Clearances and setbacks
The following setbacks and clearances shall be used for On-Site Stormwater Management BMPs in the public right-of-way. For more information on clearances, see the Design Standards Clearances section.
|Category/Utility||Description of Setback/Clearance Requirement from On-Site Stormwater Management BMPs|
No power pole within bioretention cell or rain garden.
5-foot (radius) level area around power poles.
|Guy wires||Typically 5-foot minimum clearance from top of bioretention cell or rain garden. However, more may be required by Seattle City Light if it is for a pole with transmission, primary or heavier load. Down guy and/or anchor pole shall not be located in bioretention cell.|
|Franchise/Electrical vaults||Not allowed within bioretention cell or rain garden section.|
|Underground duct bank for primary & secondary service||Not allowed within bioretention cell or rain garden section, unless approved by Seattle City Light / utility purveyor.|
|Electrical vaults and Bioretention cell vertical wall||See Seattle City Light Construction Standards for clearance requirements for different vault types.|
|Franchise vaults and Bioretention cell vertical wall||See Franchise Utility purveyors’ standards for clearance requirements. General guidance: provide 5-foot clearance for future maintenance/construction clearance for wall/vault.|
|Underground electrical service conduit to a single-family residence (not encased in concrete)||May be located within the bioretention cell, rain garden or permeable pavement footprint but prefer outside due to future maintenance. When located within the bioretention cell footprint the electrical service conduit to route under the bioretention soil mix and supporting infrastructure (i.e. underdrain). Maintain SCL standard clearance from other underground piping.|
|Gas mains and services – Plan||May be located within the bioretention cell, rain garden or permeable pavement footprint but prefer outside for ease of maintenance access. Maintain standard clearance from other utilities.|
|Gas mains and services and vertical wall for bioretention cells||General guidance is to provide 5-foot clearance for construction of wall and/or future repairs of service/main, unless noted otherwise by utility purveyor (PSE).|
|Gas mains and services – Section||Maintain minimum cover over gas service/main per PSE. When located within the bioretention cell, rain garden or permeable pavement footprint the service shall be relocated to route under the bioretention section and supporting infrastructure (i.e. underdrain). Maintain standard clearance from other utilities.|
|Underdrain pipe cleanouts and bends||Cleanout required at/near bends used for routing underdrain around existing power poles and hydrants.|
|Underdrain pipe for bioretention cells & new street trees||
If section of underdrain pipe is slotted then provide minimum 5-foot horizontal separation between new street tree and slotted underdrain pipe.
If section of underdrain pipe is solid wall then provide minimum 3-foot horizontal separation between new street tree and underdrain pipe.
|Water Service & Meters|
|Water service and meter||
Service may be located within the bioretention cell or rain garden footprint but prefer outside due to future maintenance.
Minimize locating bioretention cell or rain garden over water service piping that would require full replacement of the water service pipe (e.g. existing galvanized iron or plastic pipe) from the meter to the water main.
Meter shall be relocated to the back of walk in a landscape area within the right-of-way (preferred) or into the sidewalk.
|Water service and meter crossing through bioretention cell and rain garden||
Provide minimum depth of cover per SPU water.
If there is an underdrain, service may be above underdrain pipe as long as minimum depth of cover is provided.
Maintain standard clearance from other utilities per Standard Plans and Specifications.
Meter/vault shall be located outside bioretention cell and rain garden.
|Water mains (Cast iron with lead joints and ductile iron with slip joints)||
Provide cover for water main pipe per Standard Plan 030.
Horizontal setback distance from the water main (measured from the edge of the pipe to the edge of any bioretention cell*) must be minimum of 3.5′ for water mains up to and including 12″∅ water mains. Water mains larger than 12″∅ must be evaluated and approved on a case by case basis by Seattle Public Utilities. If soil within setback is disturbed, a support plan and soil re-compaction to 95% min compaction will be required. Zone of influence of the water main is a plane form the spring line of the pipe extending down and away from the main at a 1 to 1 slope. Exceptions to the minimum 3.5′ horizontal setback must be approved by Seattle Public Utilities plan review section and water quality division.
*Bioretention cells shall be located in Landscape/Furniture Zone – the area between the roadway curb face and the front edge of the pedestrian clear zone. See 3.2 Sidewalks Design Criteria for additional guidance.
Provide settlement monitoring if construction impact is closer than 10′ to any cast iron water main and more than 5′ to any ductile iron water main. Construction impact includes breaking up pavement with heavy equipment.
|Water main/services and vertical walls for bioretention cells||Review separation for horizontal clearance requirements with SPU water department. General guidance to provide 5-foot clearance for maintenance/construction of vertical wall.|
Provide minimum 3 feet of cover over pipe to hydrant.
Provide 4-foot level area (4-foot radius from center of hydrant).
No plantings except ground cover/sod within 4 feet of hydrant.
Not allowed within footprint of bioretention cell or rain garden.
Minimize locating bioretention cells and rain gardens at locations that would require relocating a fire hydrant since this will increase project costs. Relocating hydrants typically requires full replacement of hydrant lateral piping to the water main.
|Signage||Locate signage for sight lines and in accordance with SDOT requirements.|
|Side Sewers/Service Drains|
|Side sewers/Service drains||
May be located within the bioretention cell, rain garden or permeable pavement footprint but shall maintain clearances from underdrain pipes if included in the design. Maintain standard cover and clearances.
Avoid locating infiltrating bioretention cells, rain gardens and permeable pavements over existing side sewers unless the side sewer is replaced since the stormwater could flow into the pipe at a crack or joint in the side sewer.
For non-infiltrating bioretention cells or rain gardens over existing side sewers, the bioretention cell or rain garden section (including underdrain if used) shall be above side sewer.
|Lined Bioretention and Street Trees||
Lined Bioretention Cells must be designed for compatibility with street tree planting standards. New bioretention cells shall not be located within 5’ of a standard proposed street tree location or within the dripline of an existing tree to be retained.
For additional guidance to locate trees within bioretention facilities, see SPU GREEN STORMWATER INFRASTRUCTURE details BTP-1 through BTP-7.
See SPU’s GREEN STORMWATER INFRASTRUCTURE Tree Lists for trees allowed by both SDOT and SPU for use in bioretention facilities.
|Existing Street Trees and Bioretention||No new bioretention shall be sited within the dripline of any existing tree to be retained, including both street trees and trees on adjacent parcels.|