Accessory dwelling units — ADUs, in-law suites, granny flats, backyard cottages — are booming across the US as cities loosen restrictions to address housing shortages. But the permit process is more involved than a standard home addition. This guide covers exactly what drawings most cities require for an ADU permit.

What Is an ADU?

An accessory dwelling unit is a secondary housing unit on a single-family lot. It can be detached (a separate structure in the backyard), attached (an addition to the main home), or converted (a garage, basement, or attic turned into living space). Each type has slightly different permit requirements.

Drawings Typically Required for an ADU Permit

Most cities require a full drawing package for ADU permits. This typically includes:

• Site plan: Shows the ADU location, setbacks, existing structures, utilities, and property boundaries
• Floor plan: Shows room layout, dimensions, door/window locations, and square footage of the ADU
• Elevation drawings: Shows exterior views of the ADU from all four sides
• Foundation plan: Required for detached ADUs and additions
• Electrical, plumbing, mechanical plans: Often required in addition to architectural drawings

ADU Site Plan Requirements

The site plan for an ADU is more detailed than a standard permit site plan because it must show:

• Primary dwelling and ADU location and dimensions
• All setbacks (typically 4–5 feet from property lines)
• Parking spaces (some cities require additional parking)
• Utility connections for the ADU
• Lot coverage calculation (ADU + existing structures vs. lot size)
• Owner-occupancy requirements in some jurisdictions

ADU Setback Requirements

ADU setback requirements vary widely by state. California has mandated 4-foot minimum setbacks for most ADUs. Other states allow cities to set their own rules. Common patterns:

• Detached ADU: 4–10 feet from rear and side property lines
• Height limits: typically 16–25 feet for detached ADUs
• Lot coverage: ADU typically cannot exceed 40–50% of remaining lot coverage allowance
• Some cities require ADU to share utility connections with main home

How Long Does an ADU Permit Take?

ADU permits take longer than most residential permits — typically 4–12 weeks depending on your city. Cities with high ADU volume (California, Oregon, Washington) have streamlined the process, but elsewhere it can be slow. A complete, accurate drawing package is the best way to avoid revision cycles.

Practical Permit Review Checklist

Before you submit your application, review the drawing as if you were the city plan reviewer. The plan should clearly show what already exists, what is being added, where the work will happen, and how the project fits within the property limits. For ADU permit requirements drawings, the most important details are usually the property boundaries, accurate dimensions, setbacks, north arrow, project address, parcel information, and clear labels for existing and proposed work. These details help the reviewer understand the scope quickly and reduce avoidable correction comments.

• Confirm that the project address and owner information are correct.
• Check that proposed work is labeled separately from existing structures.
• Make sure setback distances are easy to read.
• Use consistent measurements across the site plan, floor plan, and any supporting drawings.
• Attach the plan in the format requested by your local building department.

How to Prepare Your Project Details

A better starting package usually creates a better final drawing. Gather your property address, a short description of the work, photos of the project area, rough measurements, and any instructions from the permit office. If you already have an old survey, plot plan, contractor sketch, or HOA document, include it during the order process. Even when those files are not perfect, they give the drafting team useful context and help prevent missing information.

For homeowners, the goal is not to create a complicated architectural package. The goal is to give the building department a clear, scaled, and easy-to-review drawing. That is why ADU Permit Requirements: What Drawings Do You Need? should focus on accuracy, simple labels, and the specific details your jurisdiction asks for. A clean plan is often easier for the reviewer to approve than a crowded drawing with unnecessary notes.

Common Mistakes to Avoid

Many permit delays happen because small details are missing. Common issues include using screenshots instead of scaled drawings, leaving out setbacks, showing old structures that no longer exist, forgetting easements, or submitting a plan that does not match the permit application. Another common mistake is using a generic plan when the city requires project-specific information. A permit-ready drawing should match your address, your project, and your local review requirements.

Frequently Asked Questions