Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Boral Home Additions & ADU: The San Jose Owner’s Guide
We stock and install Boral-compatible home addition and ADU components across San Jose, with typical projects running $53,100 to $153,400 installed. Same-week site visits are standard once we have the written scope locked. Most owners call us after discovering a materials failure mid-project: sheathing that delaminated, flashing that pulled away from the substrate, or a siding profile that no longer matches the original Boral line.
Boral’s exterior products, particularly their siding and trim profiles, show specific failure patterns in San Jose’s dry-summer, wet-winter climate. What fails first is usually the seal point between Boral trim and the adjacent material. Once water gets behind the trim face, the substrate starts moving, and that movement telegraphs through as cracked caulk lines, popped fasteners, or visible gaps at the roofline and window returns. We carry Boral-spec trim, siding, and accessory stock on our trucks for match-out work, and we order full production runs direct when the addition needs to look seamless.
Bradford Remodeling Co San Jose is an independent contractor. We are not affiliated with Boral, and we do not sell their products as a dealer. We install them because the spec sheet is honest, and because homeowners who already have Boral on the house do not want a patch job that reads as a patch job from the street.
Key takeaways:
- Home additions and ADUs in San Jose run $53,100 to $153,400, with the final number driven by foundation type, roof tie-in complexity, and how much existing Boral trim must be matched or replaced.
- The 365-Day Done Right Promise covers every completed addition and ADU component we install. If work fails within the guarantee period, we return and correct it at no charge.
- Written price before any work starts. No numbers that move at the door, no change orders unless the scope changes in writing.
- We stock common Boral profiles for repairs and small match-outs; larger production runs are ordered direct and verified against the original lot where possible.
Which Boral Models This Applies To
Most of the Boral product we match in San Jose is exterior cladding and trim, and the compatibility issue is always series-specific. Boral’s siding and trim profiles have changed over the years, and the dimension, reveal, and finish texture vary by production era. The first thing we do on a match-out is pull a clean sample from the existing structure and measure the actual profile, not the nominal spec. A trim board listed as a 1×6 may measure 5/8 inch thick in one production run and 3/4 inch in another. If you hang the wrong stock next to the original, the shadow line tells everyone where the addition starts.
For ADU projects, the Boral question usually centers on exterior compatibility with the primary residence. The city of San Jose reviews ADU elevations against the existing structure for neighborhood compatibility, which means the siding, trim, and soffit detail need to read as the same house, not a second house in the same yard. We document the existing Boral profiles, confirm current production availability, and write the material spec into the permit drawings. The OEM-vs-aftermarket decision is simpler with Boral than with some other brands: the aftermarket options for their trim profiles are limited, and the dimensional tolerance on generics is often too loose for a clean match. We install Boral-spec product when the job calls for it, and we tell you in writing when a quality generic will perform and look correct.
Styles & brands we work with
Signs Your Boral Home Additions & ADU Is Failing
- Caulk line separation at trim-to-siding junctions. This is the early warning. In San Jose’s summer, Boral trim expands in the heat; in winter, it contracts with the cold and moisture. The movement is small but consistent, and caulk is the first thing to let go. When the bead cracks, water gets behind the trim face.
- Visible fastener heads with rust halos. If the original installation used standard fasteners instead of corrosion-resistant ones, the fastener rusts and stains the surrounding material. More importantly, the rust expands and can spall the edge of the Boral board.
- Bulging or wavy trim runs at the roofline. This means moisture reached the substrate and it is swelling. Boral trim itself does not absorb water, but the framing behind it does. Once the substrate moves, the trim follows, and you get that long, uneven line along the eave.
- Crumbling corners on exposed trim ends. Boral is cementitious and brittle. Repeated impact, overdriven fasteners, or simple freeze-thaw cycling at a butt joint can cause the corner to blow out. It starts as a small chip and worsens with each rain cycle.
- Gaps opening at window and door returns. When the addition or ADU is framed tight against the primary structure, differential settling moves the two structures at different rates. The gap that opens at a window return is the structure telling you the trim was over-constrained.
See the difference
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After
Before
After
Before
AfterReplacement Cost & What’s Included
For a full home addition or ADU in San Jose, the $53,100 to $153,400 range covers the complete project, not just the Boral components. On a smaller scale, if you need us to match and replace a failing Boral trim run on an existing addition, the work is priced by the linear foot and the complexity of the access. We give you a written line-item price, parts plus labor, before we start. No allowances that balloon later.
What drives the range on a larger project: foundation type (slab versus raised), the roof tie-in detail, whether the city requires fire-rated exterior assemblies, and how much existing Boral must be matched versus replaced. When we write the number, we also write the scope, and we sign both. That is The Garrison Standard. Every project we complete carries the 365-Day Done Right Promise: if the work fails within a year under normal use, we come back and correct it at no charge. You will have it in writing.
DIY or Call Us?
You can safely check your own Boral trim for the warning signs above: caulk separation, rust halos, bulging runs, chipped corners, and window-return gaps. None of that requires a ladder. What you should not do is attempt to pull and reset Boral trim yourself. The product is heavy, brittle, and unforgiving when improperly fastened. A homeowner prying a trim board off a second-story eave with a flat bar is how falls and broken material both happen.
If the failing piece is at ground level, on a single-story wall, and you know what you are doing, a careful patch is possible with the right stock and pre-drilled fasteners. If the issue involves scaffolding, roof-tie flashings, or anything structural, call us at (669) 272-2637. We will come look at it, write the number, and do it by the book.
FAQs
Boral’s cementitious exterior products carry a manufacturer’s warranty that typically extends to 50 years in this climate, but the real-world failure point in San Jose is the installation, not the material. Properly installed with corrosion-resistant fasteners, correct edge clearances, and compatible flashing, Boral trim should outlast the caulk joints at least two to three times before any repair is needed.
Yes, if the damage is localized and the surrounding board is sound. A chipped corner can be patched with a cementitious repair compound and painted to match, and a separated caulk joint can be cleaned and re-sealed. But if the substrate behind the trim is swollen or the trim itself is cracked through, replacement is the honest fix. We will tell you which one applies and write the price for that, not a worse-case scenario. Call (669) 272-2637 to schedule a look.
Typical single-wall trim replacement takes one to two days once the materials are on site. If we are matching a profile that is no longer in production, add a week for us to source the closest current stock and verify the dimensions against your sample. Full addition and ADU projects run on their own schedule, written clearly in the contract scope.
We stock common Boral trim profiles, along with compatible flashings, sealants, and corrosion-resistant fasteners, on our service trucks for match-outs and repairs. For full production runs on a new addition or ADU, we order direct and confirm the product against the existing install before any of it goes on the wall.
If you have failing Boral trim, a match-out problem, or you are planning an addition or ADU in San Jose and want the exterior done right, call (669) 272-2637. We will write the number, put the scope in your hand, and stand behind the work for a full year. Straight number, written scope, done when we said done.
Written by Curtis Lane, Owner, Bradford Remodeling Co at Bradford Remodeling Co San Jose, serving San Jose and nearby areas.
