ADU permit plans: the drawings you need for a backyard cottage

Published October 3, 2026 · TraceBIM permit guides

An accessory dwelling unit, or ADU, is a second, smaller home on the same lot as a house. It may be a detached backyard cottage, an apartment over a garage, or a unit attached to the main house. Because an ADU is a complete home with its own kitchen and bathroom, its permit set is usually more complete than for other residential projects. Here is what to expect.

This guide is general information, not legal, code or engineering advice. Permit rules differ between states, counties and cities and change over time. Always confirm requirements with your local building department.

Do you need a permit?

Yes. An ADU is a new dwelling, so it needs a building permit almost everywhere, and often planning or zoning review as well. Many areas have made ADUs easier to build in recent years, but the rules on size, height, placement and parking differ widely between states, counties and cities.

Before you draw anything, find your city or county's ADU page or call the planning desk. Ask about allowed size, height, distance from property lines, parking, owner-occupancy rules, and utility connection requirements. Confirm everything with your local building department; do not rely on what applies in a neighboring town.

The drawings you'll typically need

A typical ADU submission includes many of these sheets:

• Cover sheet: project address, owner, scope of work, a sheet index, and basic project data such as lot size and floor areas.
• Site plan: the lot with property lines, existing house, new ADU, distances between buildings and to property lines (setbacks), driveways, trees, and utility routes.
• Floor plan: every room with dimensions, doors, windows, kitchen and bathroom layout.
• Elevations: all four sides of the ADU, with heights, materials, and window positions.
• Building sections: cut-through views showing foundation, floor, walls, roof, ceiling heights and insulation.
• Roof plan: roof shape, slopes and drainage.
• Foundation and framing plans: often prepared or reviewed by an engineer for new structures.
• Structural details and calculations, where required.
• Electrical, plumbing and mechanical plans: outlets, lighting, fixtures, water heater, heating and cooling.
• Energy compliance documents: forms or calculations showing the unit meets local energy rules.
• Utility information: how water, sewer, power and gas reach the ADU.

An ADU converted from an existing garage or basement may need fewer structural sheets, but usually still needs most of the rest.

What plan checkers commonly look for

• Setbacks. The required distances from property lines and from other buildings. Show them clearly on the site plan.
• Size and height limits. Floor area and building height, calculated the way your jurisdiction defines them.
• Fire separation. Walls close to property lines or other buildings may need fire-resistant construction and limited openings.
• Egress. Sleeping rooms usually need an emergency escape window or door.
• Ceiling heights, light and ventilation in habitable rooms.
• Smoke and CO alarms, and in some areas fire sprinklers.
• Structure. Foundation, framing, and how loads travel to the ground. This is where engineering is often required.
• Utilities. Separate or shared connections, sewer capacity, and electrical service size.
• Energy compliance for insulation, windows, heating and water heating.
• Address and access. How emergency responders will find and reach the unit.

Common reasons submissions get sent back

• A site plan without setback dimensions, or one that does not match the survey.
• Floor area or height calculated differently from the local definition.
• Drawings that disagree with each other, such as a window shown on the plan but missing from the elevation.
• Missing sections, so wall, roof and insulation build-up is unclear.
• No structural information for the foundation or roof framing.
• Missing energy compliance paperwork.
• No stamp where the jurisdiction requires one.

How to make the drawings yourself with TraceBIM

TraceBIM is a web app (it works on an iPad too) that turns a rough sketch or a plain description into professional drawings. You do not need to know drafting software or drafting vocabulary.

1. Sketch or describe your space

   Describe the unit the way you would to a builder: "Detached 1-bedroom cottage, about 24 by 28 feet, kitchen along the back wall, bathroom next to the bedroom, gable roof." Or draw a rough sketch in the app. Start from your measured lot dimensions and setbacks.

2. Let the AI draft the drawings

   TraceBIM's AI drafts floor plans, elevations and sections from what you gave it, with dimensions, standard drawing symbols and a title block on each sheet.

3. Review and adjust

   Check the layout and dimensions, make sure every window on the plan appears on the elevations, and add your notes. Ask the AI for changes in plain language, or edit directly. If an engineer or architect is involved, share the set with them so their work starts from clear drawings.

4. Export a PDF set

   Export the sheets as a PDF and submit them with your application, or hand them to your contractor, designer or engineer.

Be realistic about what the app does and does not cover. TraceBIM makes the drawings. Some things on the checklist above come from elsewhere: a property survey, energy compliance forms, product data sheets and, when required, engineering calculations or a professional's stamp. TraceBIM's Studio plan is free during early access, no credit card is needed, and every new workspace comes with starter AI credit.