Three kinds of ADU, three drawings
Name the type on the sheet. Reviewers apply different setbacks to each:
- Detached, new construction. A separate backyard building. The site plan shows a new footprint, the gap between it and the house, and the yards around it.
- Attached. An addition that is a separate unit, with its own entry. It is drawn like a home addition, but the ADU ordinance controls size, parking, and setbacks.
- Conversion. A garage, basement, or other existing space turned into a unit. The footprint often does not grow. The site plan still shows that space, the new entrance, and utility changes. A garage conversion should say the parking stall is going away.
A junior ADU, where your state has that category, is a smaller unit inside the main house. Show the portion of the house it occupies and the separate entrance if one is required. Do not draw it as a new backyard building.
What the site plan needs
| Element | Why |
|---|---|
| Property lines, lot area, zoning district, easements | Every standard is measured from these |
| Existing primary dwelling | An ADU is accessory to it; show the house even for a conversion |
| ADU footprint, floor area, and height | Size caps are usually on interior area, not only the pad |
| Setback dimensions to each lot line and to the house | The zoning check |
| Entrance and path to the street | The unit needs a way in that is not through someone else's bedroom |
| Parking, if any is required | Show the stall, or note that none is required and why |
| Water, sewer or septic, and electrical path | A backyard unit still has to connect; septic lots need the tank and field |
| North arrow, scale, address | Identifies the sheet |
The site plan is the site-specific half of the permit. Floor plans, elevations, structure, and energy compliance are the other half. In states that offer pre-approved ADU plans, you still submit a site plan for the lot — the pre-approved set does not know where your property lines are.
Setbacks and parking are not one national rule
Start with your city's ADU handout. If your state has an ADU statute, the handout has to follow it, and a local zoning counter that quotes only the old single-family setbacks may be wrong.
California is the clearest published example. The state's Department of Housing and Community Development March 2026 ADU handbook, summarizing Government Code ADU law, describes standards cities cannot use to block a unit:
- For a new-construction ADU, a city cannot require more than 4 feet of side or rear setback.
- A conversion of existing space generally keeps the setbacks it already has, as long as fire and safety are met. Rebuilding on the same footprint is treated the same way.
- Lot coverage, floor-area ratio, open space, front setback, and minimum lot size cannot be applied so strictly that they prevent at least an 800 square foot ADU with those 4-foot side and rear setbacks.
- When a city may require parking at all, the cap is generally one space per ADU or per bedroom, whichever is less, and tandem parking on a driveway counts. Several common cases, including ADUs near transit and conversions, cannot be required to add parking.
- Height limits depend on the case. The handbook describes 16, 18, or 20 feet in different situations. Use the figure that matches your project, not a single default.
Those are California rules. They are not a permit in any other state. Several other states also limit what a city can demand for an ADU; the numbers differ. Use your state housing agency's ADU page, then the city handout, and type those distances into the drawing.
How to draw it free in ZoneMapper (about an hour)
1. Open the ADU template or your own map
Start from template and choose ADU if you want a sample backyard unit, a house, a dimension, and placeholder compliance numbers. The banner on that sample stays until you clear it. For a real application, upload a survey or start from your address. GIS parcel lines are a starting outline, not a survey.
2. Trace the lot and the primary house
Use Lot boundary if the outline is not already loaded, then Finish lot boundary. Draw the main house and mark it Existing.
3. Draw the unit
For new construction, draw the ADU with Rectangle at the real footprint and leave it Proposed. Label the floor area and height with Text — a 20 by 24 pad is not the same fact as the interior square footage the ordinance caps. For a conversion, draw the existing garage or basement footprint, mark it existing, and note “convert to ADU” rather than inventing a new building.
4. Dimension setbacks, parking, and access
Dimension the unit to each lot line and to the house. Enter the ADU setbacks in the Setbacks panel, not the shed setbacks from a different handout. If a parking space is required, draw it and label the size; if it is not, put that note on the plan so the reviewer does not assume you forgot it. The compliance fields can record proposed height and parking counts next to the limits you were given.
5. Export
Export the PDF with a title block, north arrow, and scale. Submit it with the architectural set, and with the utility plan your building department asks for on a new detached unit.
Common reasons ADU site plans are rejected
- Shed or house setbacks used instead of the ADU setbacks
- Floor area missing, so the size cap cannot be checked
- A garage conversion that does not say the parking stall is removed, or that shows replacement parking the statute does not allow the city to require
- No path from the unit door to the street
- Septic or easement left off the drawing on a lot that has them
FAQ
Can I put the ADU in the front setback?
Only if your state or city allows it. In California, a front setback can still be applied, except that it cannot be used to block at least an 800 square foot unit with 4-foot side and rear setbacks. Elsewhere, assume the front setback applies until the handout says otherwise.
Is a site plan enough?
No. Living space needs a floor plan, elevations, and usually energy and structural sheets. The site plan is how zoning confirms the unit fits on the lot. If you are using a pre-approved building design, this site plan is the piece that is still unique to your property.
Do I need a survey?
For a new detached building, plan on one if the unit is near a setback or an easement. Conversions of existing space are sometimes accepted on the survey you already have. GIS lines are fine for a first layout and weak for a foundation.
More permit guides
ZoneMapper is a drafting aid. ADU size, height, setbacks, parking, and owner-occupancy rules depend on state law and the local ordinance. The California figures on this page follow the state's March 2026 ADU handbook and are not a permit. Confirm the current handout for your address before you submit or build.