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Oldcastle Home Additions & ADU: The Fort Lauderdale Owner’s Guide
Home additions and ADU construction in Fort Lauderdale typically run $45,000 to $130,000 for a full addition, with detached ADUs landing between $90,000 and $220,000 depending on size, permitting, and foundation work. Most Fort Lauderdale homeowners call us when they see water staining at the tie-in seam between the original structure and the addition, or when the ADU’s subfloor starts feeling spongy near the exterior walls. Those are usually framing or flashing failures from the original build, not cosmetic issues, and they get worse fast in South Florida humidity. Isaac Pruett has spent almost twenty years running additions in Fort Lauderdale, and the failed part is rarely the pretty stuff you can see.
Mason Remodeling Co Fort Lauderdale is an independent service provider, not affiliated with Oldcastle. We work with Oldcastle-compatible framing members, sheathing, and foundation components on every addition and ADU we build or repair.
Which Oldcastle Models This Applies To
Oldcastle home addition and ADU components fall into a few distinct categories, and getting the right match matters more than most people expect. The biggest compatibility gotcha we see in Fort Lauderdale involves Oldcastle concrete masonry units and tie-beam systems: older builds used 8-inch CMU with standard 4-inch knockouts, while newer ADU plans call for 6-inch modular block that does not accept the same anchor bolts or rebar spacing. If you’re pulling dimensions off an existing wall, measure the actual block depth and web spacing before ordering anything.
For sheathing and subfloor, the OEM-versus-aftermarket question usually comes down to exposure rating. Oldcastle-specified engineered panels are treated for South Florida’s moisture levels; generic big-box equivalents often are not, and we have replaced more than a few delaminated subfloors in Victoria Park where someone saved $400 on the wrong panel. We stock Oldcastle-compatible CMU, tie anchors, and pressure-treated sill plates on our trucks, and we verify label codes against your original plans before we start cutting.
Styles & brands we work with
Signs Your Oldcastle Home Additions & ADU Is Failing
- Water staining or efflorescence at the seam where the addition meets the original house. This almost always means the flashing detail failed or was never installed correctly. Water wicks into the CMU, and in Fort Lauderdale’s wet season, that accelerates spalling and anchor corrosion within a couple of years.
- Doors or windows in the addition that suddenly stick or will not latch. That’s movement, not humidity. The foundation or the tie-in has shifted, and the opening is no longer square. Ignoring it means cracked tile and drywall next.
- Spongy or bouncy spots in the ADU floor near exterior walls. Moisture has gotten into the subfloor, usually because the sill plate was not properly isolated from the slab. We find this constantly in garage conversions done on the cheap.
- Vertical cracks in the stucco or drywall at outside corners of the addition. Small settling cracks are normal in year one. Cracks wider than a quarter-inch, or cracks that keep growing, point to a foundation or tie-beam problem that needs a structural look, not caulk.
- Musty smell that will not go away even after deep cleaning. Your nose is usually right. That odor means moisture is trapped in a wall cavity or under the floor, and in Fort Lauderdale’s climate it will not dry out on its own.
See the difference
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AfterReplacement Cost & What’s Included
In Fort Lauderdale, full home additions run $45,000 to $130,000, and ADU construction ranges from $90,000 to $220,000. The spread comes down to three things: whether you’re tying into an existing slab or pouring new footers, how much of the original framing is salvageable, and what the city requires for wind-load ratings on the new structure. Here’s the breakdown:
| Project Scope | Typical Fort Lauderdale Range |
|---|---|
| Garage conversion to living space | $30,000 – $80,000 |
| Full home addition | $45,000 – $130,000 |
| Detached ADU construction | $90,000 – $220,000 |
Every line item is written down before we start. That includes the Oldcastle-compatible materials, labor, permits, and disposal. You get the price in writing, and it does not change unless you change the scope. Our workmanship warranty runs 365 days from the completion date, and if something fails on our watch, we come back and fix it at no charge.
DIY or Call Us?
If you’re dealing with a wet seam or a sticking door, you can safely do some diagnosis: run a hose along the roof tie-in and watch where water travels, or mark crack edges with a pencil and check them weekly. What you should not do is open up a load-bearing wall, jack a sagging beam, or cut into a CMU wall that may be carrying roof load. That is where we see the worst injuries and the most expensive repair bills. A wrong cut into a load-bearing block wall in Fort Lauderdale is not a mistake you can spackle over.
We tell you what we found, what it takes to fix it, and what it will cost, before we touch a thing. If you’re seeing any of the signs above, call us at (754) 354-3720 and we’ll come take a look.
FAQs
A properly built addition using Oldcastle-compatible CMU and correctly flashed tie-ins should last 50 years or more in Fort Lauderdale, though exposed flashing, stucco, and subfloor components typically need attention every 10 to 15 years due to salt air and humidity. Poorly flashed seam work can fail in as little as two to three years. Call (754) 354-3720 if you suspect water intrusion at the tie-in, and we’ll give you an honest assessment.
Most seam and subfloor failures can be repaired without tearing down the whole addition, as long as the CMU block itself is still sound and the foundation has not shifted beyond tolerance. We replace the failed flashing, sill plates, and any rotted sheathing, then re-secure the tie-in to current Fort Lauderdale wind-load code. The free estimate will tell you exactly what needs replacement versus what can be salvaged.
A focused seam repair or subfloor replacement on an Oldcastle-compatible addition usually takes three to seven working days, while a full ADU build or major structural correction runs eight to sixteen weeks depending on permitting and inspection schedules in Fort Lauderdale. We give you a written timeline before work starts, and we call you if anything changes.
We stock Oldcastle-compatible CMU blocks, tie anchors, sill plates, and flashing on our trucks, and we source any specialty panels or engineered components through our supplier network so you never have to chase down parts. We also work with specification-grade brands like KraftMaid, Cambria, and Silestone when interior finishes are part of the job. Call (754) 354-3720 and we’ll verify compatibility against your original plans before we order anything.
Written by Isaac Pruett, Owner, Mason Remodeling Co Fort Lauderdale at Mason Remodeling Co Fort Lauderdale, serving Fort Lauderdale and nearby areas.
