Planning commission debates ADU lot‑coverage, setbacks and measurement rules; tables nonconforming‑structure rebuild language

Leavenworth Planning Commission members discussed draft changes to the city’s accessory dwelling unit regulations on March 5, focusing on how to increase allowable lot coverage, alter rear yard setbacks for ADUs, measure gross floor area and apply parking requirements.

Staff presented two approaches to lot coverage: a percentage‑based bonus tied to lot area and a fixed step increase by unit. Maggie (staff member) explained that the commission had previously asked staff to compare the effects of allowing bonuses for lots starting at about 3,000 square feet versus 6,000 square feet and to decide whether increases should be per unit or fixed. "If you have 3,300 square foot lot or a 6,000 square foot lot, you get the bonus if you're adding density because you're adding 1," Maggie said while illustrating a 6,228‑square‑foot example that showed only about 300 square feet of additional buildable area if coverage rose from 38.5% to 40%.

Why it matters: Commissioners framed the changes as an infill incentive intended to make small‑unit rental housing and garage‑ADU combinations more feasible inside the current city fabric, while trying to limit negative effects on neighboring properties.

What staff and commissioners discussed - Lot coverage: Commissioners generally favored a modest, predictable increase tied to additional units rather than a variable percentage calculation. Multiple speakers suggested a structure like 35% for a single‑family house, 40% for a first ADU (or two‑unit situation) and up to 50% for three units (a hard cap was discussed). Staff noted a 5% per‑unit approach had been considered; commissioners discussed fixed steps instead. Maggie said the intent was to avoid creating a perverse incentive to build unusually large ADUs and to make outcomes easier to calculate. - Setbacks and height: The commission discussed lowering the rear yard setback from 15 feet to 8 feet for accessory structures used as ADUs when the ADU is limited in height. Commissioners repeatedly returned to a "give and take" idea: if the setback is reduced, the accessory unit should also be capped in height so it does not create a dominating two‑story massing next to neighboring yards. One compromise the group endorsed in discussion was an encroachment allowance limited to single‑story or a specific height (the draft language discussed a 20‑foot height limit for the encroaching portion). - Gross floor area and measurement: Staff recommended measuring ADU interior square footage using interior (inside wall) dimensions consistent with the state ADU statute and clarifying which spaces count as habitable. The commission supported excluding interior stairwells, garages and uninhabitable storage from ADU gross floor area calculations so the rules would not penalize small vertical circulation areas in small units. - Parking: The draft retained the baseline that each ADU requires an off‑street parking space, but staff proposed language to avoid cumulative new parking for multiple small units on a lot. The working idea discussed was that a single family with two ADUs would not trigger more than one additional off‑street parking space beyond what the primary dwelling already requires, to avoid an untenable parking burden on small lots. - Conversion of existing accessory structures: Commissioners discussed state rules allowing conversion of existing accessory structures (for example, detached garages) into ADUs even if the existing structure violates current setbacks. The group agreed conversion should be allowed, but they debated how to treat full demolition and reconstruction. That issue raised intersections with the city’s nonconforming‑structure rules (which call out a 75% reconstruction threshold) and the commission decided to postpone detailed new language on the nonconforming/rebuild question.

Formal actions and next steps - The commission voted to table detailed nonconforming‑structure and rebuild language for a future meeting so staff could reconcile the state ADU statute with the city’s nonconforming‑structure rules and produce clearer draft language for review. - Staff will redraft the ADU provisions to reflect the commission’s direction (fixed increases tied to unit count, 8‑foot encroachment option tied to a height limit, interior measurement of ADU gross floor area excluding stairs/garages and streamlined parking language) and run example lot scenarios before returning the draft for additional review.

Quotes "If you have 3,300 square foot lot or a 6,000 square foot lot, you get the bonus if you're adding density because you're adding 1," Maggie (staff member) said while showing a 6,228‑square‑foot example. "I think we have to do a trade off of some sort or another. So if you do want to get closer to the rear lot line and you're constrained by space, you have a kind of a height gap scenario," Allison Miller (Planning Commission member) said in describing the neighborhood impacts of a reduced setback.

Ending Commissioners asked staff to rewrite the draft with explicit, testable examples and a clarified definition of gross floor area (interior measurement for ADUs; exterior footprint for lot coverage). The commission tabled further work on nonconforming‑structure rebuild rules and will take up the redraft at a later meeting. Votes at this meeting on motions related to ADU language were procedural (see "Votes at a glance").