ADU Warning Signs: A San Diego Homeowner's Reference Guide

ADU Warning Signs: A San Diego Homeowner’s Reference Guide

A hairline crack in drywall is usually nothing. A hairline crack that runs at 45 degrees from a door corner, reappears after being patched, and is accompanied by a door that sticks seasonally is a foundation movement indicator – and in San Diego’s expansive soil zones, that distinction matters more than most homeowners realize. This guide is organized by symptom, not by trade. You don’t need construction vocabulary to use it. You need to know what to look for, what it means, and when it’s time to call someone who fixes it for a living.

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Quick Answer

Most ADU problems in San Diego show visible warning signs months before they become expensive failures. The signs to watch are diagonal cracks from door and window corners, musty odors that persist after airing out, breakers that trip under normal load, and water staining on stem walls or below windows. Document what you find with photos and dates, check whether your warranty covers it, and call a licensed ADU contractor in San Diego for an assessment before a $400 fix becomes a $14,000 repair.

Table of Contents

• Structural Cracks vs. Cosmetic Cracks: How to Tell the Difference
• Moisture Warning Signs Specific to San Diego ADUs
• Electrical Warning Signs in ADUs and Converted Garages
• When a Mini-Split Is Failing: What You’ll Notice First
• How to Document a Warning Sign the Right Way
• Warranty Claims vs. Normal Wear: What You Own and What the Contractor Owns
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions
• The Bottom Line

Structural Cracks vs. Cosmetic Cracks: How to Tell the Difference

Drywall cracks are the most common thing we’re asked about in San Diego ADUs, and most of them are harmless. Drywall expands and contracts with humidity, and San Diego’s marine layer brings enough moisture swing that hairline cracks along taped seams are normal, especially in the first two years after construction. The drywall compound dries, the framing settles a fraction of an inch, and a thin vertical line appears along a seam.

Structural cracks behave differently. They follow a pattern, they have a location, and they come back.

Here’s what separates the two:

• Pattern: Cracks that run straight up and down or straight across, following a drywall seam, are typically cosmetic. Cracks that angle at 30 to 45 degrees from a door corner or window corner are following stress, not a seam. That’s foundation or framing movement.
• Location: Seam cracks appear in the middle of walls. Structural cracks cluster at openings – doors, windows, and the corners where a wall meets the ceiling. Openings are where framing transfers load, and that’s where movement shows first.
• Recurrence: You patch a cosmetic crack once and it stays gone. A structural crack comes back within a season, sometimes wider. In San Diego, lots of homeowners see recurrence after the winter rains, when clay-heavy soils in neighborhoods like Clairemont and parts of East County absorb water and swell, then shrink in the summer heat.
• Width: A crack you can slip a dime into – roughly 1/16 inch – is worth having looked at. Anything approaching 1/8 inch demands a professional assessment.

Doors that stick seasonally are another tell. A door that binds in January and swings freely in August is responding to soil movement beneath the slab. In a detached ADU on a raised foundation, the same movement shows up as slight gaps between exterior siding boards or pavers pulling away from the stem wall. We’ve seen these exact patterns on garage conversions across San Diego, especially where the original garage slab predates the ADU by decades.

If you’re comparing build methods, our DIY vs Professional ADU: The San Diego Homeowner’s Decision Guide breaks down how prefab platforms like Abodu and Cover engineer their foundations for specific soil conditions before the module ever arrives. A conventional build that skips a soils report can put you in the position of watching a brand-new ADU develop foundation issues within the first three years. In San Diego’s expansive soil zones, that soils report is not paperwork. It’s the difference between a structure that moves and one that stays put.

One more thing worth knowing: the ADU builders in San Diego who put the price in writing before work starts are also the ones who’ll specify foundation requirements honestly, because they know they’re standing behind the structure for a year after the final walkthrough. If a builder skips the soils conversation, ask why.

Moisture Warning Signs Specific to San Diego ADUs

San Diego gets about 10 inches of rain a year, and most of it falls between December and March. That concentrated wet season is when moisture problems in ADUs announce themselves. The signs are visible if you know where to look.

Efflorescence on Stem Walls

Efflorescence is that chalky white powder that appears on concrete or masonry after water moves through it and evaporates, leaving mineral salts behind. On a stem wall, it means water is wicking up from the soil or sitting against the foundation. You’ll see it most often after the rainy season, particularly on the north side of a structure that never gets direct sun. In San Diego neighborhoods with older lots – parts of Normal Heights, North Park, and the pocket neighborhoods east of Balboa Park – stem walls on the original home can be decades old, and the same soil moisture that affects the main house will affect a new JADU or detached ADU sitting on the same lot.

Efflorescence itself is not structural damage. But it’s a map. It shows you exactly where water is traveling, and if it’s on a stem wall that supports a new ADU, the source needs to be found – often a downspout that discharges too close to the foundation or a grade that slopes toward the building instead of away.

Rust Staining Below Windows

Rust-colored streaks running down from window corners or sill edges are a specific and common sign in coastal San Diego. Salt air accelerates corrosion on any exposed metal – window flashing, sill brackets, even the heads of screws used in trim. When you see rust staining, water is getting behind the window’s weather barrier and carrying corrosion out with it. The leak is above the stain, not below it. Left unchecked, this rots the framing around the window and eventually shows up as soft drywall inside.

This is one place where material choice matters. Builds using quality cladding systems – including those that integrate James Hardie fiber cement siding – hold up measurably better against coastal moisture than wood lap siding. If you’re planning an ADU within three miles of the coast, ask your builder how they detail window flashing. If they describe a generic sealant-and-tape approach, they don’t build near salt air.

Musty Odor in a JADU That Shares a Garage Wall

Junior ADUs, by code, are often attached to or converted from garage space. That means one wall of your living space is the old garage wall. Garages are not built to the same moisture standard as living space. The slab is often thinner, the wall assembly may not include a proper vapor barrier, and the air gap between the garage and the living space can trap humidity.

If you walk into a JADU and smell a musty, closed-up odor that doesn’t resolve after opening windows for a day, don’t mask it with air freshener. That smell is active mold or mildew in the wall cavity or under the flooring. The first place to look is the base of the shared wall, where garage-slab moisture wicks upward. This is one of the most common findings in our garage conversion work across San Diego, and it’s almost always correctable if caught early – typically by addressing drainage, ventilation, or the vapor barrier. Caught late, it’s a gut-and-replace on the affected wall.

Electrical Warning Signs in ADUs and Converted Garages

Electrical failures rarely happen without warning. The signs are there, but they’re easy to dismiss because they’re intermittent.

Breakers That Trip Under Normal Load

A breaker trip is a safety feature working. One trip, shortly after you plug in a space heater and a hair dryer on the same circuit, is the breaker doing its job. But when a breaker trips repeatedly under ordinary load – a window AC unit on a dedicated circuit, or a microwave on a kitchen circuit with nothing else running – that’s a warning sign. The circuit is overloaded, the breaker is aging out, or there’s a wiring fault.

In converted garages, the original electrical panel was not designed for a living space. A garage built in the 1970s or 1980s typically had a single 20-amp circuit for a garage door opener and an outlet. Convert that garage to an ADU and you’re now running lights, a kitchenette, a bathroom fan, and a mini-split on infrastructure that was never rated for it. The breakers let you know.

GFCI Outlets That Won’t Reset

A GFCI outlet that refuses to reset is trying to tell you something specific: there’s a ground fault somewhere on that circuit, or the outlet itself has failed. The test is simple. If you reset it and it instantly trips again with nothing plugged in, you have a wiring problem, not an outlet problem. If it won’t reset even after being unplugged from everything, the outlet is done and should be replaced.

In San Diego, GFCI protection is required by code for any outlet within six feet of a water source, plus all outlets in a garage-converted space. If your ADU’s bathroom outlet, kitchen counter outlet, and exterior outlet are all on the same GFCI circuit, a single ground fault kills all three. That’s legal, but it’s a sign of a builder who consolidated to save money on breakers. We spec separate GFCI circuits on ADU builds because we’ve spent too many hours tracing ground faults across San Diego garages that should have been on their own circuits from day one, and our guide on How to Hire a ADU Contractor in San Diego: A Step-by-Step Guide explains what to ask about electrical planning before you sign.

Aluminum Wiring in Older Garage Conversions

Here’s one that’s specific to converted garages. If the original garage was built between roughly 1965 and 1972, it may have aluminum branch wiring. Aluminum expands and contracts with heat more than copper, which loosens connections over time. Loose connections arc. Arcs cause fires. The visible signs are warm outlet covers, flickering lights when an appliance cycles on, or a faint burning-plastic smell near an outlet that comes and goes.

If you’re converting a garage from this era, the wiring needs to be evaluated by an electrician before any drywall goes up. The same applies if you’re buying a home in San Diego with an existing ADU that was converted from a garage in the 1980s or earlier. Pull one outlet cover. If the wire is silver, not copper, budget for remediation.

When a Mini-Split Is Failing: What You’ll Notice First

Mini-split systems fail slowly and predictably. They don’t usually die overnight. Here’s the order in which the warning signs typically appear:

1. Reduced cooling output: The unit runs constantly, blows cool but not cold air, and the room never quite reaches the set temperature. This can be a refrigerant charge issue or a dirty evaporator coil.
2. Water staining or dripping below the indoor unit: The condensate drain line is the first place to check. Dust, mold, and insects clog it, especially in San Diego’s dry season when the line dries out and whatever’s inside hardens into a plug. When the next humid period hits, the water backs up and runs down the wall.
3. Gurgling or bubbling sounds during operation: That’s condensate moving sluggishly through a partially clogged drain pan. The pan is full and draining on a delay.
4. Musty odor from the indoor unit: Standing water in a partially blocked drain pan grows biological material. The fan blows that odor into the room every time it cycles.
5. Ice on the refrigerant lines or coil: Ice means the system is starving for airflow or low on refrigerant. Either way, it’s working harder than it should be and wasting power while it does it.

The drainage pan and condensate line are where most mini-split problems begin. It’s a $150 service call when caught early. It’s a wall repair and possibly a new indoor unit when the water has been running inside the wall cavity for a month. In San Diego’s dry climate, homeowners often ignore a mini-split warning sign because the unit still cools on the hottest days. That’s the trap. A system that’s cooling at 70% capacity feels fine until August, and by then the condensate issue has had three months to do its quiet damage.

If you’re planning an ADU, ask your contractor how they route and size condensate lines. A room addition contractor in San Diego who regularly installs mini-splits will have a specific answer about line diameter, slope, and access points for cleaning. A builder who treats the mini-split as an afterthought is a builder whose one-year warranty you’ll be calling in.

How to Document a Warning Sign the Right Way

Documentation is the difference between a warranty claim that gets resolved and one that drags on. Here’s the method that works:

1. Photograph first, before anything moves. Take a photo from at least three feet away so the full context is visible – which wall, which room, what’s nearby. Then take a close-up. Use a coin or a ruler in the close-up for scale. Your phone timestamps the photo automatically, which gives you the date.
2. Take a short video walkthrough. Pan slowly from the wide shot to the close-up. This eliminates any dispute about where the issue is.
3. Write down three things: the date you first noticed it, what you were doing when you noticed it, and whether anything changed in the week before – rain, heat wave, new appliance, landscaping work near the foundation.
4. Add a measurement. For cracks, measure width with a ruler. For moisture, note the exact spot. For electrical issues, note which breaker, which outlet, and what was running.
5. Create a folder. Store everything in one place – a cloud folder or a physical file. If the issue recurs, you now have a before and after. That recurrence evidence is what separates a covered warranty claim from a he-said-she-said.

This documentation matters even if you don’t have a warranty. A structural issue in a San Diego ADU that goes unaddressed can become a disclosure problem when you sell. Having dated photos and notes shows you acted in good faith and gives the next owner a clear history.

Warranty Claims vs. Normal Wear: What You Own and What the Contractor Owns

Every ADU has a warranty period, and every warranty has limits. Understanding where the line falls saves you from filing claims that waste time and from eating costs you shouldn’t have to own.

The contractor owns:

• Workmanship defects: cracks in new stucco or drywall that appear within the warranty window and follow the pattern of movement or installation error
• Code violations: anything that fails inspection or is found to have been built outside the permitted plans
• Material defects covered by the manufacturer’s warranty, which the contractor should facilitate
• Failure of installed systems: a mini-split that fails from improper installation, a roof that leaks from improper flashing, a door that was hung out of square

You own:

• Normal wear: scuffs, paint fading, caulk shrinking, minor settling cracks that stay under 1/16 inch and don’t return after patching
• Maintenance: cleaning the mini-split filter, keeping the condensate line clear, maintaining the grade around the foundation
• Damage from use: a window cracked by impact, a screen torn by a dog, a cabinet door pulled off its hinge
• Anything a previous owner modified after the original build

The Garrison Standard – the operating code behind Fielding ADU San Diego – puts the warranty in writing before work starts and covers defects for a full 365 days. If the work fails inside that year, we come back and correct it at no charge. That’s the standard Reed Calloway built the company around. Not every San Diego contractor offers a written one-year guarantee on ADU work, and the difference shows up when a warning sign appears three months after move-in. Some contractors make you chase them. The Garrison Standard says the price was in writing and so is the guarantee, and both still mean something after the final invoice.

Common Mistakes to Avoid

• Patching a structural crack without diagnosing it. Joint compound and paint cover the symptom, not the cause. If the crack is movement-related, it returns wider, and you’ve lost the early-intervention window.
• Ignoring a musty odor because it comes and goes. The odor goes when the wall cavity dries and returns when moisture reintroduces. Mold doesn’t leave because you stopped smelling it. It goes dormant.
• Assuming a garage-to-ADU conversion carries the same warranty protections as a new build. Conversions carry more unknowns – old slabs, old wiring, old framing. The warranty terms and what’s excluded need to be read carefully.
• Running an electrical circuit on a breaker that trips occasionally. Repeated tripping is the system telling you it’s protecting itself. Resetting and continuing is how small faults become fires.
• Not documenting the first appearance of a warning sign. Contractors and inspectors respond to evidence, not memory. Photos and dated notes change the conversation.
• Choosing a builder based on a single bid without comparing scope. A low price that excludes a soils report, proper waterproofing, or separate GFCI circuits is not a low price. It’s a deferred cost with interest.
• Waiting until the rainy season to investigate a moisture issue you noticed in September. By the time San Diego’s winter rains arrive, that small window leak has been working for four more months.

When to Call a Professional

Some warning signs are informational – you document them and keep an eye on them. Others demand a professional the same week you spot them. Call a licensed contractor when a crack exceeds 1/16 inch and shows diagonal pattern, when a musty odor persists after two days of ventilation, when a breaker trips twice within a week under normal load, or when a mini-split is dripping water inside the living space. Also call if your ADU is still inside its warranty period and you’ve documented a defect – most warranties have a claims window, and waiting expires it. Fielding ADU San Diego offers free estimates throughout San Diego – call (858) 264-3027 and someone will pick up. A live person, every time, whether it’s noon or midnight.

Frequently Asked Questions

The Bottom Line

ADU warning signs in San Diego follow patterns, and patterns are learnable. A 45-degree crack from a door corner, a musty smell at the garage wall, a breaker that trips on a Tuesday, a mini-split that drips water down your living room wall – these are all messages the building is sending. Read them early and the fix is manageable. Ignore them and the same message arrives a year later as a five-figure repair. Document what you see, know what your warranty covers, and when the sign says structural, don’t guess. For ongoing maintenance tips, see our more guides & resources. Call someone who prices in writing and stands behind the work for a year. That’s what we do, and we’ve been doing it in San Diego since 2006.

Written by Reed Calloway, Owner at Fielding ADU San Diego, serving San Diego since 2006.