Study session on 50 Sycamore spotlights ADU for aging parent and demolition‑threshold, commissioners urge caution

The Planning Commission’s Feb. 10 study session on 50 Sycamore Avenue centered on a proposed remodel that includes a second‑story addition and an attached ADU intended for aging‑in‑place use. Staff and commissioners focused on whether the project could exceed the code’s 50% demolition threshold and on ensuring the ADU functions as a separate unit consistent with state and local ADU rules.

Associate planner Michelle Johnson said the proposal would convert about 800 square feet to an attached ADU, add roughly 1,119 square feet on the second story and currently calculates roof demolition at approximately 49.4 percent of the roof area. Johnson warned that if demolition goes above 50 percent the project could lose its nonconforming status and be required to meet current zoning fully; she said staff strongly recommended the applicant consider applying for a variance up front to avoid stop‑work and re‑review risks if construction finds additional concealed damage.

Applicants Kristen and Shan Morrow described the project as family‑driven: the ADU is intended to house an aging parent and the second story would provide bedrooms for their children. Architect Mark Fischbach said the team has placed story poles and conducted neighbor outreach and expressed confidence in the contractor’s ability to keep demolition within the proposed figure; he said the overall demolition (including roof and other components) is lower than the roof figure alone.

Commissioners requested more field verification and contingency planning: provide attic or crawlspace photos and engineering/contractor evidence to show there is no hidden rot or structural damage that would push demolition over 50 percent; identify which elements the 49.4 percent roof figure includes; and show how the project footprint could be reduced if demolition proved larger than expected. Several commissioners also stressed Mill Valley’s current reading of state ADU guidance: attached ADUs should function as separate dwelling units without internal connections that would effectively enlarge the principal dwelling. The chair and staff said fire‑rated assemblies can be used but that the city’s current practice treats attached ADUs as separate and requires demonstrable separation.

Other staff and commissioner guidance included encouraging permeable driveway materials to reduce runoff near the adjacent creek, working with the arborist and DPW on the sycamore street‑tree removal (staff reported the arborist found the tree hazardous and recommended removal), and ensuring any upper‑story windows minimize privacy impacts to neighbors. Because the item was a study session, commissioners offered guidance rather than taking action; they generally favored a path that minimizes the chance of mid‑project stop‑work orders by securing either evidence that the project will remain under 50% demolition or by applying for required variances up front.

Next steps: applicants were asked to submit additional documentation (attic/crawlspace inspections or contractor affidavits, a clearer demolition table, and refined setback/creek‑setback analysis) and to return for a formal design‑review hearing with any necessary variance applications.