angeles gets roughly 15 inches of rain per year, and nearly all of it falls in about 30 storm events between December and March. That means a minor drainage defect that shows nothing in October becomes a soaked subfloor by February. This guide lays out a seasonal maintenance rhythm built for our specific climate, so you can catch small problems before they turn into five-figure repairs. We’ll walk through the two stress periods that actually matter here, what to check before each one, and how to document the work so your warranty stays enforceable.

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Quick Answer

Seasonal ADU care in Los Angeles comes down to two windows: the Santa Ana wind-and-fire season from October through November, and the rain-and-drainage season from January through March. For a deeper look at what can go wrong year-round, see our ADU Warning Signs: A Los Angeles Homeowner’s Reference Guide. Before each window, run a targeted checklist: roof vent screens, exterior caulk, downspout extensions, area drains, and grading at the slab edge. Do a post-rain inspection in April, and keep a one-line-per-month log. That’s the whole system.

Table of Contents

• Why Los Angeles Has Two Seasons That Matter for ADUs
• The Pre-Santa Ana Checklist: October
• The Rainy-Season Drainage Audit: November Before Storms Arrive
• Summer Heat Management for Detached ADUs
• Spring Post-Rain Inspection: What to Look For
• How to Keep a Seasonal Log That Supports Warranty Claims
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions
• The Bottom Line

Why Los Angeles Has Two Seasons That Matter for ADUs

Every climate has a maintenance calendar, but most of the generic advice online is written for places with snow, ice, and a true freeze-thaw cycle. Los Angeles doesn’t work that way. What we have instead is a dry heat that bakes exterior materials from May through October, then a short, intense wet season that tests every seal, joint, and drainage path those dried-out materials were supposed to protect.

The Santa Ana window runs from October through November. Winds regularly hit 40 to 60 miles per hour in the foothills and canyon communities, and sustained gusts can reach 70 miles per hour in places like Porter Ranch, Sylmar, and the San Gabriel Valley foothills. Those winds carry embers during wildfire season and they also carry fine dust and debris that clogs vent screens and scours exterior caulk. The wind itself is not a structural threat to a properly built ADU, but the gaps it exploits are: a loose vent screen lets embers in, a cracked seal bead opens a path for the January rain that follows.

The rain window runs from January through March, sometimes starting as early as late December. Statistics from the Los Angeles Department of Public Works show that more than 90% of our annual rainfall typically arrives in this period. That concentration is the key insight. An ADU in Los Angeles goes seven to eight months with almost no water exposure, then takes months of accumulated water in a matter of weeks. Any maintenance approach that treats the whole year as one flat checklist misses this rhythm entirely.

If you already have an ADU or are planning one, ADU Builders in Los Angeles can review your site drainage before the next rainy season hits.

The Pre-Santa Ana Checklist: October

The goal here is simple: before the wind season starts, close every gap that wind can exploit and remove every loose item that wind can weaponize. Run this checklist in early October, before the first major wind event. It takes about an hour.

1. Roof vent screens

Check every roof vent and soffit vent for tears, rust, or missing fasteners. A vent screen with a quarter-inch gap is an ember entry point during a wind-driven fire event. In Los Angeles, this is not hypothetical. The 2025 Palisades and Eaton fires pushed embers miles ahead of the flame front, and building code in wildfire-adjacent zones now requires ember-resistant vent openings. Even if you are not in a designated fire hazard severity zone, the same screens keep dust, leaves, and nesting animals out of your attic and wall cavities.

2. Exterior caulk and sealant

Dry heat is the silent killer here. Southern California’s prolonged dry season causes exterior caulk to shrink and crack much faster than in humid climates. Walk the perimeter of your ADU and inspect every joint: window trim to siding, door frames to stucco, penetration points where plumbing or electrical enters the structure. Look for hairline cracks or bead separation. In our experience, south- and west-facing walls show the most failures because they take the strongest daily sun. Recut and re-caulk any failing joint before the winds arrive. This is a one-hour job with a tube of exterior-grade silicone.

3. Loose items in the yard

Anything stored next to the ADU is a projectile in a 60-mile-per-hour gust. Patio furniture, potted plants, garden tools, trash cans, and even stacked lumber get picked up and thrown into the ADU’s siding or windows. Walk the yard and secure or store anything that could move. This is the cheapest insurance you can buy in October.

4. Trees and overhanging branches

A eucalyptus branch overhanging the ADU roof is a Santa Ana accident waiting to happen. Wind-driven branches damage roofing, gutters, and skylights. Trim anything that touches or overhangs the roofline. If the tree is on a neighbor’s property, document the current condition with photos so you have a record.

The Rainy-Season Drainage Audit: November Before Storms Arrive

Do this audit in November, after the Santa Ana checklist but before the first major storm. Water damage in Los Angeles ADUs almost never comes from a dramatic flood. It comes from a slow, steady path that sends water toward the foundation over weeks of rainfall. Here’s the systematic way to check.

Step 1: Start at the roof and gutters

Clean all gutters and downspouts thoroughly. Los Angeles is a dusty city, and eight months of dry deposition fills gutters with silt, leaves, and fine debris. A clogged gutter overflows during the first heavy rain, and that overflow runs down the exterior wall or pools at the foundation. After cleaning, run a garden hose down each downspout to confirm water exits cleanly.

Step 2: Check downspout extensions

The single most common drainage failure we see on Los Angeles ADUs is a downspout that discharges water directly next to the foundation. Every downspout needs an extension or splash block that carries water at least four to six feet away from the structure. If water pools against the slab edge for days, the soil swells, the slab moves, and you get cracks. This is a ten-dollar fix that prevents a ten-thousand-dollar problem.

Step 3: Test area drains

If your ADU sits at the low point of the lot or has a perimeter area drain, test it now. Pour water into each drain and watch whether it moves. A slow-moving or standing drain usually means the line is clogged with roots, silt, or construction debris. In Los Angeles, where many ADUs were built quickly during the post-2017 permitting boom, we regularly find drain lines that were never cleaned after construction. Professional drain cleaning costs a fraction of repairing a water-damaged foundation.

Step 4: Read the grading at the slab edge

Walk the perimeter of the ADU and look at the soil against the foundation. Over time, soil settles, especially if it was backfilled during construction. If the ground slopes toward the ADU anywhere, water will follow that grade. The ideal condition is a visible slope away from the foundation on all sides, with at least six inches of exposed concrete between soil and siding. If you see a low spot or a reversed slope, regrade it now with compacted native soil. Avoid planting dense ground cover directly against the foundation, which traps moisture and hides developing problems.

Step 5: Inspect the crawl space or slab edge

If your ADU has a crawl space, enter it now before the wet season starts. Check for existing moisture, rust, mold, or pest activity. If the subfloor shows signs of previous water exposure, note where the staining sits and trace it upward to find the source. For a slab-on-grade ADU, look for visible cracks at the slab edge and mark any that are wider than the thickness of a nickel. These become leak paths during the rainy season.

If the audit surfaces drainage problems you inherited from a previous build, that’s where a Room Addition Contractor in Los Angeles can step in with a real fix, not a temporary patch.

Summer Heat Management for Detached ADUs

From June through September, Los Angeles regularly hits 90-plus degrees in the San Fernando Valley and inland areas. Detached ADUs have a tougher time than attached structures because all four walls and the roof take full sun exposure, with no shared building mass to buffer the heat. Here’s where mechanical systems work hardest and where failures concentrate.

West- and south-facing exposure

If your ADU faces west or south in a neighborhood like Woodland Hills, Canoga Park, or Northridge, the afternoon heat load is intense. Window glass on those exposures can exceed 130 degrees on the surface, and that heat transfers directly into the living space. Your mini-split or HVAC system then runs harder and longer to compensate. The practical steps: install exterior shade screens or awnings on west-facing windows, use light-colored window coverings inside, and consider planting a deciduous tree on the southwest corner for seasonal shade without blocking winter sun.

Mini-split maintenance

Most Los Angeles ADUs are cooled by ductless mini-split systems. These units are efficient but sensitive to dirty filters and coils. In our experience, a mini-split with a clogged filter runs 15 to 20 percent harder than it should, and that extra load shortens the compressor’s life. Clean or replace the filters every month during peak cooling season. Once a year, schedule a professional coil cleaning. If you have never had the coils cleaned and the unit is more than three years old, do it now. The service costs between $120 and $250 and pays for itself in reduced energy use and longer equipment life.

Roof and attic ventilation

Heat that builds up in the roof assembly radiates downward into the living space all night. If your ADU has an attic, check that ridge vents, gable vents, or powered ventilators are working correctly in July. A hot attic also accelerates the aging of roofing materials. If the attic is unconditioned and the roof is older, inspect for signs of sagging or cracked shingles after a heat wave. Reflective roof coatings and cool-roof materials are now standard on many prefab ADUs from manufacturers like Abodu and Cover, and they materially reduce the heat load on the structure.

Expansion and contraction cycles

Los Angeles heat cycles put real stress on exterior materials. Fiber cement siding from James Hardie holds up well because it is engineered for thermal movement, but the caulk joints between siding courses and around windows are still the weak point. After a summer of 100-degree days and 60-degree nights, those joints have opened and closed dozens of times. The October caulk check we described above is the direct follow-up to this section. What the summer expands, the fall caulk crew closes.

Spring Post-Rain Inspection: What to Look For

April is the month to walk around the ADU with a flashlight and a notepad. The wet season is over, and whatever happened during those storms is now visible. This inspection is what turns the previous two checklists from maintenance into documentation. Here is what matters.

Crawl space after a wet winter

If your ADU has a crawl space, enter it in April and inspect the subfloor for any sign of water stains, mold, or standing water. Winter rain that saturated the soil can wick up through the foundation for months afterward. Look at the rim joists particularly, where the floor meets the outer walls. Dark staining, white efflorescence, or a musty smell means water got in somewhere. Trace it now while the evidence is fresh.

Slab edge and hairline cracks

For a slab-on-grade ADU, walk the perimeter and re-check every crack you noted in November. If a crack widened over the winter, or if a new crack appeared, pay attention to the direction. Vertical cracks under a wide of about one-eighth of an inch are usually settlement and should be monitored. Horizontal cracks, or cracks with visible displacement on one side, are different. Those need a foundation specialist to look at them. Mark each crack with a pencil line and the date so you have a baseline for next year.

Stucco and siding after wind-driven rain

Los Angeles rain often comes sideways during a storm, driven by wind against the walls. Check for moisture staining around window frames, under eaves, and where the siding meets the foundation. On a stucco ADU, small hairline cracks that show up in April are often the result of water penetration followed by drying. If the stucco sounds hollow when tapped, water may have gotten behind it. This is also the right time to re-caulk any joints that opened during the rainy season.

Landscape and irrigation

After a wet winter, sprinkler timers are often still set as though it were August. Overwatering in spring is the most common cause of standing water near the ADU foundation, and it mimics a drainage failure. Reprogram the irrigation controller for lower spring settings, and check that sprinkler heads are not spraying directly onto the ADU walls. Water hitting stucco or siding repeatedly is a slow path to rot and termite activity.

How to Keep a Seasonal Log That Supports Warranty Claims

When something fails on an ADU, the homeowner’s most valuable document is a log showing that maintenance was performed on schedule. Insurance claims and warranty claims both go smoother when the homeowner can produce a dated record of inspections and repairs. This does not have to be complicated. A single page per season is enough.

1. Create a simple spreadsheet or notebook. Columns: Date, Season, Area Checked, What We Found, What We Did, Cost. That’s all.
2. Log every inspection in the same month it happens. October for Santa Ana prep, November for drainage, April for post-rain. Consistency makes the record credible.
3. Include photos. Take three or four photos during each inspection: the roof vent screens, the downspout extensions, the slab edge, the crawl space. Store them in a folder named by date. A photo with a timestamp is stronger than a written note.
4. Record every professional service call. HVAC cleaning, drain cleaning, roof inspection, termite treatment. Note the company, the date, and what was done. Keep the invoice.
5. Attach repair receipts to the log. If you re-caulked a window or replaced a downspout extension, staple the hardware store receipt to the log page. The combination of dated notes and receipts is hard to dispute.

A well-kept log also supports warranty claims. The Garrison Standard, the standard behind Fielding ADU Los Angeles, covers workmanship defects for a full year from project completion. When a homeowner can show a dated record of proper seasonal maintenance, the warranty discussion becomes much simpler. Documentation answers the usual question: did the homeowner do their part, or was the problem caused by neglect?

If you’re planning a new ADU and want to know what a warranty actually covers, talk to us about Garage Conversion Contractor in Los Angeles work. Our written guarantee spells out exactly what’s covered and for how long, no fine print buried on page seven.

Common Mistakes to Avoid

• Skipping the October caulk check because the weather is nice. The dry months are exactly when caulk cracks open, and the October check is the last good opportunity to close those gaps before the wind and rain arrive. Missing it means the February storm finds every opening you left.
• Assuming the downspouts are working because water comes out. What matters is where the water goes after it exits the downspout. A downspout discharging six inches from the foundation is doing harm even when it flows freely. Check the extension, not just the pipe.
• Watering the landscape on the same schedule all year. A sprinkler system set for August output will soak the soil around the ADU foundation all through March and April, creating exactly the moist conditions that attract termites and undermine the slab. Reprogram the controller by season.
• Ignoring a small crack because it has not caused a problem yet. A crack at the slab edge is a path for water. What begins as a hairline in November becomes an open channel by March when rain water pools and presses against the foundation. Mark it, monitor it, and fix it before the wet season.
• Not documenting maintenance because it feels unnecessary. When a warranty claim or insurance claim gets disputed, the homeowner without a log is arguing from memory. A one-page log per season is ten minutes of work that can save thousands of dollars in a claim denial.
• Storing loose items against the ADU during wind season. That stack of lumber leaning next to the ADU is a missile when the Santa Anas hit. Anything that can move will move, and the ADU’s siding or windows are what stops it.

When to Call a Professional

Most of the seasonal maintenance in this guide is homeowner-manageable with basic tools and an hour of time. But some conditions call for a trained eye. If you find water staining inside the crawl space with no obvious source, or a slab crack that has widened over a single season, do not guess at the fix. Those are structural questions. If your drainage audit uncovers a clogged area drain line that will not clear with a garden hose, the line probably needs mechanical cleaning. If your mini-split iced over during summer or blows warm air during a heat wave, the refrigerant or compressor needs professional attention.

Fielding ADU Los Angeles offers free estimates in Los Angeles for seasonal maintenance, drainage corrections, and ADU repairs. Call (213) 732-1415 and describe what you found. We’ll tell you whether it is worth a service visit.

Frequently Asked Questions

The Bottom Line

Los Angeles does not have four seasons, but it has two that matter for your ADU: the Santa Ana wind window and the winter rain window. Preparing for each one takes about an hour twice a year, plus a shorter check in July and a documentation pass in April. The total cost is under $500 annually when things are in good shape. The alternative is a drainage failure or wind-driven water intrusion that costs ten to fifty times that amount to repair. Keep the log, close the gaps, and get the water away from the foundation. Do that, and the structure will outlast most of what the city throws at it.

Written by Reed Calloway, Owner at Fielding ADU Los Angeles, serving Los Angeles since 2006.