ADU Builder in Atherton, CA
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Atherton ADU Rules
Under Chapter 17.52, a single-family lot may have one ADU plus one JADU, and lots of 2 acres or more may add a deed-restricted bonus ADU.
- Size: new ADUs up to 1,200 sq ft; JADUs up to 500 sq ft; conversions of existing space have no size limit.
- Height: detached 16 feet (18 near transit); attached 25 feet or the zone limit.
- Setbacks: 4 feet side and rear for ADUs of 800 sq ft or less.
- Floor area: the first 800 sq ft of an ADU and up to 500 sq ft of a JADU do not count toward the home’s maximum.
- Parking: at most one space, and none in many cases.
- Rentals: longer than 30 days; no owner-occupancy requirement for units permitted since 2020.
Review is ministerial, with no hearing, and a decision within 60 days of a complete application.
ADU Construction
Building an ADU on an Atherton Estate
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.
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.
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
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Atherton ADU Builder FAQ
How large can an ADU be in Atherton?
Up to 1,200 sq ft for a new ADU; conversions of existing space have no size limit.
Does an ADU count toward floor area?
The first 800 sq ft of an ADU does not.
Is there a hearing?
No. ADU review is ministerial, decided within 60 days.
Can I build two ADUs?
One ADU plus one JADU, and lots of 2 acres or more may add a deed-restricted bonus ADU.