Experience from Seismic Zones and Past Earthquakes

In the seismically active zones of British Columbia, Canada, wood construction was chosen, in part, for its advantages. In 2016, WoodWORKS! BC completed a study that shows that wood is an effective building material in the seismic upgrades of schools in coastal B.C. The study provides detailed breakdown of the design approach and building systems used in various schools and included CLT, NLT and other mass timber products.⁴

In 2002, the California Department of Government Services completed a legislated inventory and earthquake worthiness assessment of schools. School buildings that were constructed of steel, concrete, reinforced masonry or mixed systems designed between 1933 and July 1, 1979 were required to be evaluated. Older wood-frame schools were exempted on the basis that “wood-frame buildings are known to perform well in earthquakes.”⁵

Following is a brief summary of the way wood-frame buildings have performed in North American earthquakes:⁶
San Leandro earthquake, 1971: The earthquake affected commercial buildings and many single-family homes as well as hospitals. Many masonry buildings with design faults collapsed or were severely damaged and had to be demolished. This shows that buildings that appear to be “solid” are subject to damage if their design and construction does not meet modern code requirements. Wood-frame houses performed well, especially from the standpoint of life safety.

Loma Prieta earthquake, 1989: The earthquake caused the collapse of a number of engineered structures including the double deck freeway in Oakland that resulted in the death of 49 motorists. Houses at the epicenter—most of which were wood-frame construction—were subjected to high peak ground accelerations and performed well unless they were located where ground fissures developed or had large openings in lower story walls.

Northridge Earthquake, 1994: Though moderate in size (magnitude 6.7 on the Richter scale), the peak ground accelerations were among the highest ever recorded and significantly higher than those specified in building codes at the time. There were numerous building collapses, including many large structures. At a hearing before the U.S. House of Representatives by the Committee on Space, Science and Technology, one of the reasons given for the limited deaths and injuries was: “The earthquake occurred at 4:31 a.m., when the majority of people were sleeping in their wood-frame, single-family dwellings, generally considered to be the safest type of building in an earthquake.