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Boral Home Additions & ADU: The San Francisco Owner’s Guide
If you’re planning a Boral home addition or ADU in San Francisco, the installed cost typically runs between $53,100 and $153,400 depending on square footage, foundation work, and finish level. We stock Boral-compatible trim, siding, and exterior materials in our San Francisco Bay Area warehouse, and we can usually schedule a site walk within the week. What we hear most often from owners is that their existing Boral trim has started to swell at the joints or pull away from the framing, a sign that moisture has found its way behind the pieces and the connection points are failing.
Boral exterior products have a strong track record in California’s coastal climate, but San Francisco’s wet winters and salt air in neighborhoods like the Outer Sunset and the Richmond District put real stress on trim boards, fascia, and soffit edges. When those Boral pieces fail, they need to be matched correctly or the repair sticks out visually and fails again. You’ll find the specifics below, along with what we stock, what a replacement actually costs here, and how we handle the work so the rest of your house stays clean while it’s being done.
Which Boral Models This Applies To
Boral manufactures exterior trim and siding products under several product lines, and the compatibility details matter more than most homeowners realize. The Truexterior line is a poly-ash product with specific dimensions and a shiplap edge profile that is not interchangeable with the TruExterior stone-coated products or the older Boral DuraPanel sheet goods. If your San Francisco addition or ADU was built in the last 10 to 15 years, chances are the trim is Truexterior in 5/4″ nominal thickness boards, but we have seen jobs in the Mission District and Noe Valley where the original contractor used 4/4″ stock, which changes the reveal and the fastening schedule.
To identify what your job needs, check the back of a removed board or any cut end for a stamped label. Boral stamps the product name and production date on most boards; if the label is gone, a 5/4″ Truexterior board measures 1″ thick after milling, while 4/4″ stock comes in at 3/4″. That quarter-inch difference matters when you’re scribing new trim to old stucco or lap siding.
We install Boral OEM material directly, but we also work with quality aftermarket equivalents for trim profiles that Boral discontinued. For ADU projects in San Francisco where the original Boral corner boards or window surrounds are no longer manufactured, we mill matching profiles from Azek or CertainTeed board stock and prime to match the existing paint line. We’ll tell you which route makes sense for your job before any material is ordered, and we’ll show you the price difference in writing. You should know that Elmstead Remodeling San Francisco is an independent service provider and we are not affiliated with Boral; we carry their material because it holds up well here when installed correctly.
Styles & brands we work with
Signs Your Boral Home Additions & ADU Is Failing
- Cracking or splitting at fastener points. Boral trim expands and contracts with temperature swings, and San Francisco’s fog-cool mornings followed by afternoon sun causes more movement than people expect. When boards are nailed too tightly or the wrong fastener pattern was used, they split at the edges. This is the most common failure we see on additions built 8 to 12 years ago. The fix is replacing the failed board and re-setting adjacent pieces with proper spacing.
- Gapping or separation at scarf joints. A properly joined Boral board shows a tight seam at the 45-degree cut, but when the backing wasn’t flashed correctly, the boards pull apart and moisture gets into the joint. In the Outer Parkside and West Portal neighborhoods, we routinely see joints that opened up 1/8″ or more within a few years. Left alone, the gap channels water behind the siding and into the sheathing.
- Barber-pole blistering or bubbling in the paint line. Unlike cedar or fir, Boral doesn’t rot, but a failed paint bond looks similar. The cause is usually a skipped primer coat or installers who sealed only the face and not the cut ends. Moisture moves through the material, lifts the paint, and creates horizontal striping. We sand, prime the raw surface, and repaint using a two-coat system tested for coastal exposure.
- Sagging soffit or fascia on the addition’s eaves. When Boral soffit panels are installed without adequate ventilation or with the wrong clip spacing, they start to bow between fasteners. This is structurally cosmetic at first, but in San Francisco’s higher wind zones near Twin Peaks and Diamond Heights, sagging soffit can pull loose entirely during a winter storm. Repainting won’t fix the underlying attachment issue.
- Visible dark staining at the bottom of skirt boards or water table trim. This points to water wicking up from grade-level concrete or from a patio that pitches toward the wall. Boral trim can handle intermittent moisture, but constant capillary suction at the cut end leads to staining and, eventually, a soft fastening surface. We re-cut the board end, install a Z-flashing kick-out, and sometimes adjust the grade so water runs away from the addition.
See the difference
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After
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AfterReplacement Cost & What’s Included
Replacing Boral trim, siding, or exterior components on a San Francisco home addition or ADU costs between $53,100 and $153,400 when the project includes structural work, foundation improvements, or a full envelope replacement. A smaller trim-and-siding repair job on one elevation is obviously less, but we quote every project as a line-item price before any work starts, so you see exactly where the dollars go.
- Trim board replacement (single elevation): $6,000 – $14,000 installed
- Soffit and fascia replacement on a 400 – 600 sq ft addition: $8,000 – $18,000 installed
- Full exterior re-clad of a 700 sq ft ADU (Boral siding + trim): $45,000 – $95,000 installed
- New ADU construction with Boral exterior package: $106,200 – $259,600 total project
- Garage conversion with Boral exterior upgrades: $35,400 – $94,400 total project
The range comes from access, scaffold requirements, whether we’re matching existing paint and profiles, and how much underlying framing needs repair once we open the wall. Every Elmstead San Francisco job includes shoe covers and drop cloths on every visit, a written price before we cut anything, a photo of the clean-up before the crew leaves, and our 365-Day Done Right Promise on the completed work. We use Boral OEM material whenever the original profile is still manufactured, and we register the material warranty so it travels with your house records.
DIY or Call Us?
You can safely handle the visual inspection and documentation: take photos of the failed boards from a few angles, check for a Boral stamp on the back of any loose pieces, and use a level to see if adjacent boards have moved. That information helps us quote accurately over the phone and brings the right material to the first site visit. If you have to climb a ladder to get to the damaged trim, stop there and call us.
Replacing Boral trim on a two-story addition in San Francisco means working at height over decks, garden walls, and sometimes congested side yards. The boards are dense and awkward; one slipping board can injure a person below or damage a window. We also run ladders on fog-damp hillside lots in neighborhoods like Bernal Heights and Potrero Hill, where footing is tricky and one wrong angle ruins a day, not just a board. If the job is on the ground floor and you want to pull one board yourself, we’ll still be glad to match the profile and sell you the material, but we’ll also tell you if we’d rather do it once, correctly, for less than a second visit would cost. Call (831) 480-4497 and we’ll walk through what you’re seeing.
FAQs
Boral Truexterior and similar poly-ash products carry a 20-year limited warranty and typically last 25 to 30 years in San Francisco’s coastal conditions when installed with the correct fastener schedule and properly primed cut ends. In areas with heavy fog drip like the Sunset and Lake Merced, the paint line needs maintenance every 7 to 10 years, which is on par with any exterior material in the city.
Small hairline cracks can sometimes be sanded, filled with an approved poly-ash filler, and repainted, but any board with a split running through more than one fastener point should be replaced. Boral doesn’t absorb moisture like wood, so rot repair doesn’t apply; the failure is almost always mechanical. Call (831) 480-4497 if you want us to look at photos and tell you honestly which route we’d take.
A single-elevation trim replacement usually takes 2 to 3 working days, including tear-out, any framing repair, installation, caulking, and first paint coat. Larger projects like a full re-clad of an ADU run 2 to 4 weeks depending on scaffold permits and weather, and we’ll set that schedule in writing before the first truck rolls.
We keep common Boral Truexterior profiles, 5/4″ trim boards, 1x fascia, and corner boards in our San Francisco Bay Area warehouse, along with compatible primers and two-part caulks. Specialty profiles and longer lengths are ordered from regional suppliers and usually arrive within 5 business days. We’ll tell you at the estimate which materials are on hand and which are coming in.
If you have a Boral addition or ADU in San Francisco with failing trim, siding, or soffit work, the next step is a phone call. We’ll ask some questions, ask for a few photos, and give you a written price before anyone steps inside your home. Call (831) 480-4497 for a free estimate, and we’ll work around your family’s schedule, not the other way around.
Written by Graham Stein, Owner, Elmstead Remodeling San Francisco at Elmstead Remodeling San Francisco, serving San Francisco and nearby areas.
