Building Code Council members debate IRC 'multiplex' appendix: stories, separations, sprinklers and shared spaces

Members of the state Building Code Council spent most of their Aug. 26 meeting detailing a proposed appendix to the International Residential Code (IRC) that would permit ‘‘multiplex’’ buildings — residential buildings of up to six dwelling units and up to three stories — and debating how those buildings should be defined and protected.

The council agreed on several baseline limits but left several major policy questions open, including whether to allow shared common areas or interior stairs that serve more than one unit, whether some projects could avoid automatic sprinklers if walls between units are built to higher fire-resistance ratings, and whether multiple multiplex buildings may be attached together. The group scheduled further work and assigned members to draft language on means of egress and separations for the next meetings on Sept. 9 and Sept. 23.

The matter matters because the appendix would let jurisdictions adopt a prescriptive alternative for small multifamily housing drawn into the IRC instead of the International Building Code (IBC). Proponents say that makes construction more affordable and easier to build on small infill lots; several council members and local officials warned that relaxing building-code requirements can raise life-safety risks and complicate water-supply and fire-access requirements.

Dustin (staff member) opened the discussion by reminding the group that the council had split its meetings to treat ‘‘single-exit’’ and ‘‘multiplex’’ topics separately. He walked members through a baseline draft and a separate proposal submitted by Marcus Johnson, who had asked the council to consider rules for attaching multiple multiplex buildings and for design flexibility.

The council settled a few basic limits: members expressed consensus that multiplex buildings in the appendix should be limited to three stories and 60 feet in height, matching sprinkler-system limits that apply under the IRC. “We’re all in alignment with 60 feet,” Dustin said during the discussion.

On definitions and attachments: the group spent substantial time on what ‘‘attached’’ should mean. Developers described projects in which modular units or buildings were connected by decks or exterior stairs; some jurisdictions had counted those as a single larger building. Marcus Johnson said he had prepared draft language to allow certain attachments and to cap the total number of attached units, noting design flexibility concerns: “I tried to put some language together,” he said.

Opposition from some building- and fire-code officials centered on scope creep. Several officials urged caution about allowing multiple multiplex buildings to be attached, saying the resulting structure could, functionally, become a low-rise apartment building that should be regulated under the IBC. One official summarized the safety and regulatory concern: if developers attach multiple limited-scale buildings without strong separations, the project can be built to IRC rules but present the same risks as an IBC-regulated multifamily building. That view led multiple speakers to argue the appendix should limit a single building to six units and preserve IBC requirements for larger consolidated projects.

Fire protection and sprinklers drew some of the most detailed debate. Several speakers — including fire officials and building-industry representatives — summarized differences among nationally used sprinkler standards and how they apply.

Mike Messer (committee member) explained that stacked-unit arrangements (units over units) typically compel a different sprinkler approach than side‑by‑side townhouses. “13R systems are required to be maintained,” Messer said, and they carry different installation, water-supply and inspection implications than 13D systems, which are written for single‑family and duplex occupancies.

Fire officials said sprinklers reduce fire flow requirements at the hydrant and limit displacement of occupants and property loss; they also warned that some sprinkler options create ongoing maintenance and monitoring responsibilities for owners or homeowners associations. Several speakers called attention to lithium‑ion battery fires and cooking fires as common residential ignition sources and said sprinklers materially reduce the scale of those losses.

Some developers asked whether an alternative could allow higher fire-resistance ratings on unit separations in lieu of sprinklers. Marcus Johnson proposed an exception that would permit a project to omit sprinklers if the separating wall and floor assemblies between dwelling units were rated at two hours instead of one. Officials replied that the national sprinkler standards and the codes that reference them generally limit 13D application to single‑family or duplex occupancies, while stacked multiplen-units typically fall under 13R or full NFPA 13 design. That technical distinction means the council cannot approve a residential sprinkler design that conflicts with the national sprinkler standards without developing a separate state-specific standard.

Means of egress and common areas were another major locus of debate. The draft appendix treats multiplex buildings as residential apartment use limited to dwelling units, but council members discussed whether to allow shared laundries, bike or storage rooms, interior stairs or corridors that serve more than one dwelling unit, and whether such spaces would trigger additional separations, opening-protection, or accessibility requirements. Building and fire officials worried that ‘‘common use’’ rooms increase hazard exposure when they are not constantly supervised and may bring additional code obligations, including accessibility and higher sprinkler or separation requirements.

On architectural definitions, several practitioners urged the council to avoid language that would force ordinary rear decks or shared exterior walkways to be counted as ‘‘attachments’’ that change a project’s regulatory status. Derek Kimball (Wolf Industries Inc., modular home manufacturer) described a local project where a 12‑foot‑wide deck connecting two fourplex buildings was treated by a plan reviewer as creating a single eight‑unit building. That uncertainty, he and others said, undercuts the appendix’s goal of predictable, affordable design.

Next steps and assignments: the council did not adopt final regulatory text. Instead members agreed to continue work: Dustin said he would reconcile the baseline draft with Marcus Johnson’s proposal and circulate revisions. Angela, Rich Williams and John Hsu (committee members) volunteered to draft tighter language on interior stairs, corridors and means of egress for the next meeting. The council also asked staff to revisit the sprinkler question with additional technical input so members can weigh performance, water-supply and maintenance tradeoffs.

Two formal housekeeping votes took place at the meeting’s start: the body approved the agenda and the minutes from Aug. 12 by voice vote.

The council will revisit the multiplex appendix at its next dedicated sessions on Sept. 9 and Sept. 23; members said they expect to return with specific redlines on means-of-egress rules and clearer options on sprinklers and attachments.

Ending: The discussion left several key policy choices unresolved. Council members asked staff and subject-matter participants to return with proposed text and technical analyses — especially on egress configurations, separation continuity, and sprinkler options — so the group can move from conceptual debate to concrete code language.