During the construction of an Accessory Dwelling Unit (ADU), inspections play a vital role in ensuring the structure meets building codes, safety standards, and local regulations. Each required inspection helps verify that every stage of construction is completed correctly, safely, and according to approved plans.

From foundation and framing to plumbing, electrical, insulation, and the final inspection, these checkpoints are essential in determining the structural integrity and readiness of the ADU for occupancy.

This article provides a clear, in-depth overview of all inspections involved in ADU construction and what homeowners should expect throughout the process.

Overview of ADU Construction Inspections

Building an ADU involves a series of scheduled inspections designed to ensure safety, regulatory compliance, and construction quality.

Why Inspections Matter

Inspections help prevent construction errors, verify that materials and construction methods meet building standards, and ensure long-term durability. They also protect homeowners from potential safety issues and costly repairs down the line.

Regulatory Requirements

Local building departments require inspections at specific milestones. These requirements ensure that your ADU meets all applicable codes, zoning rules, and design standards before it can be legally occupied.

Foundation and Footing Inspection

The foundation serves as the structural base for the entire ADU, making this one of the most important inspections during the project.

Preparing for the Foundation Inspection

Before the inspection, all excavation, forms, reinforcements, and utilities beneath the slab must be in place. The site must be clean, accessible, and ready for review.

What Inspectors Look For

• Proper depth and width of footings

• Adequate rebar placement

• Correct concrete forms

• Soil conditions and compaction

• Compliance with structural plans

This inspection ensures the foundation is strong enough to safely support the ADU.

Framing and Structural Inspection

Once walls, floors, and the roof structure are built, a framing inspection confirms that the ADU’s “skeleton” is properly assembled.

Key Items Checked

• Wall alignment, spacing, and structural connections

• Roof framing and truss installation

• Load-bearing components

• Window and door openings

• Compliance with engineering and architectural plans

Structural Integrity Review

Inspectors verify that framing is structurally sound, capable of supporting loads, and aligned with code requirements for wind, seismic forces, and durability.

Plumbing and Electrical Inspection

These systems ensure the ADU is safe, functional, and comfortable for everyday living.

Plumbing Inspection

Inspectors check for:

• Proper pipe installation

• Adequate drainage and venting

• Leak-free connections

• Approved materials and fixture placement

Pressure tests are commonly performed to confirm system integrity.

Electrical Inspection

The electrical inspection covers:

• Correct wiring installation

• Proper grounding

• Code-compliant placement of outlets and switches

• Safe panel installation

• Proper circuit protection

These checks prevent electrical hazards and ensure safe long-term operation.

Insulation and Drywall Inspection

Insulation Inspection

Before drywall is installed, inspectors verify:

• Correct insulation type and R-values

• Proper installation without gaps or compression

• Vapor barriers where required

This step ensures energy efficiency, comfort, and adherence to state energy codes.

Drywall Inspection

After drywall installation but before finishing:

• Screw/nail spacing

• Fire-rated assemblies

• Proper seams and backing

• Overall installation quality

This step ensures walls and ceilings are structurally sound and ready for finishing.

Final Inspection and Certificate of Occupancy

Preparing for the Final Inspection

The ADU must be 100% complete, including:

• Fixtures

• Finishes

• Railings

• Smoke and CO detectors

• Exterior grading and drainage

• All permits and inspection sign-offs

Certificate of Occupancy (CO)

Once the final inspection is passed, the city or town issues a Certificate of Occupancy, confirming that the ADU is safe, code-compliant, and legally ready for use.

Additional Inspections in ADU Construction

Some ADUs may require specialized inspections depending on features such as:

• HVAC systems

• Fire sprinklers (if required)

• Solar installations

• Accessibility requirements

Zoning Compliance Checks

In many areas, inspectors or zoning officials will verify:

• Setbacks

• Height limits

• Lot coverage

• Parking requirements

Staying compliant avoids delays, fines, or required modifications.

Importance of Following Inspection Requirements

Every inspection ensures your ADU is built safely, responsibly, and legally. Catching issues early prevents costly rework, delays, and safety hazards later on. By completing each required inspection, homeowners protect their investment and ensure the ADU will be comfortable, durable, and code-compliant for years to come.

Conclusion

Successfully navigating the ADU inspection process is essential to building a safe and compliant structure. By understanding and preparing for each inspection—from foundation to final—you can avoid setbacks, reduce costs, and ensure your ADU is built to the highest standards.

A thorough inspection process not only guarantees code compliance but also gives homeowners confidence that their ADU is ready for long-term use, whether as a rental, guest suite, or extended family space.

FAQ

What if my ADU fails an inspection?
You will receive a correction notice. After addressing the issues, you can request a reinspection. Delays are common, but resolving issues promptly helps keep the project on schedule.

Can I schedule inspections at different stages?
Yes. Inspections must be scheduled at designated milestones such as foundation, framing, plumbing, electrical, insulation, and final inspection.

Do inspection requirements vary by location?
Yes. Every municipality has its own building and zoning regulations. Always review your local building department’s requirements.

How long does it take to get the Certificate of Occupancy?
Typically a few days to two weeks after the final inspection, depending on the local building department’s processing times.