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Mountlake Terrace staff pitch Engineering Development Manual updates, including ADU stormwater rule and narrower local street widths
Summary
City staff presented proposed municipal code updates and a revised Engineering Development Manual to consolidate standards, define ADUs as half an ERU for stormwater billing, tighten stormwater evaluation to a three‑year lookback, and reduce local street curb-to-curb widths.
Lucas Crott, civil engineer with the City of Mountlake Terrace, presented proposed updates to the municipal code and the Engineering Development Manual (EDM), saying the changes are intended to consolidate scattered engineering standards and remove conflicting code language.
Key proposals include codifying accessory dwelling units (ADUs) as half an equivalent residential unit (0.5 ERU) for stormwater billing and capital facility charges; carving out small exceptions to avoid requiring a permit for minor landscape disturbances; and changing how stormwater triggers are calculated by evaluating cumulative changes to a property over the previous three years rather than on a single-project basis. Crott said the current stormwater threshold that typically triggers measures is about 2,000 square feet of new impervious surface.
The presentation also proposed several design and technical edits: clarifying overhead-utility undergrounding requirements; allowing pavement cuts in recently constructed streets only when a grind-and-overlay is performed for 50 feet in each direction; adding driveway and driveway-approach standards with curb-to-property-line widths generally between 12 and 20 feet; and reducing local access street curb-to-curb width from 36 to 32 feet where appropriate while retaining parking on both sides.
Commissioners asked for specifics that will be relevant to the public hearing, including the per-ERU billing amount and examples showing how the ADU change would affect fees. Crott said the capital facility charge is currently "a little over $3,000" and agreed to provide clearer billing examples to staff for the public hearing materials. Commissioners also raised fire-access and grade concerns tied to narrower street and driveway standards; staff noted fire requirements would continue to overlay local standards.
Staff recommended the commission forward the code and EDM updates to the public hearing and, ultimately, to council for decision, citing the benefit of a single, consolidated set of engineering standards and reduced internal conflicts in the municipal code.
