Building Code Council weighs adding sound-transmission requirements for multiplex housing

At its July 14 special work session, the Washington State Building Code Council discussed a written proposal to add sound-transmission (sound attenuation) language to the new multiplex housing appendix, which would apply IRC-level requirements to six-unit buildings built under the residential code. Staff identified the proposal as coming from John Sue and confirmed the submission recommends "the IRC level."

Council members said sound transmission is a livability and health concern that the tag either did not fully address or could reasonably include in the appendix. One council member argued the addition "makes a lot of sense" because sixplexes put more households adjacent to each other than duplexes and townhouses. Public commenter Patrick Hanks, who identified himself as a representative of the Building Industry Association of Washington, said preliminary, non‑professional cost checks suggested an added material cost of about "$2 per square foot" for assemblies such as an extra gypsum layer or specialty rated gypsum and other detailing. Hanks cautioned those were informal estimates and said exact costs depend on assembly choices and how much wall area is affected.

Architectural and technical options discussed by council members and staff included adding resilient channels, extra gypsum layers on demising walls and floor toppings (gypcrete or lightweight concrete) to meet STC/IIC thresholds. Members noted that the IRC appendix is optional and that local jurisdictions sometimes adopt additional sound provisions by ordinance, so a narrowly drafted appendix reference could limit statewide mandates while improving minimum livability. A former fair-housing attorney in the public record said noise complaints were a frequent problem and supported including measures that reduce disputes and accessibility impacts.

The council did not take a final vote but agreed to gather more input from absent architecture-seat members (Vikram and Morgan) and to have a council member leading the multiplex/single-exit work draft a specific amendment. The council member volunteering to coordinate said they would "take on creating an amendment" and requested other members send comments. The amendment will be posted for review when ready.

Next procedural steps: staff will solicit the architecture-seat feedback and the designated council member will circulate draft amendment language ahead of a future meeting where the council may consider a formal motion. No statewide requirement was adopted at this session.