Chuck Dillon, building official for the City of Moundsburg, told residents at a city meeting that homeowners planning accessory dwelling units should use plans that comply with Washington State building and energy codes and follow local design criteria for seismic, wind and snow loads.

Dillon said the guidance matters because many applicants submit out-of-state plans that do not meet Washington State requirements and because following the code's prescribed path can reduce costs. “We got 3 of them on back table,” he said, referring to printed guidance documents that explain ADU standards, design criteria and the permit process.

Dillon listed several technical and life-safety items that often cause problems. He said energy-code compliance should be evaluated early and that the code's prescribed path can avoid unnecessary engineering costs. He warned that structural design must address local seismic, wind and snow loads, and that fire-separation rules differ for attached and detached ADUs.

On fire separation, Dillon said attached ADUs require a one-hour separation wall and that openings are restricted. “It's gotta be a 1 hour complete separation all the way through and no penetrations within 4 feet on both sides of the group,” Dillon said. He added that building an ADU too close to the primary residence can trigger additional firewall requirements of up to one or two hours depending on separation distances.

Dillon also described life-safety and access requirements. Addressing must clearly identify the main structure and the ADU, and pathways to the unit must be at least 3 feet wide and be hard-surfaced or compacted gravel; those features are inspected before the final certificate of occupancy is issued. He noted smoke and carbon-monoxide alarms must be hardwired together.

On electric-vehicle charging, Dillon said Washington State Building Code includes narrow conditions that trigger requirements. “If you have a garage, all 4 sides enclosed, that requires an EV charger,” he said, and contrasted that with carports, where he said an EV charger is not required if only two sides are enclosed.

Dillon warned that new state codes are due soon and that applicants often rush projects to qualify under older standards. He said the new building and energy codes were scheduled to take effect in November 2026 and advised homeowners to start planning early if they want to qualify under the current code.

There was no formal action or vote during the remarks; Dillon provided information and said he and staff would be available after the meeting to answer questions. He identified staff contacts and printed guidance materials on a back table for applicants seeking details on permit submittal and design criteria.

For homeowners considering an ADU, Dillon recommended early consultation with city staff, reviewing the three guidance documents available at city hall, and verifying that plans explicitly meet Washington State building and energy codes to avoid redesigns or additional costs.