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Council reviews proposed 2026 Engineering Development Manual and code changes, asks about ADU stormwater charges
Summary
City engineers proposed code amendments to align municipal code with a 2026 Engineering Development Manual, including new permit types, a 3‑year stormwater look‑back, clarified undergrounding thresholds and revised driveway standards; council asked for clarification on ADU ERU assignment and driveway rules.
City engineering staff presented proposed updates to the Mountlake Terrace Municipal Code and the city’s Engineering Development Manual (EDM) at the Feb. 2 council work session, describing technical changes staff say will modernize development standards and align code with the EDM.
Lucas Crott, the city’s civil engineer, told the council the package aims to consolidate references to the EDM, remove conflicting or duplicate development standards from the municipal code, and add permit types to reflect current practice. Significant EDM changes described included clarified overhead utility undergrounding requirements (generally within 50 feet of the nearest pole), revised pavement‑cut rules that would allow cuts in recently constructed streets if a 50‑foot grind and overlay is performed in both directions, and updates to driveway/approach dimensions and right‑of‑way widths.
On stormwater billing, staff proposed defining all single‑family homes as 1 ERU and charging accessory dwelling units (ADUs) 0.5 ERU. Crott explained the approach to the council: "Our current rules call out the square footage for a commercial is 2,282 square feet of impervious area. And so all single family in the city are defined to be 1 ERU. And based on the ADUs being thousand square feet or less, 1 half seemed to be about that right size." Councilmember Murray asked whether 0.5 ERU would still be reasonable if multiple ADUs were allowed on a single lot; staff said the fixed 0.5 ERU was chosen for clarity and administrative simplicity and that they would watch how it plays out as development patterns change.
Council members also pressed on driveway standards. Staff explained that the proposed rule allows minimum driveway widths of 12 feet where the driveway length is short (less than about 100 feet) so that single‑lane access is possible, and that widths increase to 16 feet for longer driveways to permit two‑way passing. Crott said private property driveways can be wider than the public minimums and that turning‑radius standards remain in the EDM to ensure safe vehicle movement.
Planning Commission considered the amendments in a Feb. 9 meeting and recommended adoption; staff said the next procedural step is a public hearing and council action scheduled for March 5. No votes were taken during the Feb. 2 work session; council asked for continued review and clarification on implementation and budget impacts.
The council also used the discussion to thank CED staff for coordinating code clean‑up work and to recognize the need to monitor administrative impacts, such as how ERU assignments influence future development and billing.
