Atherton staff outline streamlined process to legalize accessory dwelling units

Town planners and the building official described a streamlined path for Atherton homeowners to create and legalize accessory dwelling units, saying the changes make ADUs a practical way to add smaller, often more-affordable housing while preserving neighborhood character.

Jerry Martin, assistant planner for the town, defined an ADU as “a secondary residential unit on the same lot as a primary home” with its own kitchen, bathroom, sleeping area and separate entrance. He and other staff stressed that ADUs can count toward the town’s housing-element targets certified last year by the California Department of Housing and Community Development (HCD).

Fred Lenberger, Atherton’s building official, said the town’s legalization approach emphasizes safety rather than forcing full compliance with new-construction standards. “We’re looking at basically the bare minimum to make the space compliant and safe,” he said, listing checks for inadequate sanitation, structural hazards, fire protection and electrical and plumbing safety.

Staff outlined two common state-aligned pathways: converting existing legal space (for example, a garage, guest house or underused interior area) and legalizing previously unpermitted units. They said state law now constrains many local limits—on setbacks, heights and floor-area rules—for conversion and legalization projects.

On process, Lenberger described these practical steps: meet with planning/building staff for a pre-application review, provide site documentation and plans (energy calculations and basic drawings), submit a permit application at the building counter, undergo plan-check cycles, complete the work and receive inspections and final approval. He noted that building permits for these ADU legalizations are issued without a building-side permit fee. “I should mention the permit’s free,” Lenberger said.

Staff gave several size and setback thresholds homeowners should know: junior ADUs (JADUs) are limited to 500 square feet and are inside a residence; a common state threshold is 800 square feet—ADUs 800 sq ft or smaller are subject to certain state exemptions (for example, limited local review on tree rules). ADUs above 800 sq ft face additional local requirements; staff noted a 1,200-square-foot reference for front-setback rules in some cases and reiterated a typical 10-foot separation from the main house unless mitigated by firewall construction.

On utilities and sewer, staff said the town is coordinating with local sewer districts to charge for ADU sewer use by fixture capacity rather than treating every ADU as a full additional unit. Electrical service may require a separate meter in many cases; addressing often uses the primary address with an “A” suffix for the ADU.

In the public Q&A, a resident asked whether a front-yard ADU is allowed; staff replied that detached or attached ADUs of 800 square feet or less can be sited in front yards under state rules, subject to side and rear setbacks (commonly four feet). Another question on SB9 lot splits drew the staff response that Atherton has adopted an SB9 ordinance; after a split, jurisdictions typically allow up to two units on a lot (an existing house plus one ADU).

Staff estimated plan-review pacing at about 10 business days per building review cycle; if plans are complete they could be approved in as little as two weeks, but two-to-three review cycles make a realistic timeline closer to four to five weeks. Prefabricated ADUs follow the same planning and building rules, staff said, with logistics (crane access, foundation) being the main practical differences.

For homeowners considering conversion or legalization, staff pointed to online handouts, state and regional ADU guides and the town’s permit checklist and encouraged pre-site meetings so planners and building staff can identify likely hurdles and inspection needs. The presentation closed with several resident questions about specific conversions (for example, precedent gardener cottages), and staff said minor corrections—handrails, stair repairs—are typically manageable as part of legalization rather than requiring full reconstruction.

The workshop did not include any motions or formal votes; staff said next steps are individual pre-application consultations and standard permit submittals for homeowners who want to proceed.