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Boral Home Additions & ADU: The Miami Owner’s Guide
Boral home additions and ADU construction in Miami runs $53,100 to $153,400 installed, depending on square footage, foundation work, and whether you’re building out or up. We stock Boral-compatible trim, siding, and structural components, and we match existing Boral profiles so the new work blends with what you already have. Most owners call us because a previous addition is showing water damage at the seams, the Boral trim is pulling away from the wall, or they’ve been quoted a number by a builder who never mentioned that Miami-Dade wind-load codes would add $8,000 to the final bill.
One thing to know before you start: “home addition” and “ADU” are not the same job in Miami. An addition attaches to your existing house and shares its systems. An ADU (accessory dwelling unit) is a separate living space with its own kitchen, bath, and entrance, and it triggers a different set of permitting, setback, and impact-fee requirements. Neither is a small job, and both deserve a written price before anyone swings a hammer.
Key Takeaways:
- Installed cost for a Boral home addition in Miami: $53,100 – $153,400; standalone ADU construction runs higher at $106,200 – $259,600.
- Boral trim and siding are engineered for moisture resistance, but South Florida humidity and salt air shorten the lifespan compared to drier climates.
- Miami-Dade County requires HVHZ (High Velocity Hurricane Zone) rated materials on most addition work. Not every Boral profile meets that spec on its own.
- We deliver a written price before any work starts, backed by our 365-Day Done Right Promise.
Which Boral Models This Applies To
Boral manufactures several product lines that show up in Miami additions and ADUs. The most common we work with are Boral TruExterior trim and siding, Boral Versetta Stone (a stone-look siding panel), and BoralTruexterior fascia boards. If your existing addition used Boral trim, the profile is usually marked on the back of the board or on the original invoice, but here’s the practical reality: after a few South Florida summers, the printed markings fade or get painted over.
The smarter way to identify what you have is to measure the reveal and thickness. Boral trim boards typically run 5/4-inch thick (actual measurement 1 inch) in widths of 4, 6, 8, 10, and 12 inches. TruExterior siding comes in 16-foot lengths but is commonly cut into 12-foot sticks for Miami jobs because a 16-foot board is hard to transport through tight neighborhood turn-ins. If your trim is pulling away and exposing a foam core, it’s likely not Boral, because Boral is solid-cell PVC with no foam backing. That matters because the replacement needs to match the original’s expansion and contraction rate.
For the OEM-versus-aftermarket decision: Boral has discontinued some profiles over the years, and when a matching profile is no longer made, we use a code-compliant PVC or fiber-cement equivalent that matches the reveal and finish. We’ll tell you if we’re substituting and why. We’re an independent contractor, not affiliated with Boral, so our recommendation is based on what works, not what one manufacturer wants us to push.
Styles & brands we work with
Signs Your Boral Home Additions & ADU Is Failing
- Caulk joints cracking repeatedly around Boral trim. Boral expands and contracts with temperature swings, and Miami’s daily heat cycle is brutal. If the original installer nailed instead of screwed the trim, the boards will work loose and crack the caulk within a season or two.
- Water stains on interior drywall near the addition’s roofline. This usually traces back to flashing that wasn’t lapped correctly where the new roof ties into the old one. The Boral trim is rarely the actual leak source; it’s the transition.
- Boral siding boards bowing or cupping on the south and west exposures. Direct Miami sun heats dark-colored siding well past 150°F. If the boards were installed without proper spacing for expansion, they’ll warp and the fasteners will pull through.
- Gaps opening where the addition meets the original house. Two structures settle at different rates in Miami’s sandy soil. When the gap widens past about 3/8 of an inch, you’re looking at either a foundation issue or a missing expansion joint.
- Musty smell inside the ADU or addition after heavy rain. Miami gets 60-plus inches of rain a year, and if the Boral siding’s weep holes are blocked or missing, trapped moisture rots the framing behind it. By the time you smell it, the framing has been wet for a while.
See the difference
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After
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After
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AfterReplacement Cost & What’s Included
For a Boral-focused home addition or ADU repair and replacement scope in Miami, you’ll see these installed ranges:
| Scope | Installed Price Range |
|---|---|
| Full home addition (new build-out, Boral trim and siding) | $53,100 – $153,400 |
| ADU construction (standalone unit, Boral exterior package) | $106,200 – $259,600 |
| Garage conversion using existing slab | $35,400 – $94,400 |
| Boral trim replacement (exterior, partial, 200 – 400 linear feet) | $4,130 – $10,620 |
What drives the spread on an addition: foundation type (Miami’s water table means many additions need helical piers or significant fill, and that’s a five-figure line item before framing starts), whether the roof ties into the existing roof or stands alone, and how much of the mechanical load your panel can handle. On ADUs, the biggest variable is bringing sewer and electric from the street to a back-lot structure that was never plumbed for one.
Every quote we write includes parts, labor, fasteners, flashing, permit-related inspections, and our written warranty. You’ll get one number before we start, and that number does not move unless you change the scope. Our 365-Day Done Right Promise states it plainly: if it’s not right within a year of completion, we return and fix it at no cost to you.
DIY or Call Us?
You can safely check a few things yourself. Confirm whether the failing material is actually Boral (look for solid PVC edges, not foam). Check for blocked weep holes along the bottom of siding runs. Inspect where the addition’s roof meets the main house for loose or missing flashing. That’s the diagnostic work an owner can do with a ladder and a good flashlight.
What you shouldn’t do is start pulling Boral trim boards off your house. Removing one board usually disturbs the ones flanking it, and if the water barrier underneath is compromised, you’ve just opened a path for the next Miami downpour to get behind your siding. When framing, flashing, or structural connections are involved, the risk of a small mistake compounding into a five-figure repair is real. If the problem is anything beyond a single caulk joint, call (850) 780-8123 and tell us what you’re seeing. We’ll give you a straight answer about whether it needs a pro.
FAQs
Boral trim is engineered to last 25 to 30 years in most climates, but Miami’s combination of UV exposure, salt air, and humidity typically brings that down to 15 to 20 years before you’ll see meaningful deterioration at the joints and fasteners. Proper installation with the right spacing and stainless or ceramic-coated fasteners extends that significantly. Call (850) 780-8123 for an assessment of your specific exposure.
Yes, in roughly 60 percent of cases we see, the failure is at the flashing, caulk, or fastener level, and those can be repaired without tearing down the addition. The deciding factor is whether the water has reached the framing. We’ll open a small inspection point, look at the sheathing, and tell you what’s actually needed before quoting anything.
A partial trim and siding repair runs 3 to 7 working days. A full addition typically takes 8 to 16 weeks depending on permitting, foundation work, and roof tie-in complexity. An ADU runs 4 to 9 months because it requires separate utility runs and its own permitting path through Miami-Dade. We give you a schedule in writing with the price, and we hold to it.
We stock Boral TruExterior trim boards in the most common Miami widths (4, 6, 8, and 12 inch) and we carry Versetta Stone samples and panels at our shop. Discontinued Boral profiles take 1 to 2 weeks to source from remaining distributor inventory. We also stock compatible parts for KraftMaid, Cambria, and Silestone projects. Call (850) 780-8123 and tell us your Boral profile and measurements; we’ll confirm stock before you schedule anything.
Call Mason Remodeling Co Miami at (850) 780-8123 for a free estimate on your Boral addition or ADU work in Miami. A live person answers every call, any hour, any day. We’ll put a written price in your hands before any work begins, and we’ll stand behind it for 365 days after completion.
Written by Isaac Pruett, Owner, Mason Remodeling Co Miami at Mason Remodeling Co Miami, serving Miami and nearby areas.
