What Comments Do Plan Checkers Usually Flag on ADU ...

The Most Common ADU Plan Check Corrections and How to Avoid Them

Every ADU plan submission goes through a detailed review process where plan checkers examine your construction documents for compliance with California's building codes, local zoning ordinances, and various other requirements. When the plan checker finds issues, they issue "corrections" or "comments" that must be addressed before your permit can be issued.

Understanding what plan checkers commonly flag allows you to address these issues in your original submission, potentially avoiding one or more rounds of corrections and saving weeks or months on your plan check timeline. We have reviewed hundreds of plan check correction letters from building departments across California and compiled the most frequently flagged items in this guide.

Whether you are an architect preparing ADU plans, a homeowner reviewing your designer's work, or a contractor managing the permit process, this guide will help you understand what plan checkers are looking for and how to submit plans that pass review with minimal corrections.

Structural and Engineering Comments

Structural issues are among the most common and most consequential plan check corrections. Plan checkers take structural safety very seriously, and incomplete or incorrect structural information will always be flagged.

1. Missing or Incomplete Structural Calculations

This is the single most common structural correction. Plan checkers require complete structural calculations that show how the building will resist gravity loads (dead and live loads) and lateral loads (wind and seismic forces). Common deficiencies include:

• Missing lateral force analysis (seismic and wind calculations)
• Incomplete load path analysis (showing how loads transfer from roof to foundation)
• Missing or inadequate foundation calculations
• Incomplete connection details (hold-downs, straps, bolting patterns)
• Missing wood species and grade specifications

How to avoid it: Hire a licensed structural engineer to prepare complete calculations. Do not rely on a designer or architect to provide structural engineering unless they are also a licensed structural engineer.

2. Inadequate Shear Wall Layout

Shear walls resist lateral forces (earthquake and wind). Plan checkers frequently flag shear wall layouts that do not provide adequate bracing in both directions or that have insufficient length relative to the building dimensions. This is particularly common in ADUs with large window openings or open floor plans.

How to avoid it: Your structural engineer should provide a shear wall schedule showing the exact location, length, nailing pattern, and sheathing requirements for every shear wall panel. The shear walls must be balanced on both axes of the building.

3. Foundation Details

Foundation corrections commonly involve insufficient footing depth, missing rebar specifications, inadequate anchor bolt spacing, or foundation details that do not match the geotechnical report recommendations. If a soils report recommends specific foundation types or depths, the structural plans must reflect those recommendations.

Zoning and Site Plan Comments

Zoning corrections relate to how your ADU complies with local zoning regulations. These are often the easiest corrections to avoid by carefully reviewing your city's ADU ordinance before preparing plans.

4. Setback Violations

Setback corrections are extremely common, especially for homeowners unfamiliar with California's ADU setback rules. Under state law, detached ADUs may be placed with a 4-foot minimum setback from the side and rear property lines. However, some local jurisdictions require greater setbacks for certain ADU types or in specific zones.

Common setback issues include:

• ADU located too close to a property line
• Eave, gutter, or roof overhang encroaching into the required setback
• Stairs, porches, or decks not included in setback measurement
• Using the wrong setback requirement (main house setbacks vs. ADU-specific setbacks)

How to avoid it: Obtain a current property survey and accurately dimension the ADU's distance from all property lines. Remember that setbacks are measured from the closest point of the structure, which may be an eave overhang rather than the wall face.

5. Height Violations

ADU height limits have been revised by recent state legislation, and some plan checkers may not be fully up to date on the current rules. However, more commonly, the issue is that the plans do not clearly show how the building height is measured (from natural grade, finished grade, or some other reference point).

How to avoid it: Clearly dimension the building height on your elevations, referencing the correct measurement point per your local code. Include the natural grade and finished grade at all corners of the ADU.

6. Lot Coverage Calculations

Many jurisdictions limit total lot coverage (the percentage of the lot covered by structures). Adding an ADU increases lot coverage, and plan checkers will verify that the total does not exceed the allowed maximum. A common error is failing to include covered patios, decks, and accessory structures in the lot coverage calculation.

7. Parking Requirements

While California state law has eliminated parking requirements for most ADUs (particularly those within half a mile of transit), some jurisdictions still require parking in certain circumstances. Plan checkers will verify that any required parking spaces meet dimensional standards and are properly shown on the site plan.

Building Code Compliance Comments

8. Egress Window Requirements

Every sleeping room in an ADU must have an emergency escape and rescue opening (egress window) that meets specific size requirements. The window must have a minimum net clear opening of 5.7 square feet, with a minimum opening height of 24 inches and a minimum opening width of 20 inches. The sill height cannot exceed 44 inches above the finished floor.

This is one of the most frequently flagged items because many designers specify windows that look right but do not meet the net clear opening requirement. The "net clear opening" is the actual unobstructed opening when the window is fully open, which is smaller than the window's overall dimensions.

How to avoid it: Specify the exact window model and include the manufacturer's egress certification data on the plans. Mark each sleeping room's egress window clearly on both the floor plan and the window schedule.

9. Smoke and CO Detector Requirements

California requires hardwired, interconnected smoke detectors in every sleeping room, outside each sleeping area, and on every floor. Carbon monoxide (CO) detectors are required outside each sleeping area and on every floor with a fuel-burning appliance or an attached garage. Plan checkers frequently flag plans that do not show detector locations or that show detectors in incorrect locations.

10. Kitchen and Bathroom Ventilation

The California Mechanical Code requires exhaust ventilation in all kitchens and bathrooms. Kitchen range hoods must exhaust to the exterior (not recirculating) unless specific exceptions apply. Bathroom exhaust fans must also vent to the exterior, not into the attic or crawl space. Plan checkers will look for ventilation ducting paths on the plans.

11. Fire Sprinkler Requirements

Whether your ADU requires fire sprinklers depends on its size, distance from property lines, and local ordinance. Under California law, ADUs are generally not required to have fire sprinklers if the main dwelling does not have them. However, there are exceptions, and plan checkers will verify compliance with the applicable fire sprinkler requirements.

Energy Code (Title 24) Comments

12. Incomplete Title 24 Documentation

Title 24 compliance documentation is required for all new ADU construction. Plan checkers commonly flag submissions where the Title 24 report is missing, incomplete, or does not match the construction documents. Common issues include:

• Window specifications on plans do not match the Title 24 model
• Insulation R-values on plans differ from the Title 24 calculations
• HVAC equipment efficiency ratings not specified or not meeting minimum requirements
• Missing solar-ready or solar zone requirements (for applicable projects)
• Water heater efficiency not meeting Title 24 requirements

How to avoid it: Hire an experienced Title 24 consultant and ensure that your architect or designer coordinates directly with the Title 24 consultant so that the construction documents and the Title 24 report are consistent.

Plumbing and Utility Comments

13. Sewer Connection Details

Plan checkers frequently flag missing or inadequate sewer connection details. Your plans should clearly show how the ADU's plumbing connects to the existing sewer system, including pipe sizes, slopes, cleanout locations, and connection points. If the ADU requires a new sewer lateral, the details of that connection must be shown.

14. Water Service Details

Whether the ADU shares the main house's water service or has a separate meter, the plans must clearly show the water supply routing, pipe sizes, and any required backflow prevention devices. If a separate meter is required, the meter location and service routing must be shown.

15. Gas Service (If Applicable)

For ADUs with gas service, plans must show the gas line routing from the meter to the ADU, pipe sizing calculations, and the location of a gas shutoff valve accessible from outside the ADU. If the ADU is all-electric, the plans should clearly state this to avoid gas-related corrections.

Drainage and Grading Comments

16. Inadequate Drainage Plan

As discussed in our drainage and grading guide, plan checkers pay close attention to how your project manages stormwater. Common drainage corrections include:

• Missing or incomplete drainage plan
• Inadequate slope away from the foundation
• No demonstration of LID (Low Impact Development) compliance
• Missing erosion control plan for grading work
• Unclear discharge location for collected drainage

How to Respond to Plan Check Comments Effectively

When you receive corrections, how you respond directly affects how quickly your plans are re-approved. Follow these best practices:

1. Create a correction response letter: Address each comment individually, citing the specific comment number and providing your response. State what was changed, what drawing sheet was revised, and reference the relevant code section if applicable.
2. Use revision clouds: Mark all changes on the revised plans with revision clouds (triangular or cloud-shaped markings around the changed areas). This allows the plan checker to quickly locate and verify your revisions.
3. Do not argue unless you are certain: If you disagree with a correction, you can respectfully challenge it by citing the specific code section that supports your position. However, this should be done carefully and only when you are confident in your interpretation. Arguing incorrect positions wastes time and can create adversarial dynamics with the plan checker.
4. Request a meeting for complex issues: If a correction is unclear or involves a complex technical issue, request a meeting with the plan checker to discuss it in person. This can resolve misunderstandings quickly and avoid multiple rounds of written corrections.
5. Resubmit promptly: Speed of response directly impacts your total timeline. Aim to resubmit corrections within 5 to 10 business days.

Pre-Submission Checklist to Minimize Corrections

Before submitting your ADU plans, review this checklist to catch common issues:

• All dimensions are shown on floor plans, elevations, and site plan
• Setbacks are clearly dimensioned from property lines to building (including eaves)
• Building height is dimensioned from the correct reference point
• Structural calculations are complete and signed by a licensed engineer
• Title 24 energy report is included and matches the construction documents
• Egress windows are specified with manufacturer data showing compliance
• Smoke and CO detector locations are shown on the electrical plan
• Kitchen and bathroom exhaust ventilation paths are shown
• Plumbing connection details (sewer, water, gas) are clearly shown
• Drainage plan is included with grading information
• All required reports are included (geotechnical, Title 24, etc.)
• All fees are paid at time of submission

Clean Plans Mean Faster Permits

The single best strategy for speeding up your ADU permitting process is submitting clean, complete plans that address every requirement on the first submission. While no set of plans is guaranteed to pass without any corrections, understanding what plan checkers commonly flag allows you to proactively address these issues in your design.

Work with an experienced ADU architect and structural engineer who regularly submit plans to your specific building department. Their familiarity with the local plan checkers' expectations is invaluable. The modest premium you pay for an experienced professional is quickly recovered in faster plan check times and fewer rounds of corrections.

Remember: plan check corrections are not personal. Plan checkers are doing their job to ensure your ADU is safe, code-compliant, and properly designed. Approach the process with professionalism and thoroughness, and you will get through it as efficiently as possible.

Pre-Submission Checklist: Items to Verify Before Submitting ADU Plans

Before you submit your ADU plans to the building department, review this checklist to minimize the chance of receiving plan checker corrections. Addressing these items upfront can save you weeks of back-and-forth during the plan check process.

Site Plan Checklist

• Property boundaries clearly shown with dimensions
• All existing structures labeled with distances to property lines
• Proposed ADU location with required setbacks noted
• Driveway, parking spaces, and access paths indicated
• Utility connections (water, sewer, gas, electric) marked
• Existing and proposed grading and drainage patterns shown

Architectural Plan Checklist

• Floor plan with room dimensions and labels
• All windows and doors sized and labeled with egress compliance
• Ceiling heights noted (minimum 7 feet for habitable rooms)
• Minimum bedroom dimensions verified (70 square feet minimum)
• Kitchen and bathroom layouts with fixture locations
• Accessibility requirements addressed if applicable

Structural and Mechanical Checklist

• Foundation type and specifications clearly detailed
• Framing details including connection hardware
• Roof framing plan with load calculations
• HVAC system design with duct layout
• Plumbing riser diagram and fixture schedule
• Electrical panel size and circuit layout
• Title 24 energy compliance forms completed

Frequently Asked Questions About Plan Checker Comments

How many rounds of plan check corrections are typical for an ADU?

Most ADU applications in California go through two to three rounds of plan check before receiving approval. The first round typically catches the most significant issues, while subsequent rounds address smaller details. Working with an experienced ADU designer or builder who understands local requirements can often reduce this to one or two rounds.

Can I speak directly with the plan checker about their comments?

Yes, most California building departments allow applicants or their representatives to schedule counter appointments with plan checkers. This face-to-face interaction can clarify ambiguous comments and help you understand exactly what corrections are needed. Some jurisdictions also offer virtual meetings or phone consultations.

What happens if I disagree with a plan checker's comment?

If you believe a plan checker has applied a code requirement incorrectly, you can request a meeting with a senior plan checker or building official. Bring your code reference and supporting documentation. In some cases, you may need to file a formal appeal. Having a licensed architect or engineer support your position strengthens your case significantly.

Do plan checker comments differ between cities in California?

Yes, while California building code provides the baseline, each city may have additional local amendments, zoning overlays, or specific submittal requirements. For example, Los Angeles plan checkers may flag items related to hillside grading that would not apply in flat valley cities. Always check your local jurisdiction's specific ADU guidelines before submitting.

Should I hire a plan check expediter for my ADU application?

A plan check expediter can be valuable if you are unfamiliar with the process or if your project is time-sensitive. Expediters typically charge $500 to $2,000 and can navigate the system efficiently, track your application status, and coordinate responses to plan checker comments. For straightforward ADU projects, many homeowners handle the process themselves with guidance from their designer or general contractor.