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Oldcastle Home Additions & ADU: The Fort Lauderdale Owner’s Guide
If you’re researching Oldcastle home additions or an ADU in Fort Lauderdale, the project typically runs $45,000 to $130,000 for a ground-up addition, or $90,000 to $220,000 for a full ADU build, depending on square footage, foundation type, and finish level. We run into this question constantly: an owner bought a property with an existing addition or ADU that used Oldcastle concrete block and is now seeing cracks, moisture intrusion, or settling around the transition where old foundation meets new. Usually the failure isn’t the Oldcastle block itself. It’s the connection points, the flashing, or a foundation issue that was never addressed when the original addition went up.
Penhallow Remodeling Fort Lauderdale is an independent general contractor, not affiliated with Oldcastle. What we do is match the right materials, diagnose what actually failed, and give you a written price before anything gets torn open.
Which Oldcastle Models This Applies To
Oldcastle APG (now part of CRH) produces concrete masonry units under several lines you’ll see all over South Florida: the standard structural CMU block, split-face architectural block, and retaining wall systems like Belgard and Mesa. For home additions and ADUs in Fort Lauderdale, the structural CMU is what matters most. It’s available in 4″, 8″, and 12″ widths, with 8″ being the code-minimum standard for exterior load-bearing walls in Miami-Dade and Broward County wind zones.
The compatibility gotcha most owners miss: if your original home was built before 2002, it may have been framed with 8″ CMU at a different mix ratio than current Oldcastle product. The new block will physically fit, but the mortar match and the wall tie-in require an engineer’s letter for permit approval. We handle that paperwork. We don’t guess at the connection detail. When the wall goes up, it goes up to the plan the city already stamped.
For OEM versus aftermarket: there is no aftermarket Oldcastle block. Oldcastle is the aftermarket, in a sense, against whatever the 1970s builder used. What you’re really choosing is the fill type (standard grout versus low-density cellular concrete for crawl spaces), the tie-down system (Simpson straps versus embedded anchors), and whether the sill plate gets a capillary break. Those decisions matter more in Fort Lauderdale humidity than the block manufacturer does.
Styles & brands we work with
Signs Your Oldcastle Home Additions & ADU Is Failing
- Stair-step cracking along mortar joints at the addition-to-house seam. This is differential settlement. The original structure has finished moving; the addition hasn’t. In Fort Lauderdale’s sandy, saturated soil, we see this settle for 3 to 5 years after construction, especially in neighborhoods near the New River and Sailboat Bend where the water table sits high.
- Efflorescence (white chalky powder) blooming on block faces below the roofline. Water is getting in through a failed flashing detail or a cracked parapet cap. The block acts like a sponge. Left alone in our humidity, you get spalling within a decade and a mold problem inside the wall cavity.
- Doors or windows in the addition binding at the top corner, not the hinge side. The lintel above the opening is undersized or rusting. In coastal Fort Lauderdale air, even galvanized lintels corrode faster than they do 20 miles inland.
- Musty odor that returns within weeks of a heavy rain, not immediately after. This is slow capillary wick through the block, not a roof leak. It takes days for the moisture to travel through 8 inches of CMU. If the smell peaks 48 hours after rain, check the grade outside the addition before you re-tile anything indoors.
- Horizontal crack at mid-wall height on the west-facing side. That’s not settling; that’s thermal expansion with nowhere to go. An unbroken 40-foot CMU wall in direct Fort Lauderdale sun expands and contracts enough over 10 years to crack itself. Control joints should have been cut at 20-foot intervals. Most additions from the 1990s weren’t.
See the difference
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AfterReplacement Cost & What’s Included
In Fort Lauderdale, a full home addition runs $150 to $300 per square foot, which lands most projects between $45,000 and $130,000 depending on whether you’re adding a bedroom-and-bath or a full primary suite. A detached ADU starts higher because you’re building a complete small home: foundation, utility runs, kitchenette, bath, and its own electrical panel. That’s where the $90,000 to $220,000 range comes from.
What actually drives the number up in this market: whether you need pile-supported foundation (common east of US-1 where soil is loose), how far the new build is from your existing sewer lateral, and whether the city requires impact-rated windows. We use the same Oldcastle-compatible CMU on every Fort Lauderdale job; the difference is what’s inside the wall and underneath it.
Every quote from us includes the block, grout, reinforcement, tie-downs, lintels, flashing, sill seal, permit drawings, engineering letter, and the 365-Day Done Right Promise in writing. If something fails inside that year, we come back and fix it. No service call fee, no second invoice.
DIY or Call Us?
Concrete block looks simple to stack, and for a garden wall, maybe it is. For anything with a roof, electrical, plumbing, and a building permit attached to your property record, this is not a weekend job. The danger isn’t just the weight of the block. It’s the connection detail where new wall meets old wall. Get that wrong and you have a structural seam that separates over time, letting Fort Lauderdale’s afternoon thunderstorms pour into your wall cavity.
What you can safely do: check your addition for the failure signs listed above, take photos, and check whether your original permit is on file with Broward County. Then call (754) 551-2922 and we’ll send someone who knows what they’re looking at. The estimate is free, and the price we give you is the price on the invoice. Trevor Nash grew up around construction and learned this trade at LATTC before spending the better part of two decades running crews across South Florida. We’ve built additions near Las Olas and modest ADUs for homeowners in Wilton Manors who just wanted the space done right. Tell me what you need, I’ll tell you what it costs – then we’ll get it done.
FAQs
Structurally, Oldcastle concrete block lasts 75-plus years if the wall is properly flashed, painted or stuccoed, and kept dry. What fails first in Fort Lauderdale is usually the mortar at the roofline, the lintels over openings, or the stucco skin trapping moisture against the block. We see 30-year-old additions with perfectly sound block and failed flashing. The block is rarely the problem; the water management around it is.
In most cases, yes. Settlement cracks can be stitched with epoxy or helical ties, lintels can be replaced without removing the wall above, and flashing can be retrofitted around parapet caps. Full teardown is only warranted when the foundation itself has rotated beyond repair or when termite damage has compromised the sill plate and top plates. Call (754) 551-2922 and we’ll tell you which one you’re looking at.
A permitted addition typically takes 4 to 7 months from permit approval to final inspection in Fort Lauderdale. An ADU runs 6 to 10 months because of the separate utility connections. Permitting through the city varies: plan review at Fort Lauderdale’s Building Services can take 4 to 12 weeks depending on backlog, and we handle that whole process for you.
We order structural CMU, grout, and reinforcement to the exact spec on your approved plans for every Fort Lauderdale project. We also work with trusted material lines like Belgard pavers, KraftMaid cabinetry, Cambria and Silestone countertops when the addition includes a kitchen or bath. Because we’re working from the permit drawings, the count is exact. No short loads, no leftover pallets piled in your driveway for a month.
Written by Trevor Nash, Owner, Penhallow Remodeling Fort Lauderdale at Penhallow Remodeling Fort Lauderdale, serving Fort Lauderdale and nearby areas.
