New 90-Minute Fire Approvals Advance Midrise 2×4 Construction in Japan
On June 30 MLIT jointly awarded Canada Wood Japan and the Japan 2×4 Home Builders Association Ministerial Approvals for 90 minute fire-resistant exterior and interior wall assemblies. These approvals significantly enhance the competitiveness of 2×4 construction in Japanese midrise structures. Some background context might be helpful here.
In 2023 MLIT implemented changes to BSL fire code requirements to facilitate the expansion of structural wood use in large and midrise structures. Previously, buildings ranging from 5 to 9 storeys required 120-minute fire resistant ratings. However, achieving these 120-minute ratings in wooden construction required the use of a staggering amount of encapsulation: 3-layers (21mm + 21mm +21mm) of gypsum board on both sides of the wall assemblies, resulting in significant added weight, difficulty in assembly and impractical construction costs. However, the 2023 code revisions allow for 90-minute fireproof performance in structures between 5 to 9 storeys. To enhance the competitiveness of 2×4 construction in midrise applications and capitalize on these code revisions, Canada Wood Japan jointly initiated a 2-year technical project to secure recognition of a suite of 90 minute fire-resistant exterior and interior walls assemblies with the Japan 2×4 Home Builders Association.
Under the newly obtained 90-minute fire resistant certifications, we were able to reduce the number of required gypsum boards down to 2-layers (25mm + 25mm) per side. The 90-minute approvals are conservatively expected to reduce 5 to 9 storey midrise wall assembly labour and materials costs by 15%.
“The greatest achievement of this exterior wall ministerial certification is that 1.5-hour fire resistance is secured by the substrate assembly alone, without relying on the fire performance of the siding. While keeping the thickness of the fire-protective covering roughly equivalent to the notification specification, 15 mm furring strips reliably provide a ventilation cavity (durability). Because the specification does not restrict the product specification of the siding, it offers a high degree of versatility and can flexibly accommodate future changes to exterior finish materials.”
Between 2024 and 2026 a total of 4 MLIT Ministerial 90-Minute Fire Resistive Approvals (3 interior and 1 exterior wall assemblies) were jointly awarded to Canada Wood Japan and the Japan 2×4 Home Builders Association. Completion of this series of joint approvals represents an important milestone in removing technical barriers and advancing the 2×4 construction method into the pole position to lead growth in Japanese wooden midrise construction.