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Third Party Evaluation for P&B Horizontal Diaphragm with SPF Dimension Lumber

Hidehiko Fumoto

By Hidehiko Fumoto

Deputy Director and Manager Technical Services, Canada Wood Japan

February 4, 2014

fumotosanDated December 24th, 2013, a certificate was issued to indicate that SPF dimension lumber performs sufficiently for the use in the horizontal diaphragms for post & beam structure.  This is the third party voluntary evaluation certificate to authorize the use of the SPF dimension lumber being equally safe to the traditional rafters and floor joists with a minimum thickness of 45mm.  While the Building Standards Law does not technically require structural calculations to be performed for 2 storey or less residential dwellings, for SPF in post and beam homes, these calculations are now required in three storey structures. The housing industry is also required to perform structural calculations on 2 storey structures to satisfying MLIT’s Housing Performance Labeling System and Long Life Quality Housing Standards.  Currently, an estimated 25 percent of single family post and beam structures are designed to meet Long Life Quality Housing requirements. Even in cases where structural calculations are not required in two storey houses, it is now standard industry practice by pre-cut manufacturers and builders to provide such calculations as a service included with the structural materials package.  FY2013-2014 COFI market access project has completed test work of SPF in P&B applications and formed a special technical review committee of structural experts to review and endorse the test results.  This certificate from these technical experts will provide a powerful tool in garnering market acceptance of SPF CLS sizes in P&B housing applications.  As a next step, COFI will proceed to one of FY2014-15 market access projects to develop an SPF annex for the HOWTEC Greybook Structural Manual widely regarded as the bible for architects designing post and beam housing in Japan