Two-by-Four Housing Day (Two-by-Four Juutaku no Hi)

What Is 2x4 House Day?

October 24 is "2x4 (Two-by-Four) House Day" in Japan. It was established by the Japan 2x4 Home Builders Association to promote two-by-four homes and improve the technology. The date combines October, a month associated with housing in Japan, with "24," since the method uses many standard lumber pieces measuring 2 by 4 inches in cross-section. The association also treats the 24th of every month as "2x4 Day."

A History of the 2x4 Method

The two-by-four method is formally called "platform frame construction" (wood-frame wall construction) in Japan.

• Born in North America: In 19th-century North America, a method of nailing together standardized, slender lumber emerged and was refined into its current form. Because it did not rely heavily on master carpenters and allowed stable-quality homes to be built in a relatively short time, it became the mainstream method for wooden houses in North America.
• Introduction to Japan: In Japan, the method is said to have been opened up for general use in 1974 (Showa 49), after which house builders and contractors increasingly adopted it.

2x4 Homes and Earthquakes

A 2x4 house is supported by six surfaces - floor, walls and ceiling - and is said to spread earthquake forces across the whole building.

• The Great Hanshin-Awaji Earthquake: After the 1995 earthquake, a survey by the Japan 2x4 Home Builders Association reported that about 97% of 2x4 homes in the affected area had "no particular damage" or were "livable without immediate repairs."
• The Great East Japan Earthquake: After the 2011 earthquake, the association's survey likewise found that most 2x4 homes, excluding tsunami damage, were livable without repairs.

2x4 House Trivia

• Supported by surfaces: Japan's traditional post-and-beam method is supported by "lines" of columns and beams, while 2x4 homes are supported by "surfaces" of walls and floors.
• Fire-stop structure: Framing members inside walls and at floor-wall joints block the paths fire would travel, so fire is said to spread less easily.
• Airtightness and insulation: Built from panels, the structure has few gaps and makes it easy to install insulation.
• Two-by-six: There is also a "2x6" method using 2-by-6-inch lumber, which allows thicker walls and more insulation.
• Renovation limits: Since the walls carry the load, removing walls or adding large windows during renovation is restricted.

Ideas for 2x4 House Day

• Check your house's construction method in its drawings or documents.
• Review your earthquake preparations, such as securing furniture and checking emergency supplies.
• Visit a housing exhibition to compare homes built with different methods.
• Check when your home is due for inspection and maintenance.

Something to Remember on 2x4 House Day

October 24 is a day to look back on how a North American building method took root in Japan, and to take a look at your own home. Our homes support our everyday lives. Take a moment today to check how your house is built and how prepared you are for earthquakes.