San Dimas Council approves two‑lot subdivision at 1356 West Sienega despite neighbor opposition

The San Dimas City Council voted 4–1 on May 12 to approve a tentative parcel map (25‑02) that will subdivide 1356 West Sienega Avenue into two lots for two new two‑story single‑family homes with attached two‑car garages and detached accessory dwelling units (ADUs).

The project was introduced by city planning staff as an in‑fill residential subdivision on a 17,274‑square‑foot property; staff said the proposal complies with objective development standards and noted the plan would remove a mature pine and a crepe myrtle and replace them with two 24‑inch‑box California sycamores per the city’s tree replacement rules. Planning staff also said the ADUs are shown for context but are permitted by state law and not subject to discretionary review.

Neighbors who live on the adjoining private street, Kimberley Avenue, told the council they feared increased traffic, parking spillover, reduced privacy from two‑story construction and long‑term consequences on a street that the city does not maintain. Several speakers described long‑running pavement and maintenance problems on the private roadway and asked the council to deny or delay the split until enforceable protections were in place.

The applicant spoke in support of the project, saying the existing house is more than 50 years old and that the proposed replacement would add housing stock and had been revised to provide additional on‑site parking and landscaping in response to community feedback.

Planning staff explained the council’s discretionary powers are constrained by state housing statutes (the presentation referenced the state 'Housing Crisis' provisions), which require cities to apply objective standards for certain small multi‑unit subdivisions. Staff also described the applicant’s request to waive an undergrounding requirement for roughly 232 linear feet of conduit, citing an estimated cost to the applicant of about $186,000–$232,000 and a project‑scale hardship.

Councilmember Eric Weber moved the resolution to approve the tentative parcel map; Councilmember Nakano seconded. The motion carried 4–1, with Councilmember Ryan Vienna recorded as the lone opposing vote. Council members who spoke said they regretted the impacts on neighbors but cited legal limits and potential litigation risk if the city denied a project that meets objective standards.

The council included conditions that require the applicant to repave the portion of Kimberley Avenue adjacent to the property and to meet the city’s tree‑replacement requirements. Staff told the council they will review landscape plans during building plan check and that the final construction permits will carry standard plan‑check conditions.

Next steps: The approved tentative map allows the applicant to proceed to design review and building permit plan check. Residents asked staff to explore private‑street maintenance options, including assessment/maintenance districts, and to return with options for resident coordination and potential funding mechanisms.

Clarifying details: Staff presented the applicant’s cost estimate for undergrounding (about $186,000–$232,000) as part of the waiver request; the city indicated it would require 2-for-1 replacement for removed mature trees (replacement species proposed: California sycamore, 24‑inch box). The record shows one public comment submitted to the Planning Commission that staff provided to council tonight.