What ADU Design & Permitting Actually Costs and Takes in Three Oaks, FL
An accessory dwelling unit in our Three Oaks service area typically runs between $45,000 and $130,000 for design, permitting, and construction, with most projects completing in 5 to 9 months from initial survey to final inspection. The timeline splits roughly into 8-12 weeks for design and Lee County permit approval, followed by 3-6 months of site work depending on whether you’re building a detached unit, converting a garage, or adding above an existing structure. Call (844) 638-7249 for a free on-site estimate that breaks down every line item before you commit to anything.
What makes ADU design & permitting different here isn’t just the Florida Building Code. It’s that Three Oaks sits in a county still rebuilding from Hurricane Ian, which rewrote the rulebook on what gets approved and how fast. We’ll walk you through exactly how that changes your project.
What to look for when you’re hiring for ADU design & permitting
Most homeowners start by comparing three things: price, timeline, and whether the contractor has actually permitted an ADU in Lee County before. The first two numbers matter, but the third one is what keeps your project out of permit limbo. Lee County’s building department has been processing a post-Ian surge for over two years now, and plan reviewers are flagging wind-load calculations and roof-to-wall connection details that a contractor who only builds inland wouldn’t think to include. Ask any builder you interview how many Lee County ADU permits they pulled in 2024. If they hesitate, keep looking.
The second thing to look for is whether the designer and builder are the same company. When an architect draws plans and hands them off to a GC who’s never seen the site, you get change orders. When the person designing the unit knows exactly what our crews cost and what the county will reject, the plans land approved the first time. That’s how we structure our home additions & adu work, and it eliminates the finger-pointing between designer and builder that drags projects out.
Third, ask about their structural engineer relationship. Almost every ADU in Three Oaks needs engineered drawings for hurricane tie-downs, slab connections, and impact-rated openings. If the contractor doesn’t have an engineer they work with regularly, you’ll wait weeks just for stamped calcs while your permit sits in a queue.
How we take an ADU from idea to final inspection
The process breaks into five clear stages. Each one has a deliverable, a timeline, and a decision point for you. Nothing is vague because vague is what causes projects to stall.
Stage 1: Site survey and feasibility (1-2 weeks). We send a survey crew to map your property lines, setbacks, easements, and existing utility locations. In Three Oaks, many lots have drainage easements along the rear property line that eat into buildable area. We flag those immediately because they can kill a detached ADU plan before you spend a dime on design. At this stage you’re deciding whether the ADU goes detached, attached, or above the garage. We give you a buildability report with a rough budget range tied to each option.
Stage 2: Schematic design and bid (2-3 weeks). Our designer draws three layout options scaled to your site, each with a different square footage and configuration. You pick the direction, and we attach a hard bid to it. Not a “starting at” number. The actual number with material allowances, fixture grades, and engineering fees baked in. You’ll review floor plans, elevations, window and door schedules, and a finish-level spec sheet that calls out cabinet grade, countertop material, backsplash, tile and flooring, and HVAC system.
Stage 3: Engineering and permit set (3-5 weeks). Our structural engineer stamps the wind-load calculations, truss design, and tie-down schedule. Lee County requires impact-rated windows or shutter protection on every opening for new residential structures, so we spec those now. We submit the permit package to the county and manage the plan review cycle. If the reviewer kicks back a comment, we answer it. You don’t chase anything. This stage ends when the permit is issued and taped to your front window.
Stage 4: Site prep, foundation, and rough-in (4-8 weeks). This is where dirt moves. We clear and grade the site, pour the slab or footers, and rough in plumbing, electrical, and mechanical. If you’re doing a detached ADU, we trench a new water and sewer lateral from the street or tie into your existing main. For garage conversions, this stage is shorter because the slab is already there, but we still cut and trench for bathroom plumbing. Once the shell is up, dried-in, and rough inspections are passed, you walk the space with our lead carpenter to confirm outlet locations, can-light placement, and any final layout adjustments before drywall goes on.
Stage 5: Interior finish and final inspections (4-6 weeks). Drywall, paint, flooring, trim, cabinet install, countertop template and fabrication, fixture trim-out, and appliance hookup. We schedule and walk through every county inspection: framing, rough mechanical, insulation, and final. When the final is signed off, your ADU is legal, rentable, and built to the code that stood up to Ian. The whole thing is covered by our 730-Day Done Right Promise. If something isn’t right, we make it right.
The decisions you’ll make on materials and specs
Every ADU we design in Three Oaks comes with a defined set of choices. None of them are “whatever the builder picks.” Here’s what you’ll weigh:
- Foundation type: slab-on-grade vs. raised pier. Slab is standard for detached units here and costs less, but if your lot has drainage issues or you’re building in a flood zone, raised piers add $8,000-$14,000 and keep your finished floor above the base flood elevation. Lee County’s FEMA maps changed after Ian, so we check current flood zone data at the feasibility stage.
- Wall assembly: concrete block vs. wood frame. Block costs more up front but handles hurricane wind loads with less engineering and insulates better in a Southwest Florida summer. Wood frame is lighter and faster but requires more strapping and shear-wall detailing to pass plan review. Most Three Oaks ADUs we build are block, matching the existing homes in the area.
- Windows and doors: impact-rated vs. standard with shutters. Impact windows are the cleaner solution and run about 30-40% more than standard units with accordion or panel shutters. If you’re building a rental ADU, impact windows eliminate the shutter-compliance headache with tenants. If it’s for family, shutters save money but require someone to deploy them before a storm.
- HVAC: mini-split vs. ducted central. A ductless mini-split system costs less to install, runs quieter, and gives you zone control room by room. For an ADU under 800 square feet, it’s almost always the right call. Ducted systems make sense in larger units or garage conversions where you can tie into an existing trunk line.
- Kitchen and bath finishes. We spec from a curated selection of brands. Cabinet lines include KraftMaid for mid-range and custom-local for full-custom. Countertops span quartz, granite, and solid surface. We’ll help you pick material grades that match how the ADU will be used: a rental unit needs durable and cleanable, not delicate and expensive.
What ADU Design & Permitting costs in Three Oaks, FL
You’ll spend $45,000 to $130,000 all-in. A garage conversion on an existing slab with no structural changes starts at the low end. A new 800-square-foot detached unit with a full kitchen, bathroom, impact windows, and a separate electrical service lands in the $90,000-$130,000 range depending on finishes and site conditions.
Five things push the number up or down:
Square footage. Every additional 100 square feet adds roughly $18,000-$25,000 in finished space, and that includes foundation, framing, roofing, drywall, flooring, paint, electrical, and HVAC.
Site access and utility runs. If your ADU site is behind a fence, down a narrow side yard, or 80 feet from the nearest sewer tap, equipment access and trenching costs climb. A long sewer lateral run with deep trenching can add $4,000-$7,000 by itself.
Existing slab condition. For garage conversions, if the existing slab is uninsulated, cracked, or below the required elevation, we either pour an overlay or cut and replace sections. That’s $3,000-$8,000 that isn’t obvious until we open it up.
Engineering requirements. Detached units need full structural calcs for wind uplift. If the soil report flags loose fill or a high water table, the foundation design gets more expensive. And if your existing home lacks hurricane straps, as many older Three Oaks homes do, tying the new structure into the existing framing requires engineered anchor retrofits that add scope.
Finish level. A rental-grade ADU with laminate counters, builder-grade cabinets, and standard fixtures costs noticeably less than a guest house with quartz counters, soft-close drawers, and tile shower walls. Our written estimate always itemizes allowances for each finish category so you can adjust the number without guessing.
Every estimate we write includes design, engineering, permit fees, materials, labor, and a line for county inspections. It does not include impact fees (Lee County charges them on new residential square footage and they vary by service area), landscaping, or furniture. We walk you through those numbers before you sign anything. Call (844) 638-7249 to schedule a free estimate at your property.
What Three Oaks homes specifically do to this job
Three Oaks homes were built mostly in the 1990s and early 2000s, which means the existing structures are concrete block on slab with stick-framed truss roofs. The construction is solid, but almost none of the pre-2002 homes have hurricane straps connecting the truss to the top plate. When you add an ADU to one of these properties, the county will often require you to bring the connection detail on the existing structure up to current code as a condition of permit approval. That’s an add-on scope you won’t see quoted by a contractor who hasn’t permitted in Lee County post-Ian.
The permitting timeline here also runs differently than it does 20 miles inland. Lee County’s building department prioritized residential rebuild permits after the storm, and while the backlog has eased, ADU plans still get scrutinized for wind-borne debris zone compliance and flood-plain elevation. We set realistic expectations from the first site visit. If your property is in a Special Flood Hazard Area, the design has to account for that from day one, or the permit gets rejected. No exceptions.
For homeowners who are already renovating the main house, we often see an ADU planned alongside a Full Kitchen Remodeling in Three Oaks or a refresh of Cabinets & Countertops in Three Oaks. Bundling the projects under one permit set can save on design fees and let our crews sequence the work without overlapping disruptions. It also puts the entire property under our 730-Day Done Right Promise, which matters when you’re investing in more than one structure.
This is Home Additions & ADU in Three Oaks work at its most specific. The codes, the soil, the wind maps, and the inspection culture are all local. The company you hire should know them cold.
Serving Three Oaks, FL - Our Local Coverage Area
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Frequently asked - ADU Design & Permitting in Three Oaks
Yes. Every ADU in unincorporated Lee County requires a building permit, and depending on your lot, you may also need a zoning clearance, a tree-removal permit, and an impact-fee assessment. We handle the full permit package, from engineered drawings to final sign-off, so you never have to walk a set of plans into the county building yourself.
Design and permit approval typically takes 8 to 12 weeks. Site work and construction add another 3 to 6 months. The biggest variable is the county plan-review queue, which fluctuates seasonally. We submit complete, engineer-stamped packages that reduce the back-and-forth, and that keeps the timeline as short as the process allows.
A straight garage conversion where the slab, walls, and roof stay as-is is the most cost-effective ADU path for Asphalt Driveways & Resurfacing in Three Oaks customers considering an ADU. You still need to add a bathroom and kitchenette, which means cutting the slab for drain lines and running new water and electrical. The structural shell stays intact, but plumbing rough-in is not optional if you want a legal, habitable unit. Expect to spend $30,000-$60,000 depending on finish level and utility run distances.
A new detached ADU runs $90,000 to $130,000 for a complete unit with foundation, framing, roofing, drywall, mechanical, and finishes. A garage conversion on an existing slab starts around $45,000. The gap is the cost of new foundation, exterior walls, and a roof structure. Both include design, engineering, permits, and finishes. Call (844) 638-7249 and we’ll price both options against your actual property so you can compare real numbers, not website ranges.
Every ADU we design and build in Three Oaks is covered by our 730-Day Done Right Promise. It’s one of the longest workmanship guarantees you’ll find on residential construction in Southwest Florida. If something isn’t done right, we make it right, full stop. That covers structural, finish, and systems workmanship for two full years from final inspection.
Get a free ADU design & permitting estimate in Three Oaks, FL
If you’re considering an ADU on your Three Oaks property, let’s walk the site together. We’ll measure, check setbacks, discuss layout options, and give you a written, line-item estimate that shows exactly where the money goes. No pressure, no vague ranges, and no cost to you for the visit. Call (844) 638-7249 to schedule yours. A live person answers, day or night, and we’ll have a background-checked estimator at your home within days.
Written by Derek Hollenbeck, Owner at Groundwork Construction Co., serving Three Oaks and all of Lee County.