What a Junior ADU & Interior Conversion Actually Costs and Takes in Lely
A junior ADU and interior conversion in Lely typically runs $45,000 to $130,000 and takes 10 to 16 weeks from the first wall opened to the final walkthrough. The job converts an existing attached space, a large bedroom suite, a bonus room over the garage, or a ground-floor den with its own exterior door, into a fully self-contained dwelling unit with a kitchenette, sleeping area, bathroom, and separate entrance. Call us at (844) 638-7249 for a free, written estimate that breaks down exactly what the number includes. No vague ranges, just a real price for your specific Lely home.
How a Junior ADU Conversion Comes Together, Stage by Stage
We walk every Lely homeowner through five clear stages before the first piece of trim goes up. Each stage has a decision point, and we tell you what to expect before you need to ask. Here is how the process actually unfolds.
Stage 1: Design Lock and ARC Submission (Weeks 1-3)
We measure the existing space, verify load paths, and produce a floor plan that works within your home’s current footprint. For Lely Resort properties, this is also when we prepare the Architectural Review Committee submission package, material boards, roofline elevations if any exterior work touches the existing structure, and site plans showing the new entrance and any grading changes. ARC review in Lely Resort adds two to four weeks to the front end, and we build that into the schedule from day one. You pick your finishes at this stage so we can lock pricing before permits are pulled.
Stage 2: Permitting and Pre-Construction (Weeks 3-5)
Collier County requires a full building permit for any interior conversion that adds a kitchen and bathroom. We submit engineered drawings showing the new plumbing, electrical subpanel, mechanical tie-ins, and egress compliance. The county looks closely at wet-wall placement relative to existing drain lines and the water meter’s capacity to handle an additional dwelling’s demand. While the permit processes, we order long-lead items, windows, doors, cabinetry, and any custom millwork, so nothing sits idle once the crew starts.
Stage 3: Rough-In and Infrastructure (Weeks 5-8)
Demolition of non-load-bearing walls happens first, usually two to three days. Then we trench for the new bathroom and kitchenette drain lines, which in Lely means working with slab-on-grade construction. Cutting into a concrete slab on a CBS home takes precision and often reveals surprises: old cast-iron waste lines that have corroded in Florida’s acidic soil, or a high water table that seeps into the trench during the rainy months. We install the dedicated electrical subpanel, run new circuits per code, and rough in the mini-split HVAC if the existing system cannot be balanced to serve the new unit independently. The rough plumbing and electrical inspection happens before any drywall goes up.
Stage 4: Dry-In, Insulation, and Interior Finish (Weeks 8-13)
New exterior-grade door installation with proper flashing and wind-rated hardware comes next, and that door must meet current Florida Building Code impact requirements even if it serves what was previously an interior room. We insulate all new walls to code minimum or better, hang and finish drywall, and start the interior trim package. The kitchenette gets its cabinets, countertops, and appliances. The bathroom gets tiled, the vanity set, and fixtures trimmed out. Paint, flooring, and lighting go in last. Throughout this stage, humidity control is critical in Lely: if the air conditioning is not cycling during the day, drywall mud and paint cure times stretch, so we run temporary dehumidification when needed.
Stage 5: Final Inspections and Handover (Weeks 13-16)
Collier County inspects plumbing, electrical, mechanical, and the final building envelope. If the property is in Lely Resort, the ARC may also do a compliance walk to confirm the finished conversion matches the approved submission. We walk the unit with you, test every outlet and fixture, and hand you a closeout packet with all permits, warranties, and a maintenance schedule. You are ready to rent or house family the day the final inspection sticker goes on the panel.
The Options You Will Choose Between
A junior ADU conversion gives you real choices that change how the space lives and what it costs. Here are the decisions that move the needle most.
- Kitchenette vs. full kitchen. A kitchenette with a two-burner cooktop, undercounter refrigerator, microwave, and bar sink keeps the plumbing simple and costs less. A full kitchen with a range, vent hood, dishwasher, and 30-inch refrigerator requires a gas or 240V electrical run and a dedicated exhaust path, which adds $8,000 to $15,000 to the project in a slab-on-grade Lely home where running new lines means trenching concrete.
- Wet bath vs. divided bathroom. A wet bath, a fully waterproofed room where the shower and toilet share open floor space, saves square footage and cuts tile and glass costs significantly. A divided bathroom with a separate shower enclosure and vanity alcove feels more residential and rents higher but adds plumbing fixture counts and framing complexity.
- Mini-split vs. tied to existing HVAC. A ductless mini-split heat pump gives the ADU tenant independent temperature control and costs $3,500 to $6,000 installed. Extending your home’s existing ducted system is cheaper upfront but creates disputes over the thermostat and can overload an older air handler not sized for the extra square footage.
- Interior door vs. impact-rated exterior door. By code, any new exterior door in Lely must be impact-rated or protected by an approved shutter system. We default to an impact-rated fiberglass or steel door with a multipoint lock, which runs $2,500 to $4,500 installed depending on sidelight configurations. An interior-grade door cannot legally serve as the unit’s primary entrance.
- Flooring: luxury vinyl plank vs. tile. LVP installs faster, costs less per square foot, and handles humidity without cupping. Porcelain tile feels cooler underfoot, which matters in Lely’s climate, and lasts decades longer, but the material and labor cost runs roughly double. For a rental unit, LVP in a wood-look finish is the most common choice we see.
What a Junior ADU & Interior Conversion Costs in Lely, FL
A realistic budget for this work in Lely lands between $45,000 and $130,000. The spread is wide because five variables push a project toward one end or the other, and Lely’s specific housing stock amplifies some of them.
Square footage of the converted space. A 350-square-foot bonus room conversion lands at the lower end. A 700-square-foot ground-floor suite with a separate living area, sleeping alcove, and full bath pushes toward the upper end. Every additional square foot adds framing, drywall, flooring, lighting, and HVAC load, which compound linearly.
Slab plumbing work. Most Lely homes sit on a concrete slab. Adding a bathroom and kitchenette where no drain lines exist means cutting and trenching the slab, tying into the existing waste stack, and backfilling with compacted fill. If the cast-iron waste lines are original and corroded, as we regularly find in 1990s-era Lely Resort villages, replacement of a section of main line adds $3,000 to $7,000 to the job before any finish work begins.
Electrical service capacity. A junior ADU with its own kitchen appliances, bathroom exhaust, and mini-split may push an older 150-amp panel past its load calculation. Upgrading to a 200-amp service and running a subpanel to the new unit adds $3,500 to $6,000. We check this during the estimate so the number does not change later.
Finish level. Builder-grade cabinets, laminate counters, and fiberglass shower surrounds keep the budget trim. Semi-custom cabinetry, quartz counters, a tiled shower with a glass enclosure, and upgraded plumbing fixtures can add $15,000 to $25,000 to the total. We quote both levels transparently so you choose what fits your rental strategy or family needs.
ARC compliance in Lely Resort. If the conversion touches the exterior, adding or relocating a door, changing window sizes, or altering any elevation visible from the street or golf course, the Lely Resort ARC must approve the materials and design. ARC-required upgrades to door style, roof tie-in trim, or exterior paint matching can add $1,500 to $4,000 that a non-resort project would not carry.
Every estimate we write is a fixed-price line-item quote. What is included: all demolition, rough and finish carpentry, plumbing, electrical, HVAC, drywall, paint, flooring, fixtures, and the permit package. What is not included unless specified: furniture, window treatments, appliances beyond the kitchenette package, and any upgrade you add after the contract is signed. Call (844) 638-7249 to schedule a free on-site estimate and get a real number for your specific floor plan.
What Lely Homes Specifically Do to This Job
Lely is not generic southwest Florida suburbia. It is dominated by the Lely Resort master-planned golf community, and that fact alone reshapes how a junior ADU and interior conversion gets permitted and priced. Every project that touches an exterior wall, adds a door, or alters a roofline visible from the street or course must pass through the Lely Resort Architectural Review Committee before Collier County will process a building permit. The ARC enforces strict material palettes, roofline standards, and setback overlays that off-the-shelf plans routinely violate. We have built enough in Lely Resort to know that an ARC submission needs a full material board, elevation drawings, and a site plan showing the new entrance in relation to lot lines and swale buffers on the first pass. Contractors who treat the ARC as an afterthought get rejected, and a rejection resets the clock by three to five weeks.
The housing stock itself drives how we approach the work. The vast majority of Lely homes are 1990s-to-early-2000s concrete block stucco construction with original barrel tile roofs and single-pane windows. That means the interior space you want to convert was never framed with a future dwelling unit in mind. We regularly open walls and find undersized headers over existing openings, no continuous load path from the top plate to the footing, and electrical panels already near capacity. The conversion almost always requires structural upgrades that a newer home or a stick-framed house would not. And because Lely sits at extremely low elevation near the Everglades fringe with a water table as shallow as 18 to 24 inches below grade, any trenching inside the slab for new drain lines often hits groundwater during the May-through-October rainy season. We plan dewatering into the schedule and the price from the start.
Snowbird scheduling adds another layer. Many Lely homeowners want the heavy construction done between May and October while they are up north, which is exactly when afternoon thunderstorms shut down exterior work daily and hurricane-season supply chains slow window and door deliveries. We build a realistic wet-weather buffer into the timeline and communicate it upfront. For homeowners who want to pair the junior ADU with other interior work, we often coordinate with Kitchen Design & Layout in Lely or Small & Partial Kitchen Remodels in Lely so both scopes share one permit cycle and one crew mobilization, saving time and reducing the total disruption to the home.
A junior ADU conversion is ultimately part of the wider Home Additions & ADU in Lely landscape, but it is distinct from a detached new build. The existing structure gives you a head start on cost and timeline, but it also imposes constraints that a ground-up ADU avoids. Our Home Additions & ADU team has worked on enough Lely Resort properties to know those constraints before the first saw cut. If you are in Lely and considering turning an underused room into income-producing space or a private family suite, we can walk the property and tell you honestly what is possible and what it will cost.
Serving Lely, FL - Our Local Coverage Area
We’re based in the Lely 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 Questions About Junior ADU & Interior Conversion in Lely
Plan on 10 to 16 weeks from demolition to final inspection. The biggest variable in Lely is the Lely Resort ARC review, which adds two to four weeks to the front end if your property is within the resort boundaries. The rainy-season months of May through October can also push exterior work, like door installation and any stucco patching, by a few days at a time due to afternoon shutdowns. We build these buffers into the schedule we give you at contract signing. Call (844) 638-7249 and we will map a timeline against your specific start window.
Yes. Collier County requires a full building permit with plumbing, electrical, and mechanical sub-permits for any conversion that adds a kitchen and bathroom to create a separate dwelling unit. If the work touches an exterior wall or adds a new entrance, the permit also triggers a zoning review for setback compliance and, in Lely Resort, the mandatory Architectural Review Committee approval. We pull every required permit and handle the inspections so you never have to chase the county. Unpermitted conversions create serious liability and resale problems; we will not do them.
Rarely. A junior ADU by definition includes a kitchenette and a bathroom, both of which need water supply, drain lines, and dedicated circuits. If the room you want to convert sits directly adjacent to an existing bathroom or kitchen wet wall, we can often tap into those lines and minimize slab trenching. If the space is on the opposite side of the house from existing plumbing, the job becomes more invasive and more expensive. The electrical demand of a second kitchen and a mini-split HVAC unit almost always requires a subpanel, even when the main panel has open breaker slots. We assess both during the free estimate and show you exactly where the new runs will go.
Most junior ADU and interior conversion projects in Lely fall between $45,000 and $130,000. A straightforward conversion of a 400-square-foot ground-floor bedroom into a studio with a kitchenette and three-quarter bath on the same side of the house as existing plumbing lands near the lower end. A larger conversion with a full kitchen, separate living and sleeping zones, a divided bathroom, impact door, and structural upgrades on a 1990s CBS home pushes toward the upper end. The five variables that move the number are square footage, slab plumbing scope, electrical service upgrades, finish level, and ARC compliance requirements in Lely Resort. We quote a fixed price, not an estimate that drifts upward after demolition starts. Call (844) 638-7249 to get a written quote for your specific home.
Every junior ADU and interior conversion we complete in Lely is covered by our 730-Day Done Right Promise. If something is not done right within two full years of completion, we make it right at no cost to you. This covers workmanship across every trade: framing, drywall, plumbing, electrical, flooring, millwork, and finish work. Material and appliance warranties from the manufacturer run separately and we register every product on your behalf. Our background-checked, uniformed crew stands behind the work, and you reach a live person when you call, day or night.
Get a Free, Written Estimate for Your Lely Junior ADU Conversion
We will walk your Lely home, measure the space, check the panel, map the plumbing, and tell you honestly what a junior ADU conversion costs and how long it takes. No sales pitch, no vague numbers that move later. You get a fixed-price, line-item quote you can take to your HOA or your lender. Call (844) 638-7249 to schedule your free on-site estimate. Derek Hollenbeck and our Home Additions & ADU team have built in Lely Resort long enough to know what the ARC needs on the first submission, and that alone can save you a month.
Written by Derek Hollenbeck, Owner at Groundwork Construction Co., serving Lely homeowners with fixed-price construction and the 730-Day Done Right Promise.