Mirrormont Landscaping Rules: Tree Trimming Rules (2026)

KCC Title 21A.24 (Critical Areas) and Title 16.82 (Clearing and Grading) regulate trimming and removal of significant trees and vegetation in sensitive areas. Routine maintenance pruning of landscape trees on a residential parcel generally does not require a permit. However, trimming of trees over 6 inches diameter at breast height (DBH) in critical area buffers such as wetland, stream, fish and wildlife habitat conservation areas, or shoreline zones may require review, particularly if it alters the character of the canopy. Crown reduction or topping of trees in stream buffers can remove shade critical to salmon habitat and is generally prohibited without a permit under the Critical Areas Ordinance. Trimming trees within a county right-of-way requires a right-of-way permit from King County Road Services (206-477-8100), which also manages hazard-tree removal along county roads. For neighbor trees that overhang a property line, Washington common law allows a neighbor to trim branches back to the property line but not to enter the neighbor parcel or destroy the tree. Forest Practices on parcels larger than 20 acres or in commercial forest are regulated by DNR under RCW 76.09.