ADU plan check corrections

ADU plans get reviewed like a small house, so the correction letters tend to be long. Most comments fall into a few groups: fire separation, egress and alarms, utilities, energy, and structure. Here's what each one asks for and how to answer it.

Updated October 24, 2026 · By the Plan Check Correct team · General information, not legal or engineering advice. Requirements vary by jurisdiction.

Site plan and zoning

• "Show setbacks from the ADU to all property lines."Dimension the ADU to each property line and show the required setback lines. In California, a city can't require more than 4 feet from the side and rear lot lines for an ADU.
• "Show the distance between the ADU and the main house."Dimension the closest points, including eaves and other projections. This affects fire separation as well as zoning.
• "Show the ADU's floor area and height."Add the conditioned square footage, any lot coverage or floor area figures your zoning uses, and the building height on the elevations.
• "Show the address and access to the ADU."Show the address numbers for the ADU, visible from the street (IRC R319), and the path from the street to its entrance. Some fire departments set a minimum width for that path.
• "Show utilities and easements."Show the meters, panels, sewer lateral or septic system, and any easements the ADU must stay out of.

The free site plan maker draws the ADU, main house, setbacks and distances to scale.

Fire separation

• "Show fire-resistance-rated exterior walls near property lines."Under the IRC, exterior walls less than 5 feet from a property line generally need a 1-hour rating, openings aren't allowed within 3 feet, and openings between 3 and 5 feet are limited to 25% of the wall area (Table R302.1(1)). With fire sprinklers, the limits drop to 3 feet. An ADU built at a 4-foot setback usually needs a rated wall. Show the rated assembly, its listing number and the eave construction.
• "Show the dwelling unit separation."An attached ADU, or one above a garage, needs a fire-resistance-rated wall or floor between the units: 1-hour, or ½-hour with fire sprinklers (IRC R302.3). Show the assembly and that it continues to the roof sheathing or foundation.
• "Show the garage separation."Living space next to or above a garage needs gypsum board separation, with 5/8-inch Type X under living space above (IRC R302.6). A door between the garage and living space must be solid wood or steel at least 1-3/8 inches thick, or 20-minute rated, and self-closing (IRC R302.5.1). California also requires it to be self-latching. No door can open from a garage directly into a sleeping room.
• "Show wildfire-resistant construction."In a wildland-urban interface or fire hazard zone, show ignition-resistant materials, ember-resistant vents and the required roof class (CRC R337 in California).

Egress, alarms and habitability

• "Show emergency escape and rescue openings."Each sleeping room needs an egress window or door with at least 5.7 square feet of net clear opening (5.0 at grade level), at least 24 inches high and 20 inches wide, and a sill no higher than 44 inches (IRC R310). Put the sizes in the window schedule.
• "Provide smoke and carbon monoxide alarms."Show smoke alarms in each bedroom, outside sleeping areas and on each level, and CO alarms where there are fuel-burning appliances or an attached garage (IRC R314 and R315). Many departments also ask for alarms in the main house when an ADU is added.
• "Show ceiling heights."Habitable rooms generally need at least a 7-foot ceiling (IRC R305). This often comes up in garage and basement conversions.
• "Show the kitchen and bathroom."An ADU needs permanent facilities for living, sleeping, eating, cooking and sanitation. Show the cooking appliance, sink, counter and refrigerator space, and the bathroom fixtures and exhaust fan.
• "Show natural light and ventilation."Show window areas for habitable rooms, or mechanical ventilation where windows don't meet the code (IRC R303).

Garage conversions

• "Show the floor build-up."Garage slabs are often below the house floor and sloped toward the door. Show the moisture barrier, insulation, sleepers or new floor framing, and the finished floor height.
• "Detail the garage door infill."Show the new wall framing, its footing or curb, how it ties to the existing structure and any shear wall that replaces the garage door opening.
• "Show the energy upgrades."A converted garage becomes new conditioned space, so show insulation for the walls, ceiling and floor and the heating and cooling, with your state's energy compliance forms.
• "Show replacement parking."In California, a city can't require you to replace parking lost when a garage is converted to an ADU. If you get this comment, ask the reviewer to confirm it given state ADU law.
• "Show the existing structure meets current setbacks."In California, converting an existing garage or accessory building, or rebuilding it in the same place and size, doesn't trigger new setbacks. Note that the structure is existing and isn't being enlarged.

Utilities

• "Provide an electrical load calculation."Show that the existing service can carry the house plus the ADU (NEC Article 220), or show the service upgrade. Size the feeder to the ADU's subpanel.
• "Show water and sewer sizing."Show the added fixture units, the water service and meter size, the sewer connection with cleanouts, or the septic system's capacity if you're on septic.
• "Show gas pipe sizing."If the ADU has gas appliances, show the pipe sizing for the total connected load from the meter.
• "Show the water heater and HVAC."Show the equipment, its location and clearances, and the load calculation for the heating and cooling equipment (IRC M1401.3).

Energy

• "Provide energy compliance documentation."Attach the energy compliance forms (in California, the Title 24 CF1R) and copy the required measures onto the plans, including any items that need third-party HERS verification.
• "Show the solar PV system."In California, new detached ADUs are generally treated as new homes under the Energy Code, which can require a solar PV system unless an exception applies. Attached ADUs and conversions are generally treated as additions or alterations, but the building department decides. Check which applies to yours and show the system or the exception on the plans.

Structure

• "Provide foundation design."Show footing sizes and reinforcing. Hillside lots, expansive soils and some cities call for a soils report.
• "Show lateral bracing."Show braced wall lines and panels (IRC R602.10), or the engineer's shear wall design with hold-downs and nailing.
• "Provide structural calculations."Beams, headers and point loads beyond the IRC's prescriptive tables, ADUs above garages, and second-story additions usually need an engineer's calculations.
• "Show the prefab unit's approval and anchorage."For a factory-built ADU, attach the state approval or insignia information and show the foundation and anchorage design.

California rules that limit what a city can require

State ADU law (Government Code section 66314 and the sections after it) overrides many local rules. A few that come up in plan check:

• When there's already a home on the lot, the city must approve or deny a complete ADU application within 60 days, or it's deemed approved.
• If it denies the application, it must give you a full set of comments listing the deficient items and how to fix them.
• Side and rear setbacks can't be more than 4 feet, and no new setback applies to converting an existing structure.
• Fire sprinklers can't be required in an ADU if they aren't required for the main house.
• Replacement parking can't be required when a garage is converted to an ADU.

HCD's ADU Handbook explains these rules in plain language. If a comment seems to conflict with them, raise it politely with the reviewer and cite the section.

Frequently asked questions

Sources

• California Government Code section 66314 (ADU standards: setbacks, sprinklers, parking)
• California Government Code section 66317 (60-day review and denial comments)
• California Department of Housing and Community Development: Accessory Dwelling Units
• California Energy Commission: 2022 Energy Code, general information on ADUs
• International Code Council: 2021 International Residential Code