Commissioners debate requiring continuous R‑5 exterior insulation amid fire-code uncertainty

A significant thread of the work session centered on a proposed regional amendment that would require an R‑5 continuous exterior insulation layer in addition to cavity insulation. Staff and the building‑code cohort proposed the continuous R‑5 to reduce thermal bridging, but staff recommended caution because the state fire code has not yet clarified allowable exterior assemblies and could conflict with a prescriptive exterior insulation mandate.

“I disagree with it just because it might really tie your hands with the fire code,” a technical participant (speaker 3) said, noting that fire‑rating requirements could “severely limit design options for exterior walls.” Commissioners observed that most Ridgeway homes are 2x6 construction and that some compliance options — such as filling cavities with an R‑30 or using structural insulated panels (SIPs) — can achieve the same overall thermal performance, albeit at differing cost profiles. Participants also discussed lower‑cost continuous options (for example, stucco over R‑5) and the trade‑offs between energy performance, aesthetic variety and affordability.

Staff recommended allowing jurisdictions to pick and choose regional amendments and asked the commission whether to recommend not adopting mandatory exterior R‑5 until clearer fire‑code guidance is available. Commissioners asked staff to return with more detailed technical guidance, examples of acceptable assemblies and cost estimates before the March public hearing.