ADU Site Plans: What Cities Actually Check
Quick answer
Every ADU application needs a site plan, and it gets a closer read than any other residential drawing: setbacks (often capped by state law at levels friendlier than the normal table), separation from the main house, access, parking, and utility routing. Conversions mostly document existing conditions; detached new units get the full treatment. ADU rules change yearly, so verify your city's current ordinance before drawing anything.
Accessory dwelling units are the fastest-moving corner of residential permitting. States keep loosening the rules to encourage them, cities keep adjusting their review standards to keep up, and homeowners are caught in between with a simple question: what drawing does the application actually need? Here is the site-plan side of the answer, in plain English.
Why ADU site plans get extra scrutiny
An ADU is a dwelling, someone will live in it, and that changes what the reviewer checks on the site plan compared with a shed or garage:
- Setbacks, with ADU-specific rules. Many states now cap how much setback a city can demand for small ADUs (4-foot side and rear setbacks are a common modern standard), which often makes the ADU rules more generous than the ordinary accessory-structure table. The site plan is how you claim those numbers.
- Separation and access. Distance from the main house, plus a path from the street or a shared entrance, because emergency access matters for dwellings.
- Parking. Some jurisdictions require a replacement or additional space and want it drawn; many have dropped ADU parking minimums entirely. The plan should show the parking situation either way.
- Utilities. Reviewers increasingly want utility routing noted: where water, sewer, and power reach the unit. On conversions this can be a note; on detached new builds it is often its own sheet.
- Lot coverage and open space. A dwelling-sized footprint moves the coverage math more than a shed does, and some ADU ordinances add open-space minimums.
The pattern: same drawing type you would submit for any project, held to a closer read. Every element from our Pre-Submission Checklist still applies; the ADU rules add items on top.
The three ADU paths, and what each needs
- Garage or basement conversion. The footprint does not change, so the site plan mostly documents existing conditions: the structure, setbacks as they stand, parking before and after. Usually the simplest drawing of the three.
- Attached addition. The site plan shows the new footprint against setbacks and coverage, exactly like any addition, and travels with stamped construction drawings.
- Detached new ADU. The full treatment: footprint, setbacks, separation, access path, utility routing, parking. This is the one where cities look hardest at the site plan.
Honest scope: where we fit, and where we do not
Our drafting service covers site plans for decks, fences, sheds, patios, and garages, and we do not currently offer a full ADU submittal package. For a complete ADU application, your designer or architect produces the site plan as part of the stamped set, and that is the right way to do it, because ADU site plans need to stay consistent with the construction drawings they accompany.
Where our work still helps you:
- Feasibility first. Before paying a designer, many homeowners want to know whether an ADU can even sit on the lot. Your county GIS records and the method in our drawing walkthrough let you rough out setbacks and coverage in an afternoon, for free.
- The related projects. If your ADU plan starts with building a garage now and converting later, or fencing the yard for a separate entrance, those site plans are exactly what we draft every day.
- Checking the set. When your designer's site plan arrives, the checklist and complete guide tell you what the city's reviewer will look for on it.
Before you start: the two-minute checks
ADU rules are the most jurisdiction-specific in residential permitting and they are changing yearly, in the homeowner's favor in most states. Before sketching anything: search "[your city] ADU ordinance" for the current setback, size, and parking rules; ask whether your city offers pre-approved ADU plans (a growing number do, and they can cut months off review); and confirm whether owner-occupancy or deed requirements apply. Then verify everything with the building department, because this is the one corner of permitting where a 2024 blog post is already out of date.
For the broader permit process, start with the garage permit guide for conversions or the complete guide to site plans for the drawing fundamentals.
Frequently asked questions
Do I need a site plan for an ADU permit?
Yes, universally. Every ADU application includes a site plan showing the unit's footprint, setbacks, separation from the main house, access, and usually parking and utility routing. For conversions the plan mostly documents existing conditions; for detached new units it gets the closest review of any residential site plan.
Are ADU setbacks different from normal accessory structure setbacks?
Often, and frequently more generous. Many states have capped the setbacks cities can require for qualifying ADUs, with 4-foot side and rear setbacks a common modern standard, which can be less than the ordinary accessory-structure table demands. Your city's current ADU ordinance is the authority, and it is worth reading this year's version, because these rules keep changing.
Can I use a pre-approved ADU plan from my city?
A growing number of cities publish pre-approved ADU building plans that dramatically shorten review. You still need a site plan for your specific lot showing where the pre-approved unit sits, its setbacks, access, and utilities. Check your city's ADU program page; the time savings are real.
Does a garage conversion ADU need a new site plan?
Yes, though it is usually the simplest kind: the footprint already exists, so the plan documents current conditions, setbacks as built, and the parking situation before and after conversion. The heavier drawings for a conversion are the floor plan and the construction set, which come from your designer.
Permit requirements vary by city, county, and state. The information in this guide provides general guidance based on common building codes and practices across the US. Always verify requirements with your local building department before starting your project.