What a New Detached ADU Costs and Involves in Miami
A new detached ADU in Miami typically runs $90,000-$220,000 and takes 6-10 months from permit submission to final inspection, depending on whether you choose prefab delivery or stick-built construction. You’ll need Miami-Dade County permits, a foundation engineered for our shallow water table, and hurricane-rated materials that pass the county’s separate NOA approval system. Call (844) 665-0162 and we’ll walk through your lot conditions and design goals on a free site visit.
How We Build a New Detached ADU in Miami
We’ve learned that homeowners stay sane when they know exactly what’s coming. Here’s the actual sequence we follow on every new detached ADU in Miami, with the decisions you’ll need to make at each stage.
Stage 1: Site Evaluation and Feasibility (Week 1-2)
We walk your property with a surveyor to confirm setback lines, check for overhead utility conflicts, and test soil drainage. Miami’s porous limestone means water can sit just 18 inches below grade in some Coconut Grove and Coral Gables lots, so we decide now whether the foundation needs a raised stem wall or specialized waterproofing. You’ll choose between prefab delivery (faster, tighter cost control) or stick-built (fully custom, longer timeline) before we move to drawings.
Stage 2: Design and Permitting (Week 3-10)
Our architect drafts plans to Miami-Dade’s wind-load and impact-resistant standards. Every window, door, roofing assembly, and structural fastener must carry a Miami-Dade Notice of Acceptance (NOA), not just Florida statewide approval. This is where out-of-county contractors get tripped up, and where our sourcing relationships matter. You’ll finalize square footage (typically 400-800 sq ft for detached units here), ceiling height, and whether you’re adding a kitchenette or full second bathroom.
Stage 3: Foundation and Utility Rough-In (Week 11-16)
We pour a monolithic slab with integrated moisture barrier, or build a raised foundation if hydrostatic pressure demands it. Concurrently, we trench for sewer, water, and electrical tie-ins to your main house. In Allapattah and Brownsville, we’ve found original 1940s-1970s CBS mains that can’t handle the additional load without upgrading the service panel. You’ll need to decide on that upgrade now, not later.
Stage 4: Structure and Envelope (Week 17-24)
Prefab units arrive by crane or modular truck; stick-built crews frame walls with pressure-treated lumber and Miami-Dade-approved fasteners. We install impact-rated windows and doors, then the roofing assembly. You’ll select interior finishes during this stage, kitchen and bathroom fixtures included. We keep samples of Silestone and Caesarstone quartz on-site for countertop decisions, and Kohler and Moen fixtures for wet-area hardware.
Stage 5: Interior Finish and Final Inspection (Week 25-32)
Drywall, flooring, cabinetry, trim, and paint. Miami-Dade inspectors verify egress, fire separation, and utility connections before issuing certificate of occupancy. We do a punch walk with you, then hand over keys and warranty documentation.
The Build Choices That Actually Matter for Your New Detached ADU
Every decision below moves your final number and how the space lives. We lay out the honest trade-offs so you’re not guessing.
- Prefab vs. stick-built: Prefab from partners like Abodu, Dvele, or Mighty Buildings cuts site time by 60% and locks your price early, but limits layout customization. Stick-built gives you any floor plan and material combination, though weather delays and lumber volatility add risk. Most Miami homeowners on tight lots choose prefab; those matching an existing CBS home aesthetic go stick-built.
- Foundation type: A standard monolithic slab runs $8,000-$15,000. A raised stem wall with integrated drainage, necessary where the water table sits high, adds $4,000-$8,000 but prevents the moisture intrusion we’ve seen destroy interior finishes in Allapattah within two years.
- Window and door grade: Miami-Dade requires impact-rated products, but there’s a spread. Vinyl-frame impact windows from PGT or CGI cost less and perform well; aluminum-clad architectural grades from Andersen or Pella cost more but match mid-century modern homes in Coral Gables. You’ll see the difference in your cooling bills and resale value.
- Kitchenette vs. full kitchen: A wet bar with mini-fridge and microwave keeps the unit under 200 sq ft of conditioned space for simpler permitting. A full kitchen with range, dishwasher, and garbage disposal requires grease-trap planning and larger electrical service, but rents for 40% more on the Miami short-term market.
- Utility connection strategy: Tapping existing house sewer and electrical is cheapest when the main panel has capacity. A separate meter and sewer lateral adds $6,000-$12,000 upfront, but lets you rent the ADU as a fully independent unit, which Miami’s zoning increasingly favors.
What New Detached ADU Costs in Miami, FL
New detached ADU construction in Miami ranges from $90,000 to $220,000. Where you land depends on five factors we’ve tracked across dozens of local builds.
| Cost Driver | Low-End Scenario | High-End Scenario |
|---|---|---|
| Square footage | 400 sq ft studio | 800 sq ft 1-bedroom + den |
| Foundation conditions | Stable, dry lot | High water table, requiring raised stem wall |
| Utility complexity | Tie into existing house systems | Separate meter, sewer lateral, panel upgrade |
| Construction method | Prefab delivery, limited custom | Stick-built, architectural finishes |
| Interior material grade | Standard LVP flooring, stock cabinetry | Engineered hardwood, custom KraftMaid or Wellborn cabinets, Cambria countertops |
A written estimate from us includes architectural plans, Miami-Dade permit fees, foundation, structure, rough and finish electrical/plumbing, HVAC, insulation, drywall, flooring, cabinetry, countertops, fixtures, paint, and final cleanup. What typically sits outside that number: landscaping restoration, separate utility meter installation, furniture, window treatments, and any required main-house electrical panel upgrade.
Call (844) 665-0162 for an exact quote on your lot. Estimates are free, and we bring sample materials so you can see the difference between grades before you decide.
What Miami Specifically Does to This Job
Miami-Dade County’s Notice of Acceptance system is the single biggest compliance hurdle for new detached ADU projects here, and it’s entirely separate from Florida’s statewide building code. A roofing shingle approved in Fort Lauderdale or Broward County can be code-illegal in Miami, which means every product in your build, from structural screws to impact windows, must carry the right Miami-Dade NOA number. Contractors who work primarily north of the county line routinely fail inspection on this, adding weeks of re-ordering and re-inspection. We source exclusively through Miami-Dade-approved suppliers, and our permit packages include the full NOA documentation packet upfront.
The housing stock we most often work around was built between the 1940s and 1970s, CBS construction with rebar that’s been eating salt air for 60-plus years. In neighborhoods like Allapattah and Brownsville, we’ve opened walls to find rebar reduced to half its original diameter. That doesn’t stop an ADU project, but it means we assess the main house’s structural integrity before we tie in utilities, because a failing main structure can red-tag the entire property.
Then there’s the water. Miami sits on porous Miami Limestone with a water table that can rise to 2 feet below grade during king tides. Conventional below-grade waterproofing, the kind that works in Orlando or Tampa, fails here because hydrostatic pressure comes from below, not just surface flooding. We design foundations for that reality, with integrated drainage planes and, when necessary, raised stem walls that keep the slab above the water line. It’s not optional, and contractors who treat Miami like inland Florida end up with callbacks for mold and floor failure.
Homeowners often pair a new detached ADU with interior work on the main house, and we’re structured for that. Our Home Additions & ADU in Miami crew coordinates directly with our Kitchen Design & Layout in Miami team and our Backsplash, Tile & Flooring in Miami specialists, so you’re not juggling separate contractors for a unified project. As a Home Additions & ADU full-scope partner, we handle every phase, and we build across Miami and the surrounding areas.
Serving Miami, FL - Our Local Coverage Area
We’re based in the Miami area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked - New Detached ADU in Miami
From permit submission to move-in, expect 6-10 months. Prefab units on simple lots hit the shorter end; stick-built projects with utility upgrades or high-water-table foundations run longer. Miami-Dade’s permit review currently takes 8-12 weeks for ADUs, which we’ve baked into that timeline. Call (844) 665-0162 and we’ll give you a realistic schedule for your specific property.
Yes, absolutely. Miami-Dade requires building, electrical, plumbing, and mechanical permits, plus zoning verification that your lot meets setback and coverage requirements. The county’s NOA product approval system adds a layer that doesn’t exist elsewhere in Florida. We handle the entire permit package, including NOA documentation, as part of our standard process.
Sometimes, if your existing systems have unused capacity. Many 1960s-era homes in Coral Gables and Coconut Grove have 100-amp panels and galvanized supply lines that can’t handle an additional dwelling. We assess this in our first site visit and tell you honestly whether a panel upgrade or water-main replacement is necessary before we price the job.
A 400 sq ft prefab studio with minimal kitchenette, tied into existing house utilities, on a stable, dry lot, starts near the bottom of our $90,000-$220,000 range. The fastest way to push costs up is adding square footage, a separate meter, or a raised foundation. We’ll show you exactly where each option lands before you commit.
We warranty our workmanship for one year, and every product we install carries its manufacturer’s warranty, from GAF or CertainTeed roofing to Kohler fixtures to Andersen or Pella window systems. Because we work with name-brand products, not proprietary or no-name materials, those warranties transfer to you and remain valid if you sell the property. Ask us for the specific warranty terms on any product you’re considering.
Ready to Plan Your New Detached ADU in Miami?
Call (844) 665-0162 to schedule a free on-site estimate. Raymond Estevez or a senior project manager will walk your property, assess foundation conditions and utility access, and bring material samples so you can see your options in person. You’ll leave with a written scope and price range, no obligation.
Written by Raymond Estevez, Owner at Groundwork Construction Co., serving Miami since our founding in South Florida.