Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Key Largo
Planning a home addition or ADU in Key Largo means dealing with two realities most Florida contractors never face: the Key Largo Limestone bedrock just below the surface, and Monroe County’s strict ROGO permit allocation system. We’ve worked through both for years. A typical home addition in Key Largo runs $45,000 to $130,000, while a full detached ADU starts around $90,000 and can reach $220,000 depending on pilings, elevation, and finishes. Call (877) 610-1318 and we’ll walk the site with you before you spend a dollar on plans.
What makes building here different isn’t a mystery to us. The island’s fossilized coral foundation means standard excavation and footing work won’t happen. Every structure gets driven concrete pilings anchored into bedrock. That’s how it’s done on Key Largo, and that’s how we do it. If you’re a homeowner near the 33037 corridor from the north end around Carysfort down through Rock Harbor and Largo Sound, you already know the ground fights back when you dig. We plan around it from day one, not after the first backhoe strike.
Why Barrett & Sons Construction Is Key Largo’s Preferred Home Additions & ADU Company
Tom Barrett started this company in 1998, and his sons run the crews today. Call us and you’re talking to someone who answers their own phone, not a national call center reading from a script. When we quote a price for a home addition on Key Largo, it comes in writing with a change order before any scope move. The allowance that isn’t on paper is a surprise waiting for a date, and nobody here wants surprises at $45,000 and up.
Key Largo homeowners don’t need a contractor who’s learning Monroe County code on their dime. They need someone who knows that every permitted project in the 33037 ZIP has to pass both the High-Velocity Hurricane Zone wind standards and the flood elevation review, often with a licensed engineer’s certification. We pull permits and schedule inspections on every eligible job because the inspector works for you, not for us. That’s how we’ve built our name from Garden Cove to Upper Key Largo and everywhere between.
And we back the work with a written 90-Day Done Right Promise. If something isn’t right, one call brings Tom back. No arguing, no fine print games. You’ll also find our price honesty written into every contract: written allowances, written change orders, written scope. Background-checked crew members in uniform show up on time, every time. We live by the L.O.C.A.L. code: Local roots, On time, Community first, Accountable, Loyal. Tom publishes his name, address, and license number. Look him up before you sign anything.
If you’re searching for Home Additions & ADU help from a company that treats your file like it’s their own house, you’ve found the right crew. We coordinate from our South FL office and serve Key Largo with scheduled crews who know the island’s building conditions cold.
Our Home Additions & ADU Services in Key Largo
ADU Design & Permitting
Getting an ADU approved in Key Largo means surviving Monroe County’s ROGO allocation system, which caps new construction permits island-wide. The design has to satisfy HVHZ wind codes and FEMA flood elevation requirements at the same time. We handle the plans, the engineer’s certification, the floodplain review, and the permit application so you don’t sit in limbo wondering if your allocation will expire before drawings clear.
Garage Conversion ADU
A garage conversion in Key Largo typically runs $30,000 to $80,000, but the real variable here is what’s under the slab. Many existing garages weren’t built with the continuous load path or flood-elevation compliance a legal ADU needs. We assess the existing pilings and foundation first because converting a garage that can’t support the additional living load is a costly mistake no contractor should let you make. If your garage is on solid driven pilings and has the clear height, this can be the fastest path to income-producing space on the island.
New Detached ADU
Building a detached ADU from the ground up on Key Largo lands you in that $90,000 to $220,000 range. The pilings alone can run tens of thousands depending on your lot’s bedrock depth. We spec stainless steel and hot-dipped galvanized hardware as standard because the permanent salt air off the Atlantic and Florida Bay chews through standard fasteners in years, not decades. A detached ADU here is an investment in rock-solid construction, not a weekend project.
Junior ADU & Interior Conversion
If your Key Largo home has an underused space that’s already inside the footprint, a junior ADU or interior conversion avoids the most expensive site work entirely. We’ve converted stilt-home ground levels, enclosed Florida rooms, and split existing floor plans into self-contained units without driving a single new piling. This route often stays under $45,000 and clears permitting faster because you’re not changing the building envelope.
Many of the same trades that make an ADU feel livable come from our Kitchen Remodeling in Key Largo team, and when the ADU needs a second bath, our Bathroom Remodeling in Key Largo crew handles the wet work under the same roof.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Key Largo
We’re not installing mystery materials off the back of a van. When your Key Largo addition calls for impact-rated windows or doors, we work with PGT, CGI, and Simonton because those are the brands Monroe County inspectors see every week and trust. The salt-heavy air here doesn’t forgive cheap aluminum or substandard glazing. We stock what Key Largo jobs need and order the rest with realistic lead times, not promises we can’t keep. If you want to look up the window series before we install it, go right ahead. We’d rather you verify the spec yourself.
Common Home Additions & ADU Problems We See in Key Largo Homes
- Bedrock that won’t budge: The Key Largo Limestone formation sits anywhere from a few inches to a few feet below grade, which makes conventional trenching impossible. Any addition or ADU here needs driven concrete pilings, and if a contractor shows up talking about digging footings, they don’t know the island.
- ROGO permit limbo: Monroe County’s Rate of Growth Ordinance caps new construction permits. A homeowner who waits too long to lock in their allocation or files incomplete drawings can watch their project stall for a year or more. We file correctly the first time.
- Pre-HVHZ structural gaps: Homes built before the post-Andrew codes often lack the roof-to-wall connections, continuous load paths, and impact-rated openings that a legal addition must tie into. Retrofitting those connections is a routine part of our additions, not an extra surprise fee.
- Salt-air corrosion: Standard anchor bolts and fasteners rust fast between the ocean and the bay. We specify stainless or hot-dipped galvanized hardware as baseline on every Key Largo project, because replacing corroded anchors on a finished addition costs far more than doing it right the first time.
Pricing for Home Additions & ADU in Key Largo, FL
The numbers below are real ranges for this island, not mainland Florida numbers dressed up to look local. A home addition in Key Largo runs $45,000 to $130,000. A new detached ADU runs $90,000 to $220,000. A garage conversion runs $30,000 to $80,000. A junior ADU or interior conversion often stays under $45,000. What moves your price: piling depth to bedrock, HVHZ glazing and opening protection, flood elevation height above grade, and site access. We give free estimates and written line-item quotes. No change order starts without your signature. Call (877) 610-1318 and we’ll put the real number in front of you before you decide anything.
We Also Serve Cities Near Key Largo
While Key Largo is our focus on this page, our crews also run regularly to Florida City, Homestead, Leisure City, and Naranja for homeowners who need the same written-scope, permits-pulled approach without the island commute. You’ll get the same crew, the same standards, and the same fixed pricing. No surprises either side of the Card Sound Bridge.
Serving Key Largo, FL - Our Local Coverage Area
We’re based in the Key Largo area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Home Additions & ADU in Key Largo
Once your ROGO allocation is secured and plans clear Monroe County review, we can typically mobilize within two to four weeks. The variable is almost always the permitting side, not our schedule. Call (877) 610-1318 and we’ll give you a realistic timeline based on where your project sits in the approval queue.
Yes, we service the entire 33037 ZIP, from the northern stretches around Carysfort and the Marina area down through Rock Harbor, Largo Sound, and the residential pockets around John Pennekamp Coral Reef State Park. Our crews know the access constraints on ocean-side and bay-side lots alike.
A detached ADU here runs $90,000 to $220,000, and the premium over mainland pricing comes mostly from driven pilings and the dual flood-and-wind compliance review. On the mainland you might pour a slab and go. Here, bedrock dictates the foundation, and that’s a cost you can’t avoid if you want a legal, insurable structure. We’ll show you exactly where the piling dollars go.
Yes. Every Key Largo project we take on includes the HVHZ wind analysis, flood elevation certification, and Monroe County floodplain review as part of our permitting package. We don’t treat these as extras because on this island they’re the price of a legal build. The engineer’s certification, the elevation survey, and the inspection scheduling are all in our scope.
Every Barrett & Sons job carries our written 90-Day Done Right Promise. If something isn’t done right, Tom comes back and makes it right with one call. Workmanship issues show up in that window, and we handle them without lawyers or runaround. The 90-day promise is written on every contract, not buried in fine print.
Get Your Free Home Addition or ADU Estimate in Key Largo
The ground under Key Largo doesn’t forgive shortcuts, and neither do we. If you’re planning a home addition, garage conversion, or a full detached ADU anywhere in the 33037 ZIP, start with a conversation. Call (877) 610-1318 today. Someone answers the phone, we’ll schedule a site visit, and you’ll get a written estimate with real numbers for Key Largo’s conditions. No trip charge inside the county. No pressure. Just straight answers from a local crew that puts its name on the truck.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Key Largo, FL since 1998.