Home Additions in Atherton, CA
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Atherton Zoning for Additions
R-1A standards: new lots are 1 acre on flatter land, 2 acres at 20% to 35% slope and 5 acres above that. Floor area is 18% of lot area on lots of an acre or more, with floor area above the first floor capped at 7.5% of the lot. Height is 30 feet (22-foot sidewalls), up to 34 feet with larger setbacks or a Special Structures Permit, measured from average natural grade. Front and rear setbacks are 60 feet. Basements stay within the first-floor footprint, up to 100% of first-floor area, or 120% with a Special Structures Permit.
There is no single-family design review listed in the Town’s approval table; the town planner checks compliance with the standards, and the Planning Commission hears Special Structures Permits, variances and heritage tree removals, with notice mailed within 500 feet at least 10 days ahead.
Addition Work
Trees, Hours and Permit Limits
Heritage trees: a tree is protected at 48 inches in circumference (about 15 inches diameter) at 54 inches above grade. Native oaks qualify anywhere on the lot; other species qualify outside the main buildable area. Staff can approve removal of dead or dangerous trees; other removals go to the Planning Commission, and a heritage oak removed from the buildable area is replaced with a 48-inch box oak.
Construction hours: construction, pickups and deliveries are allowed only 8 a.m. to 5 p.m., Monday to Friday, with no contractor work on Saturdays, Sundays or Town holidays. Construction vehicles cannot arrive before 8 a.m., must leave by 5 p.m., and must turn engines off while loading.
Permit time limits: 12 months for projects of 2,000 sq ft or less, 24 months up to 4,000 sq ft, and 36 months above that. We schedule to stay inside these limits.
Permits and plan check go through the Town Building Department at Town Hall; call the Town to confirm current counter hours before visiting.
Fire: Menlo Park Fire Protection District, Fire Prevention, 170 Middlefield Road, Menlo Park, (650) 688-8400 · Sewer: West Bay Sanitary District, 500 Laurel Street, Menlo Park, (650) 321-0384.
A Construction, Operation and Parking (COP) plan must be approved by the Building Official before plans go to plan check.
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Same service nearby: Menlo Park · Palo Alto · Los Altos Hills
Atherton Home Additions FAQ
How much floor area can I add in Atherton?
Up to 18% of lot area on lots of an acre or more, with upper floors capped at 7.5% of the lot.
Is there design review?
No single-family design review is listed; staff checks compliance with the standards.
How tall can an addition be?
30 feet, or up to 34 feet with larger setbacks or a Special Structures Permit.
Are trees protected?
Heritage trees 48 inches in circumference or more at 54 inches.