Canada Wood Today | The Canada Wood Group

COFI Technical Development Now Yielding Results: Daito Trust Adopts 2×6 SPF in P&B Apartments

Hidehiko Fumoto

By Hidehiko Fumoto

Deputy Director and Manager Technical Services, Canada Wood Japan

February 10, 2015

rafterAs a result of COFI’s technical research and activities to promote SPF dimension lumber use in post and beam construction, Daito (Trust) Kentaku1), one of Japan’s top housing companies2), has recently decided to adopt SPF dimension lumber in their P&B multi-family homes. As standard structural members, they have specified 2×6 SPF dimension lumber for roof rafters in their row house type Post & Beam apartment buildings. According to Mr. Miwa, who belongs to the company’s design department, the company has sought a way to specify dimension lumber in their apartments, but they required the technical basis to perform the required structural calculations. Normal practice for wooden structural engineers is to reference the HOWTEC Grey Book, a bible for P&B structural design. However, the Grey Book does not reference dimension lumber for horizontal diaphragms such as floor and roof assemblies.

Subsequent to our extensive horizontal diaphragm testing of SPF dimension lumber in post and beam assemblies, COFI developed a voluntary evaluation certificate from a Japanese government authorized testing body which serves as an alternative guidance basis to the Grey Book, thus permitting designers to conduct structural calculations of CLS lumber in P&B applications. Through technical consultations and support from COFI Tokyo, Daito Kentaku has become the first major company to adopt the use of SPF dimension lumber in P&B buildings where structural calculations are employed. Daito Kentaku is planning to build their first P&B apartment with 2×6 roof rafters in Numazu City, Shizuoka Prefecture in February, 2015


  • In FY2013, Daito Kentaku recorded housing starts of 61,520, the largest among Japanese housing companies.