ADU Builder in Hillsborough, CA
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Hillsborough ADU Paths
Under Chapter 17.52, Hillsborough offers three paths: State-Exempt, ADU Planning Permit and Exception. A State-Exempt ADU, either within an existing footprint or a new detached unit of 800 sq ft or less, 16 feet tall or less, with 4-foot side and rear setbacks, goes straight to building permit. JADUs are up to 500 sq ft with an efficiency kitchen, and the Town has a pre-approved plans gallery (ad*@**********gh.net).
An ADU must be sprinklered if the main house has, or is required to have, sprinklers.
ADU Construction
Building on an Estate Lot
Construction rules: work hours are 8 a.m. to 5 p.m. weekdays and 10 a.m. to 5 p.m. Saturdays, with no noisy work on Sundays or Town holidays. The construction impacts ordinance covers on-site parking, screening, neighbor notice and completion time limits, and larger projects need a pre-construction meeting and a qualified superintendent.
Trees: any tree 18 inches or more in diameter at 4½ feet is protected. Removals tied to development go through design review first, with an arborist report and replanting plan.
1600 Floribunda Avenue, Hillsborough, CA 94010 · Town Hall (650) 375-7400
Building (650) 375-7411, pl*******@**********gh.net · Planning (650) 375-7422 (planners by appointment) · Engineering (650) 375-7444
Applications are electronic through eTRAKiT, and contractors register with their CSLB license. Inspections are requested by phone at (650) 375-7411 at least two to three days ahead; inspectors will not inspect work by subcontractors who are not on the subcontractor list or lack a Town business license. Hours vary, so call ahead.
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Other Hillsborough services: Bathrooms · Kitchens · Additions · New Homes · Hillsborough overview
Same service nearby: Burlingame · San Mateo · Belmont
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Hillsborough ADU Builder FAQ
Can I skip design review for an ADU?
Yes. A State-Exempt ADU of 800 sq ft or less, 16 feet tall, with 4-foot setbacks goes straight to building permit.
Does the ADU need sprinklers?
If the main house has or requires them.
Are there pre-approved ADU plans?
Yes, in the Town’s gallery.
How large can a JADU be?
500 sq ft, with an efficiency kitchen.