Planning Commission hears proposal to use gross area for R1 density; staff and commissioners flag environmental and infrastructure concerns

The Sammamish City Planning Commission received an introductory briefing on a proposal to change how residential density is calculated in the city’s R1 zone, including consideration of a pilot program that would use gross site area rather than net (constrained) area to determine the number of allowable dwelling units.

The change would raise the allowable number of dwelling units on sites that contain critical-area constraints by counting the full, gross parcel area when calculating density rather than subtracting wetlands, steep slopes, stream buffers and streets to arrive at a smaller net area. Robin Probsting, Associate Planner, told the commission: “This particular proposal asks to change the development regulations in the R1 zone only. It would change the density calculations so that gross area rather than net area is used to calculate how many units can be built.”

Commissioners were asked to provide feedback on selection and success criteria for a pilot program the City Council already put on the docket. The council’s docket motion (from a prior meeting) directed staff to evaluate a pilot program of up to five projects; staff emphasized that any pilot would need clear success criteria and limits so impacts remain modest and measurable.

Under current code, Probsting illustrated, a 30-acre parcel with 10 acres of land encumbered by critical areas yields 20 net acres; in the R1 zone (1 dwelling unit per acre) that produces 20 allowable units. A separate 50% open-space dedication requirement means the allowed units would be built on 15 buildable acres, resulting in 20 units on 15 acres. Under the proposed gross-area approach, the same 30-acre parcel would be allowed 30 units overall, and after the 50% open-space dedication those 30 units would sit on 15 buildable acres. Probsting summarized the example as: “you have 20 dwelling units on 15 acres” under the current system versus “30 dwelling units on 15 acres” under the proposal.

Staff and commissioners focused on points that would determine whether a pilot is appropriate for Sammamish: exclusions for sites where environmental damage would be irreversible; how the pilot should treat parcels lacking sewer (many R1 parcels remain on septic); whether projects in overlay critical-area zones should be eligible; limits on the total number of lots generated across pilot projects (the council has discussed numerical caps for related ECA pilots); and potential interactions with fee-in-lieu programs that could alter buffer impacts. Robin Probsting said staff will “unpack” applicable comprehensive-plan goals and policies, produce more maps and data, and propose both selection and success criteria for the commission’s review at the July 11 work session.

Commissioners requested additional analyses and materials before making a recommendation: real-world parcel examples of varying sizes and constraint levels (the 30-acre hypothetical was one example), maps zoomed to neighborhood/street level, an “impacts” chart that buckets significant versus minor effects and possible mitigations, confirmation from public works on how travel-model trip estimates treat constrained versus unconstrained acreage, and explicit treatment of sewer connection triggers and Department of Health septic limits.

Resident Gregory Kipp—identified in the packet as the proposal’s proponent—addressed the commission briefly during public comment and said he was in attendance to listen to the briefing and would provide further input in subsequent meetings. Robin confirmed she will deliver a staff report before the July 11 work session and that a public hearing is scheduled for July 25, after which the commission’s recommendation will go to council.

Next steps: staff will provide a written staff report and more detailed maps before the July 11 work session and will include proposed selection and success criteria. The commission will hold a public hearing on the item on July 25, then forward a recommendation to the City Council for a later decision.