Hey, I will admit to designing some places that utilized artificial turf. My point here is not to hash out the pros and cons of turf versus real lawns. Turf serves a real need - a solution to a problem caused by the fact that lawns simply don’t want to be here - in the Pacific Northwest.
It goes down similar to paving or flagstone, except for the use of a “clear” subgrade of crushed rock (not gravel), a designation that means that the small rocks are almost all equal size, allowing better drainage. This is critical for the installation (and a way to check that your contractor knows what he/she is doing). But - importantly, King county and the city of Seattle consider to turf to be impermeable, much like a Hardscape installation. A lot of folks aren’t aware that these areas are limited on your property, and ignoring this can cause drainage problems, further inhibit wildlife, and increase a homeowners personal and insurance liability.
What really riles me is the giant spreads of artificial turf that the turf companies are showing in all of their marketing. Are there not going to be any standards for impermeable surface anymore? Are these companies indemnifying themselves from future environmental concern when they arise? In my experience, most clients are not aware of the permeable surface limits that there are lots are subject to. My guess is that these types of companies are not bringing this to their attention at all.
Seems to me like bad things are going to happen. Clients need to be advised:
In King County, Washington, impermeable (impervious) surface limits are not standardized; they depend on your specific zoning district, the lot size, and whether your property contains Critical Areas. Limits typically range from 10% to 80%, though rural residential properties have much tighter restrictions.
Zoning and Lot Coverage Limits
Unincorporated King County regulates lot coverage and impervious surface under the King County Zoning Code (K.C.C. 21A).Rural and Resource Zones (e.g., RA, A, F): Impervious surface limits are heavily restricted to protect natural hydrology. Limits often cap around 10% to 20% of the total lot area, unless a larger maximum square footage is specifically approved.
Low-Density Residential (e.g., R-1, R-4, R-6): Lot coverage limits (which dictate the footprint of all structures) and surface water limits typically range from 30% to 60% depending on the exact zoning designation and parcel size.Urban/Commercial Zones: In dense urban areas and commercial/industrial zones, allowable impervious coverage can reach 60% to 80%.
Critical Areas RegulationsIf your property intersects with environmentally sensitive areas like steep slopes, wetlands, or stream buffers, your impervious limit will be significantly lower. King County’s Critical Areas Ordinance places strict caps on clearing and adding new impervious surfaces (such as driveways, patios, or roofs) within these designated buffers.
How to Find Your Exact LimitBecause these limits are parcel-specific, you will need to check King County's official development regulations:Identify your property’s zoning by searching your address on the King County iMap Interactive Property Tool.Look up the specific impervious surface and building coverage limits for your zone in K.C.C. 21A.12 (Dimensional Standards tables).
If you have environmental features on your land, you should apply for a Critical Areas Designation (CAD) to determine the buildable area on your specific lot.
