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Boral Home Additions & ADU: The Los Angeles Owner’s Guide
If you’re searching for Boral home additions or an ADU in Los Angeles, the short answer is this: we plan, permit, and build additions and accessory dwelling units that integrate with Boral siding, trim, and exterior materials on homes across Los Angeles. A full home addition in Los Angeles typically runs $53,100 – $153,400, while a detached ADU lands between $106,200 and $259,600 depending on size, foundation work, and utility runs. Most owners reach out after noticing exterior Boral trim pulling away from a wall, cracking at the corners, or showing water staining around window surrounds – signs the existing envelope is failing and the structure needs attention before any addition work begins.
What you’re really looking at is a construction project, not a part replacement. Boral’s building products – the siding boards, trim, fascia, and soffit – are part of a larger add-on or conversion project. When we say “Boral home additions” in Los Angeles, we mean additions and ADUs that match or replace your existing Boral exterior system so the new square footage doesn’t look tacked on.
We’re an independent Los Angeles general contractor. Mason Remodeling Co Los Angeles is not affiliated with Boral, but we’ve worked with Boral trim and siding products on additions, garage conversions, and ADUs across this city for years. We know how the material behaves in our dry heat, our wet winters, and our occasional Santa Ana wind events.
Which Boral Models This Applies To
Boral doesn’t make “home addition” components the way a manufacturer makes a furnace or a water heater. What Boral makes – what you have on your house right now – is an exterior cladding and trim system. The main product lines we work with on Los Angeles additions are Boral TruExterior trim and siding, Boral Versetta Stone, and the older Boral Horizon or CedarGrain profiles on homes built in the 1990s and 2000s.
Here’s the compatibility gotcha that trips up Los Angeles homeowners: Boral TruExterior comes in specific profile dimensions, and you cannot substitute a board from another manufacturer without ending up with visible seams, uneven reveals, and a mismatched paint line. TruExterior 5/4 trim boards are actually 1″ thick, not the 1¼” you’d expect from the name. If you’re matching a 7/8″ lap siding reveal, you have to order the same reveal, not a “close enough” size. We measure every existing profile on-site before we price the addition.
For the OEM-vs-aftermarket decision: we recommend genuine Boral material for any visible exterior trim on a Los Angeles addition. Aftermarket composite boards often use different polymer blends that expand and contract at different rates, which shows up as caulking failures at corners within two years. In a city where a 40-degree overnight-to-midday swing is normal in spring, that matters. If the addition is being covered by stucco and the Boral material is only temporary bracing or sub-fascia, a quality aftermarket board can work at a lower cost. We’ll tell you which applies to your project.
Styles & brands we work with
Signs Your Boral Home Additions & ADU Is Failing
These are the symptoms we hear about most often from Los Angeles homeowners calling about additions and ADUs tied to Boral exterior products:
- Caulk separation at trim joints and window surrounds. Boral TruExterior is dimensionally stable, but the caulk sealing it to your stucco or siding isn’t. When you see gaps opening up along the top of a window trim board in Los Angeles, water is getting behind the board. That’s the start of rot in the house wrap, not the Boral itself.
- Warped or buckled siding boards after rain. Older Boral Horizon siding on homes in neighborhoods like Van Nuys or West Adams can absorb moisture if the factory coating was scratched during installation. A board that looked fine in July bucks out of plane after January rain. It’s a material failure, not an installation failure.
- Brittle cracking at exposed end cuts. Boral composite boards should not crack like wood. If you’re finding splits at the bottom edges near grade or around sprinkler overspray, the UV coating has failed and the board’s core is degrading. This is common on south-facing Los Angeles walls with direct sun.
- Water staining on interior drywall near corners. If you see brown water marks inside your home where an exterior corner meets an existing wall, the flashing is compromised. The Boral trim may look fine from the outside. The leak is running behind the board and down the framing.
- Soffit or fascia pulling away from the roofline. In Los Angeles, this often shows up on homes in the hills, where persistent wind and afternoon heat cycles work nails loose. When fascia drops, the gutter system loses support and water starts cascading down the wall.
See the difference
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AfterReplacement Cost & What’s Included
Let’s get to the number you actually want. For a home addition in Los Angeles, plan on $53,100 – $153,400. That covers design, structural engineering, city permitting, foundation work, framing, roofing, plumbing and electrical runs, insulation, drywall, paint, and the Boral exterior trim and siding matched to your existing home. A detached ADU runs $106,200 – $259,600 because you’re building a complete independent dwelling – separate power panel, separate water heater, separate sewer line if the lot requires it.
What drives the wide range is not the Boral material itself. It’s the site conditions and scope: a one-story bump-out on a flat Los Angeles lot costs less than a two-story addition on a hillside with foundation drilling, retaining wall work, and access complications. Garage conversions sit at $35,400 – $94,400 if your existing slab and framing pass inspection.
You get a written price before any work starts. Not an estimate. A price. It itemizes materials, labor, permits, and the Boral trim package. If we discover something unexpected during demolition, you get a written change order before we keep going. That’s our standard on every Los Angeles project, and it’s never waived.
Every addition and ADU we build is covered by the 365-Day Done Right Promise: if the work isn’t right within a year of completion, we make it right at no cost to you. Terms are stated in writing, including what’s covered and for how long.
DIY or Call Us?
You can absolutely walk your own property and identify the failing Boral boards before anyone shows up. Look for the caulk gaps, the cracks, the water staining. Take photos. That helps us price the job before we even arrive.
But a home addition or ADU is not a DIY project, and the structural parts of this work – cutting into load-bearing walls, running new electrical, tying new rooflines into old ones – are genuinely dangerous when handled by someone without framing and trade experience. No one should be working on a live electrical panel or cutting roof trusses without training and permits. Los Angeles has strict building codes, and the city’s Department of Building and Safety will flag unpermitted work when you try to sell. Permits matter.
What you can do safely is document the exterior damage and call us at (213) 632-5711. Isaac Pruett walks every new addition site personally before we price the work. Know who’s coming, know what it costs, know it’s guaranteed – everything else is just noise.
FAQs
Boral TruExterior products carry a 20-year limited warranty from the manufacturer, and in Los Angeles conditions – low humidity, high UV, occasional salt air near the coast – properly installed and painted Boral trim typically lasts 20 to 30 years before paint failure forces a labor-intensive refinish. The bigger failure point in Los Angeles is installation: caulking, flashing, and fastener choices fail in 5 to 10 years if done poorly, which is why we match those details carefully on every addition we build. Call (213) 632-5711 and we’ll tell you whether your exterior issue is a material problem or an installation problem.
Yes, in most cases we can carefully remove, save, and re-install existing Boral siding and trim where the new addition ties in, especially if the boards are in good condition and the paint color is still available. The decision comes down to whether the existing boards can be removed without cracking, and whether the new roofline and wall plane actually match the old one. Call (213) 632-5711 for a free estimate, and we’ll walk the tie-in with you before we write the price.
A one-story addition typically takes 4 to 7 months from the day we start demo to final inspection, and a detached ADU usually runs 6 to 10 months depending on utility trenching, foundation type, and how quickly the city processes your permits. Los Angeles plan check and permitting alone can take 2 to 4 months for an ADU depending on the neighborhood overlay and whether a coastal or hillside review is triggered. We handle the permits, and every project passes final inspection before we call it done.
We order Boral material per project, matched to your existing profiles and paint schedule, because every home’s exterior dimensions and reveals are different and there’s no reason to warehouse boards that may sit through a Los Angeles summer in a hot yard and develop handling damage. We do specify Boral on our additions and ADUs, along with KraftMaid, Cambria, and Silestone products when the project includes a kitchen or bath. Call (213) 632-5711 for an exact materials list and timeline for your specific addition.
Written by Isaac Pruett, Owner, Mason Remodeling Co at Mason Remodeling Co Los Angeles, serving Los Angeles and nearby areas.
