ADU Engineering & Permits

We serve Northern California across three regions: the San Francisco Bay Area (six counties from Alameda to Santa Clara), Greater Sacramento (Sacramento out to Roseville, Folsom, and Davis), and the Central Valley (Stockton to Modesto). Our crews are based in Castro Valley. We handle permits and know the building codes for each jurisdiction, which matters because requirements and fees vary significantly between cities.

We offer $0-down financing with approved credit, 12-month same-as-cash plans, and extended terms up to 15 years for larger projects. You only pay for completed, inspected work — we never ask for full payment before the job is done. Your project manager will walk you through every option during your estimate appointment. We also accept checks, ACH, and all major credit cards.

Yes. CSLB License #1078806 — verify it anytime at cslb.ca.gov. We carry $2M general liability, full workers’ comp, and are bonded per California law. We hold GAF Master Elite, Owens Corning Preferred, CertainTeed ShingleMaster, and James Hardie Elite Preferred certifications — each requires annual training and quality audits to maintain. We’re happy to provide proof of insurance before any work begins.

Most exterior projects in Northern California require a building permit. Fees vary by city — Oakland runs $200–$600, Peninsula cities often more. We handle the entire permit process: application, plan submission, and scheduling inspections. Permit fees appear as a separate line item in your estimate so you’ll see every cost upfront. For homes in WUI fire zones (Berkeley Hills, Oakland Hills, parts of Marin), we ensure full compliance with local fire-rated material requirements.

Timelines vary by city. Oakland averages four to six weeks, San Jose three to five weeks, Berkeley six to eight weeks, and Palo Alto five to seven weeks. California law requires cities to act on complete ADU applications within 60 days. Our permit packages are designed for first-submission approval to avoid delays from resubmissions.

We guarantee your complete ADU permit package will be submitted within 60 days of design sign-off. If plan check corrections are required, we cover all resubmission costs at no additional charge. This guarantee applies to standard ADU projects in our Bay Area service area.

Yes. ADUs require a building permit from your local jurisdiction. However, under California state law (AB 2221), ADU permits are approved ministerially, meaning without discretionary review or public hearings, as long as the project meets zoning and building code requirements. This is significantly faster than the traditional planning approval process.

A complete package includes architectural plans, structural engineering with seismic calculations, Title 24 energy compliance, CalGreen checklist, MEP plans, fire sprinkler layout, and soils reports when required. We also prepare the permit application forms, fee calculations, and school district impact fee documentation.

Permit fees vary by city and ADU size. Plan check and building permit fees typically range from $5,000 to $15,000. School impact fees add $3,600 to $6,300 for a 750-square-foot unit depending on the district. Utility connection fees, if required, range from $2,000 to $8,000. We calculate all fees during the feasibility phase for accurate budgeting.

California state law allows a minimum four-foot side and rear setback for detached ADUs, overriding stricter local codes. Garage conversions can maintain their existing setback even if it is less than four feet. Front setbacks follow local zoning, typically 15 to 20 feet. Our architects verify the specific rules for your property during the feasibility study.

Most Bay Area jurisdictions require fire sprinklers in new ADU construction, consistent with the California Residential Code. The requirement applies to new detached and attached ADUs but typically does not apply to garage conversions under certain conditions. Sprinkler systems add approximately $3 to $5 per square foot to construction costs.

Title 24 is California's energy efficiency standard for buildings. For ADUs, it requires high-performance insulation, efficient HVAC (typically heat pumps), low-E windows, LED lighting, and solar-ready roofing. Our energy consultants run compliance models and produce the required CF-1R registration forms as part of every permit package.

California law (AB 2221) prohibits HOAs from outright banning ADUs on single-family lots. However, HOAs can impose reasonable design standards related to aesthetics, such as exterior materials and colors. Our architects design ADUs that comply with both local building codes and HOA design guidelines.

Soils and geotechnical reports are required when building on slopes exceeding 10 percent, in liquefaction zones, or on expansive clay soils common in parts of Fremont, San Jose, and Hayward. Even when not required, we recommend soils testing for foundation design accuracy. Reports typically cost $2,500 to $4,000.

Plan check corrections are comments from the building department requesting changes or clarifications to the submitted plans. We respond to corrections within five business days, revise the plans, and resubmit. Under our 60-day permit guarantee, all correction and resubmission costs are covered by Hamilton Exteriors.

No. Garage conversions require building permits, structural engineering (to verify the existing structure meets residential occupancy requirements), and compliance with Title 24 energy standards. However, garage conversion permits are typically faster and less expensive than new construction permits because the existing structure reduces the scope of review.

SB 9 (California Housing Opportunity and More Efficiency Act) allows lot splits and duplex development on single-family lots, which can be combined with ADU provisions to increase density. A property could potentially have a primary home, an ADU, a JADU, and an SB 9 duplex unit. Our team evaluates how SB 9 and ADU laws interact for your specific property.

Under California law, cities cannot require separate utility connections for ADUs on the same lot as the primary dwelling. However, you may choose separate meters for tenant billing. Electrical panel upgrades from 100-amp to 200-amp service are common. We coordinate with EBMUD, Cal Water, and PG&E for all utility requirements.