1. Building Demolition Permits May Trigger Full Drainage Review
Current Code: Drainage review is not required for demolition projects if the existing slab or foundation remains.
What’s Changing: Under the new code, demolition, regardless of whether the slab or foundation remains, will count toward the threshold for drainage review and approval.
Why It Matters: This update broadens the range of projects subject to drainage review and evaluation for detention, water quality, and on-site stormwater management.
From a project management standpoint, however, the added review may extend schedules for design, permitting, and construction and increase both scope and cost. Demolition permits that typically take fewer than four months to obtain could now face delays, as drainage analyses are completed and mitigation measures implemented, requiring additional coordination among design teams.
2. Utility Projects Will Require Drainage Review
Current Code: Utility work associated with parcel-based or roadway projects is currently exempt from drainage review and requirements.
What’s Changing: These projects may now trigger detention or water quality requirements in the right-of-way.
Why It Matters: Pavement restoration for utility work will now count toward drainage thresholds meaning we will see these projects requiring water quality treatment or detention systems more often. This will add design, reporting, and permitting steps, potentially increasing costs and extending project schedules.
As most of these utility projects are taking place in the right-of-way, permitting through Seattle Department of Transportation (SDOT) will be affected. So far, drainage code updates are in Seattle Department of Construction and Inspections’ (SDCI) court. We anticipate more information on how this affects SDOT permitting as the code updates progress.
3. Changes to Infiltration Requirements
Current Code: Infiltration is encouraged, but investigations are not often required since certain areas have been exempt based on known soil conditions.
What’s Changing: The new code will likely require more infiltration investigations early in the design process to demonstrate compliance with updated standards.
Why It Matters:
Infiltration is one of the preferred methods of stormwater management because it most closely mimics the natural water cycle by allowing runoff to absorb into the soil rather than enter the combined sewer system. It’s often a cost-effective approach that reduces overflow risk and improves water quality.
The City’s goal is to ensure infiltration has been fully evaluated before approving alternative stormwater solutions. However, implementing infiltration can be challenging and needs to happen early in the design process, as it requires specific soil conditions not found at many Seattle sites. Investigations need ample space and can take up to a year to complete.
