Understanding Seattle’s Tree Protection Ordinance
The purpose of Seattle's Tree Protection Ordinance is to answer the question, "how can Seattle build enough housing while also keeping enough trees?" The ordinance doesn't simply ban tree removal or allow unrestricted cutting. Instead, it tries to balance two important goals: protect Seattle's urban forest, and allow reasonable development of private property. For anyone building or adding to a home in Seattle, understanding the rules of this ordinance is a must.
Background
Seattle's tree protection programs were established to preserve and expand the city's urban canopy. The primary reasons for this initiative include fighting climate change, protecting public health by reducing urban heat and improving air quality, and promoting environmental equity across historically underserved neighborhoods. Seattle's Tree Protection Ordinance is a rulebook governing when trees can be removed, when they must be protected, and when new trees need to be planted.
Overview of tree classifications and allowable removal
Tier 1: a heritage tree-highly exceptional, celebrated trees (more info here). These trees may only be removed if hazardous or in an emergency situation.
Tier 2: Generally trees at 24" diameter or greater at standard height (DSH). May be removed as part of a building permit application only if necessary for construction of new structures. replacement trees required for those removed.
Tier 3: Trees with DSH between 12 and 24 inches. May be removed as part of development permit, replacement trees required for those removed.
Tier 4: Trees with DSH between 6 and 12 inches. May be removed as part of development permit, replacement trees not required.
In order to retain trees in Neighborhood Residential zones that would otherwise need to be removed to allow feasible development, extensions into the front and rear setbacks are permitted up to certain limits.
Protection of trees to remain
The ordinance also protects trees during construction. If you're building or remodeling, you may have to design around important trees and fence them off so roots and trunks aren't damaged by construction equipment.
Required replacement trees
When Tier 1, 2, or 3 trees are removed, new trees usually must be planted or other mitigation requirements met in order to prevent the gradual loss of Seattle's tree canopy. Note that these replacement trees can also fulfill Green Factor and tree points requirements.
Tree protection and planning
Seattle's Tree Protection Ordinance is complex-19 printed pages in fact. But the underlying purpose is easily understandable-maintaining Seattle's tree canopy without reducing development of much-needed housing in our neighborhoods.
Navigating this complex rulebook, identifying trees that are to be protected or removed and replaced, and a building layout that works with instead of against the tree canopy should occur as early in the planning process as possible.
Resources
Seattle Land Use Code, Chapter 25.11 Tree Protection
Types of tree protection areas and their impact on allowable building site coverage
Heritage Tree Program (determines Tier 1 trees)
Director's Rule on payment in lieu of providing replacement trees
Director's Rule on requirements for replacement trees
Director's Rule on designation of Tier 2 trees under 24" DSH
