Conservation Easements & the Transfer of Development Rights Program in King County

How the sending-site / receiving-site mechanism actually works

King County's Transfer of Development Rights Program, running continuously since 1998, is built around a simple but genuinely market-based idea: instead of simply zoning rural land at low density and leaving the landowner with no compensation for the development potential they're giving up, the county lets that landowner sell the development right itself as a separate, tradable asset. A 'sending site' -- a rural, forest, or agricultural parcel the county wants to see permanently conserved -- generates one or more TDRs based on its size and zoning. A developer building in King County's urban 'receiving' areas can then purchase those TDRs to build at higher density than the base zoning would otherwise allow, and the sending-site landowner is paid for rights they were never going to use anyway if the land stayed rural.

As of a May 2025 program update, this mechanism had protected more than 148,000 acres of rural and resource land and open space across King County since the program's founding -- a substantial, cumulative, and still-growing total that makes King County's TDR program one of the largest and longest-running of its kind nationally.

What enrolling a property as a sending site actually requires

Not every rural parcel automatically qualifies as a TDR sending site, and the process isn't purely transactional. Depending on the type of land, King County typically requires a Forest Stewardship Plan (for forested land) or a Farm Plan (for agricultural land) as part of enrollment, and certain categories of land -- parcels in designated rural forest focus areas, agricultural lands, or small nonconforming lots -- can qualify for 'bonus' TDRs, meaning the same acreage generates more tradable development-right value than a standard sending site would. Once a landowner separates and sells the development rights, the property is permanently conserved through a recorded conservation easement, which restricts future development on the eased portion of the property regardless of who owns it afterward.

The other direction: buying a TDR to unlock a receiving-site project

The TDR market runs both ways, and it's worth understanding even if you're not selling development rights off rural land. King County's rural zoning normally requires a full 5-acre minimum lot for a detached accessory dwelling unit under the RA-5 designation -- but the county allows a DADU on a smaller 2.5-acre portion of an RA-5 parcel if the owner purchases a Transferable Development Right to make up the density difference. For a buyer evaluating a smaller rural King County parcel specifically for its ADU or secondary-unit potential, purchasing a TDR through the county's program (or from an existing sending-site landowner) can be the practical mechanism that makes an otherwise infeasible project work.

1. If you own or are buying rural King County land you don't plan to develop, ask the TDR Program office directly whether it qualifies as a sending site, and what a Forest Stewardship Plan or Farm Plan enrollment would require.
2. If you're evaluating a smaller rural parcel specifically for ADU/DADU potential, ask King County Local Services whether purchasing a TDR is a viable path to unlock that use on the specific lot size you're considering.
3. Before buying land that's already enrolled as a TDR sending site, confirm the exact terms of the recorded conservation easement with the King County Recorder's Office -- the easement, not the general TDR program description, is what actually restricts the property going forward.
4. Check current TDR market pricing directly with the county's buy/sell resources before assuming a specific dollar value for a sending-site transaction -- pricing is market-driven and changes over time.