Renton plans new surface‑water tiers by imperviousness, will apply 30% cap to state roads under state law

City staff told the committee they will restructure commercial surface‑water charges to bill based on parcel area and finer imperviousness categories so customers pay in proportion to runoff contributions.

"We're going to charge them based upon what percent of impervious, but under state law, we're only limited to charge them 30% of what we charge a comparable property," Ron Stroker said when describing how state Department of Transportation parcels (I‑405) and city streets will be billed using GIS‑determined impervious area and then reduced to the 30% statutory limit for state transportation corridors.

Staff proposed six commercial imperviousness tiers (very low to very high) to replace the current three tiers so smaller low‑impervious parcels do not subsidize large high‑impervious sites. They also said the city will treat gravel pits consistently based on impervious area, and that the city streets category falls in a higher imperviousness tier; applying the 30% cap produces an estimated city streets cost change of $83,191 to be phased over two years.

Stroker said the changes are intended to be revenue neutral overall and will be paired with whatever final percentage rate increases staff determines necessary under the 2027–28 budget. No formal vote was taken at the meeting.