Why the Lot Decides Before the Design Does
An ADU is a second home on a lot that was approved for one. That is why the first question is never what the unit should look like. It is whether your parcel can carry a second unit at all, and under what limits. Zoning sets the ceiling: maximum unit size, setbacks from each property line, how much of the lot can be covered by roof and pavement, height, parking, utility connections, and in some places a rule about who has to live on the property.
Design that starts before that answer is design you may have to throw away. Every accessory dwelling unit project we take on opens with a written read of what the parcel allows, because finding out late is not a revision. It is a redesign.
What Florida Law Says, and What Your City Decides
Florida statute defines an accessory dwelling unit as an ancillary or secondary living unit with its own kitchen, bathroom, and sleeping area, either inside the primary house or elsewhere on the same lot. The same statute says a local government may adopt an ordinance to allow accessory dwelling units in any area zoned for single-family residential use. Read those two sentences together and the shape of the problem is clear: the state names the thing, and your local ordinance decides whether you can build it.
So the same question gets different answers in the City of Orlando, in unincorporated Orange County, and in the county next door. Orlando publishes a step-by-step guide that lists the zoning districts where an ADU is possible, points you to the city property lookup to confirm your own, and caps the unit at 700 square feet inside a historic district, where a certificate of appropriateness comes before the building permit. Unincorporated Orange County publishes its own permit page, which requires the house and the ADU to stay under one ownership, requires the owner to occupy one of the two units, and limits ADUs to homestead properties.
What a Local Ordinance Usually Controls
- Maximum size of the unit, often tied to the size of the primary home
- Setbacks from the side and rear property lines, and separation from the main house
- Lot coverage and impervious surface limits, which count the driveway and walkways
- Height, roof form, and whether the unit has to read as part of the main house
- Parking, including whether a converted garage has to be replaced with parking elsewhere
- Utility connections: whether the unit shares the existing service or needs its own
- Who lives there, including owner occupancy conditions and short-term rental rules
Every local rule named in this article comes from that jurisdiction's own published page, linked in the sources below, and was accurate when this was written. Ordinances change, and the only rules that govern your project are the ones your address falls under. Confirm current requirements with your local building department before you commit to anything, or send us the address and we will confirm them with you.
Three Ways to Add an ADU, and What Each One Demands in Drawings
Detached unit, attached addition, garage conversion. Owners usually arrive with one of the three already in mind, chosen from a photo. The lot, the existing house, and the local ordinance are what actually decide which of them is available, and each path sends the drawing set in a different direction.
| Path | What you are building | What the drawings have to prove | The usual sticking point |
|---|---|---|---|
| Detached unit | A small separate home in the rear yard | Setbacks on every side, lot coverage, height, a utility run to the new building, grading that moves water away from both roofs | Space. The yard has to absorb the unit, the separation from the house, and the parking. |
| Attached addition | New enclosed living area sharing a wall with the house | How the new roof and walls meet the existing ones, fire separation between the two units, a separate entrance that works on site | The connection. Existing framing and floor levels have to be measured, never assumed. |
| Garage conversion | Living space inside a footprint that is already standing | That the existing slab, walls, and openings can legally become habitable: ceiling height, escape openings, insulation, separation | Parking and slab. The car has to go somewhere, and the slab was poured to park a car on. |
Garage Conversion Plans Start With Measuring, Not Drawing
A garage conversion looks like the shortest path and is often the slowest one to document. Nothing about the existing building can be assumed: the slab elevation against the house floor, the header over the old garage door, the wall framing, the panel capacity, the way water runs off the driveway today. All of it is measured and drawn as it stands before the new unit is drawn over it. That is the same starting point as any home addition, and it is why a conversion set carries two floor plans, existing and proposed, instead of one.
What a Permit-Ready ADU Set Contains
The list below tracks what Orange County publishes for a residential ADU permit. Other jurisdictions ask for variations of the same package, because they are all reviewing the same two things: your drawings against the Florida Building Code, and your drawings against the local amendments layered on top of it.
- A site plan or survey locating the proposed unit on the lot
- A lot grading and drainage plan with the finished floor elevation
- Existing and proposed floor plans with every room use labeled
- Elevations, sections, and the details a builder can price and build from
- An emergency escape and rescue opening called out in every sleeping room
- Fire separation between the units, detailed to the code section the jurisdiction cites
- Mechanical calculations and the energy form the county asks for
- Truss layouts and the supporting engineering when the unit is framed that way
- The product approval sheet for windows, doors, and roofing
- A set signed, dated, and sealed by the licensed professional that jurisdiction accepts
That package is what a permit-ready plan set is. Not a prettier drawing, a complete one, assembled so plan review has nothing left to ask for. Every item missing from it is a correction letter with your name on it and another trip through the queue.
Why Downloaded ADU Plans Stall at the Permit Counter
A plan bought online is a drawing of a building with no lot attached to it. It has no site plan for your parcel, no survey, no grading and drainage, no product approval for your wind zone, no read of your setbacks, and no seal from anyone licensed where you are building. Plan review is not judging the taste of the layout. It is checking a specific building against a specific parcel under a specific code edition, and a catalog sheet answers none of the three.
A pre-reviewed plan is a different animal, and it is worth knowing about. The City of Orlando has announced a library of ADU plans reviewed by city staff in advance and sold at a fixed price by the firm that drew them, listed on the city page as expected in fall or winter of 2026. Even those do not arrive finished: the lot-specific work, the site plan, the grading, the utility connections, and the historic review when one applies still have to be produced for your address. Check the city page for the current status of the program before you build a schedule around it.
The Order the Work Happens In
- Confirm the lot. Zoning district, minimum lot size, setbacks, coverage, parking, and any occupancy condition, checked against your parcel before anything is drawn.
- Document what exists. Measure the house, the garage, the slab, the services, and the site. On a conversion this is the longest step, and skipping it is what produces a correction letter three months later.
- Agree on the layout. One floor plan, reviewed and approved by you, before elevations and details are developed on top of it.
- Produce the construction documents. Drawings, engineering coordination, mechanical calculations, product approval, assembled as one coordinated set.
- Submit and work the comment cycle. The jurisdiction reviews, comments come back, the set is corrected and resubmitted until the permit is issued.
- Build and inspect. Inspections during construction, then the final approval that lets anyone live in the unit.
Step two is the one owners are least prepared for. If the house has no current drawings, as-built drawings are the first deliverable of the project and everything else in the set is drawn on top of them.
What Actually Slows an ADU Down
- No survey, or a survey too old to show what is on the lot today
- Service capacity: an existing connection that cannot carry a second kitchen and bathroom
- Impervious surface already near the limit, so one more walkway pushes the lot over
- Historic district review, which is a separate approval running on its own calendar
- Recorded deed restrictions or an association that limits what zoning would otherwise allow
- Occupancy or homestead conditions discovered after the design is finished
- A comment cycle left sitting, which is the only delay on this list a design team can close in days
Where to Start if You Are Thinking About One
Start with the address and with what you want the unit to do: a rental, a suite for a parent, an office with a bathroom, a place for an adult child who is back home. Those answers move the size, the entrance, the parking, and sometimes the question of whether the unit is allowed at all. Line Arch Design works in Orlando and Central Florida in person and remotely across the rest of Florida for documentation and permitting, and we confirm what a lot allows before a drawing is quoted. More of what owners ask before they start is answered on the FAQ page.
