Home Additions in Palo Alto, CA
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Second Stories in Palo Alto
Two-story Objective Design Standards (effective February 14, 2025) apply to new two-story homes and second-story additions of 150 sq ft or more, unless you choose Individual Review. The second floor is capped at the larger of 35% of allowable floor area or 400 sq ft, and roof decks are not allowed. Under Individual Review, notice is mailed and posted to abutting, across-the-street and diagonal neighbors within 3 days, followed by a 21-day comment period; the Director’s decision becomes final after 14 days unless a hearing is requested.
Eichlers and single-story overlays: Palo Alto has 31 Eichler tracts built from 1949 to 1974, and Single-Story Overlay (SSO) districts covering 11 of them limit homes to one floor and 17 feet. Greenmeadow and Green Gables are National Register districts. Professorville (about 200 homes from the 1890s to 1930s) and Crescent Park, with its Birge Clark houses, add older stock that may trigger historic review for homes over 45 years old.
Addition Work
Addition Thresholds
- Fire sprinklers (Palo Alto local amendment): additions of 50% or more of existing area, fire areas over 3,600 sq ft, replacing 50% or more of roof or exterior walls, and new or expanded basements.
- School fees: additions of 500 sq ft or more pay Palo Alto Unified or Los Altos School District fees, with the receipt required before permit.
- Protected trees: native oaks, big-leaf maple and incense cedar at 11.5 inches diameter, coast redwood at 18 inches, and other mature trees at 15 inches. Plans need a T-1 tree protection sheet.
- Flood zones: lowest floor at base flood elevation plus 1 foot, which effectively rules out basements; dewatering only April 1 to October 31.
City of Palo Alto Utilities (CPAU): Palo Alto runs its own electric, gas, water and wastewater utility, and one utilities application goes in through Building. A service upgrade needs a load calculation, meter location and photos; CPAU engineering review can take up to 45 business days, and installation is scheduled after payment, often 30 to 40 business days later. We submit this early so it does not hold up your project.
285 Hamilton Avenue, Palo Alto, CA 94301 (next to City Hall at 250 Hamilton)
Building (650) 329-2496, Bu******@******to.gov · Planning (650) 329-2441
In-person counter Monday to Thursday, 8:30 a.m. to 12:30 p.m. and 1:30 to 4:30 p.m.; Friday service is virtual. Applications and payments go through Accela Citizen Access (ACA). Inspections are requested in ACA or the Palo Alto Inspection Request app; finals by phone at (650) 329-2496, option 2.
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Same service nearby: Mountain View · Los Altos · Los Altos Hills
Palo Alto Home Additions FAQ
Do second-story additions need review in Palo Alto?
Second-story additions of 150 sq ft or more follow the Objective Design Standards, or you can choose Individual Review with neighbor notice.
How big can the second floor be?
The larger of 35% of allowable floor area or 400 sq ft under the objective standards.
When does an addition need sprinklers?
When it adds 50% or more of existing area, among other triggers.
Can I add a second story in an Eichler tract?
Not in a Single-Story Overlay district.