Every newly constructed detached ADU in San Mateo County, California must include a Title 24-compliant solar PV system. San Mateo County spans climate zone 3, which determines exactly how many kilowatts your specific project must install for code compliance.
Local building departments across San Mateo County enforce Title 24 at plan check. Plans submitted without a properly sized solar system are routinely rejected unless a documented exemption (shading, roof area, structural) applies.
San Mateo County's extreme housing costs make ADU construction a high-value investment. Peninsula Clean Energy provides 100% clean electricity, complementing solar ADU installations.
Title 24 multiplies your ADU's conditioned floor area by a climate-zone-specific kW factor. Across San Mateo County's climate zone 3, most ADUs land in the 1.6–4.0 kW range — typically 4 to 10 modern (~400W) panels.
Title 24-compliant ADU solar packages range from $4,000 (Standard cash) to $15,000+ (Premium with battery) across San Mateo County. HDM financing typically reduces effective cost by ~40% via commercial ITC pass-through. Main utilities serving the county: PG&E, PCE.
Yes. Title 24 is California state law and every jurisdiction in San Mateo County enforces it at permit submittal.
San Mateo County sits in climate zone 3. Use our cost calculator to map your exact ZIP code to its Title 24 climate zone.
Exemptions are project-specific, not countywide. The most common are shading (<70% annual solar access), insufficient roof area, and structural infeasibility. Your designer documents these on the CF1R compliance form.