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Boral Home Additions & ADU: The San Diego Owner’s Guide
Adding square footage with a Boral-accented home addition or ADU in San Diego typically runs $53,100 – $153,400 for the full project, depending on whether you’re framing a single room bump-out or a permit-heavy detached accessory dwelling unit with kitchen and bath. Most owners call us after they’ve lived with the idea long enough to need a real number, not after something physically broke. That’s the odd thing about additions and ADUs as a “part” category: the failure is usually in the planning phase, not the framing.
That said, there are component failures we see on existing Boral-trimmed additions across San Diego: cracked trim boards where stucco meets fascia, failed flashing at the roof-to-wall intersection, and ADU door thresholds that leak during our winter rain. If you’re reading this because something on your existing addition is failing, the fix usually lands between $470 and $2,950. If you’re reading because you want to build, the number is bigger and we’ll show you exactly how we get there.
Which Boral Models This Applies To
Boral doesn’t manufacture room additions, but their exterior trim, siding, and fascia products wrap a lot of San Diego additions and ADUs. The compatibility question is usually about the Boral TruExterior line: poly-ash trim boards in 5/4 and 4/4 thicknesses, siding profiles ranging from nickel-gap to shiplap, and corner boards that run 1×4 through 1×12. TruExterior is the product we see most often on additions in neighborhoods like Clairemont, North Park, and University Heights.
There’s a real compatibility gotcha here: Boral TruExterior cuts and mills differently than fiber cement. It’s lighter, it doesn’t hold a routed profile the same way without finish sanding, and it expands and contracts far less than wood or PVC. If a previous contractor mixed TruExterior trim with off-brand poly-ash or fiber cement, the joints open up over time because the thermal movement rates don’t match. We check that when we inspect an existing addition. For replacements, we recommend staying within TruExterior for any board abutting original Boral material. Quality aftermarket equivalents exist, but the marginal savings disappears the first time a mismatched joint cracks under San Diego’s sun-and-marine-air cycle.
Penhallow Remodeling San Diego is an independent contractor and not affiliated with Boral. We stock TruExterior trim profiles on our trucks alongside our other trade brands: KraftMaid, Cambria, and Silestone for interiors.
Styles & brands we work with
Signs Your Boral Home Addition or ADU Component Is Failing
- Paint peeling at the bottom edge of trim boards. Water wicks up through end grain where a board meets concrete. Once the bottom edge swells, the paint bond fails and the board starts holding moisture.
- Gaps opening at outside corners. San Diego’s daily thermal swing is modest, but marine air and direct afternoon sun work corners hard. A gap wider than 1/16 inch means the fasteners have loosened or the board was under-sized at install.
- Soft spots on fascia or window trim. Press with a thumb near any joint or fastener. If it gives, dry rot has started. TruExterior resists rot far better than wood, but incorrectly flashed seams let water sit behind it anyway.
- Doors or windows that have been fine for years but now stick. On additions built over crawlspaces, settlement or shifting pier blocks throw the rough openings out of square. The Boral trim around those openings is often the first thing to show stress at the mitered corners.
- Visible rust stains below trim seams. If a previous contractor used uncoated fasteners on TruExterior, the tannins in the poly-ash react and bleed. It’s mostly cosmetic, but it tells you the fasteners are corroding and should be swapped before one lets go.
See the difference
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AfterReplacement Cost & What’s Included
What you’ll pay to fix a failing Boral component on an existing addition or ADU in San Diego depends on how far the damage runs. Repairing flashing at a single roof-to-wall junction typically runs $470 – $1,400. Replacing a full run of fascia around an ADU roofline runs $1,200 – $2,950. We write the number before we start and it doesn’t change unless we find rot behind the trim that nobody could see until it was opened up. If we find that, we stop, show you photos, and give you a new written price before we proceed.
When we quote, you get three lines you can hold us to: parts, labor, and haul-away. No supply-chain upcharges, no surprise “trip fee,” no revision at the door. And every repair carries our 365-Day Done Right Promise: if the board cracks, the joint opens, or the flashing leaks within a year of our work, we come back and fix it at no charge. That’s in writing, on every project we touch, the same way we’ve operated under the Kingswell standard since 2004.
DIY or Call Us?
If you want to identify what’s failing, you can check for soft spots, open joints, and rust stains on your own. You can also pop off a piece of peeling paint to see whether the substrate under it is solid or spongy. That’s worth knowing before you call, because it tells us whether we’re looking at a trim replacement or something deeper.
But replacing Boral TruExterior trim on a two-story addition means working off ladders or scaffolding, pulling fasteners, cutting boards to match existing profiles, and re-flashing the seams correctly. If it’s done wrong, water gets behind the new trim and the same failure comes back in two years. We’d rather you not learn that lesson twice. Call us at (619) 604-9624, tell us what you’re seeing, and we’ll give you a straight answer over the phone before we ever schedule a visit.
FAQs
Boral TruExterior trim typically lasts 25 – 30 years on San Diego additions when installed with proper flashing and coated fasteners, thanks to the poly-ash material’s rot resistance. That’s a conservative number for our coastal climate, where marine air and afternoon sun age most building materials faster. If you’re seeing failures at 10 – 15 years, it’s usually an installation issue, not a material issue. Call (619) 604-9624 and we can tell you which one you’re looking at.
We can repair small areas of Boral TruExterior damage with epoxy patch and repaint if the rot hasn’t compromised the board’s structure and the damage is isolated. Anything wider than a screw head or deep enough to expose fasteners usually calls for a board replacement. The repair route is cheaper today but shorter-lived; we’ll quote both and let you decide with real numbers. Estimates are always free.
A typical single-story ADU trim replacement in San Diego takes one to two days, including haul-away and cleanup. Two-story work or jobs where we’re matching custom milled profiles can add a day. You’ll know the exact window before we start, and we show up inside that window, not a four-hour range that turns into “sometime next week.”
We stock common TruExterior profiles, corner boards, and trim stock on our trucks in San Diego, along with the coated fasteners and flashing materials we use on every installation. Specialty profiles or larger siding runs require a supply house run, which we factor into the schedule ahead of time, not the morning of the job.
Tell me what you need, I’ll tell you what it costs, and we’ll go from there. Call (619) 604-9624 for a free estimate on your Boral home addition or ADU work, and we’ll walk through the options honestly.
Written by Trevor Nash, Owner, Penhallow Remodeling San Diego at Penhallow Remodeling San Diego, serving San Diego and nearby areas.
