Successful 90-Minute Fireproofing Tests Pave Way for Cost-Effective 2×4 Midrise Construction in Japan
In a joint effort to advance fireproofing solutions for midrise 2×4 construction, Canada Wood Japan and the Japan 2×4 Home Builders Association conducted a series of fire resistance tests to develop 90-minute fireproof assembly approvals. This initiative follows a key revision to Japan’s Building Standard Law in 2023, which reduced the fire resistance requirement for midrise structures from 2 hours to 90 minutes for buildings up to nine storeys. This important testing work paves the way for more cost-effective and practical fireproofing solutions that strengthen the competitiveness of 2×4 construction in Japan’s midrise sector.
Currently, midrise 2×4 builders must comply with MLIT’s 2-hour fireproofing requirement, which necessitates three layers of gypsum board on both sides of walls, stairs, floors, and ceilings. This increases material costs, adds weight, and complicates construction. However, the recent regulatory change allows for 90-minute fireproof solutions, which present an opportunity to develop a more efficient and economical assembly using just two layers of gypsum board.
In November 2024, fire resistance tests were carried out at the General Building Research Corporation in Ikeda, Osaka. The test specimens included two platform wood-frame wall assemblies: one with insulation, representing a partition wall, and one without insulation, representing an interior wall. Both assemblies utilized 2×6 SPF (Spruce-Pine-Fir) studs and two layers of 25mm gypsum board, resulting in a total wall thickness of 288mm. The tests confirmed that both assemblies met the 90-minute fire resistance requirement, with no damage to the structural members.
Based on these successful results, Canada Wood Japan and the Japan 2×4 Home Builders Association have submitted applications for Ministerial Approval to MLIT, with approvals anticipated by June 2025. Once granted, these new fireproofing approvals will reduce material and labor costs, making midrise wood-frame construction more viable and competitive in Japan’s evolving building landscape.
