Joist Blocking, What For?
Joist blocking and seismic retrofitting don’t have anything to do with each other. This video looks at joist blocking that is unique to the International Code Council’s seismic retrofit guideline ICC 1300 Vulnerability Based Seismic Assessment and Retrofit of One and Two-Story Dwellings. It is the only retrofit guideline that anticipates a type of damage that has not been seen in previous earthquakes. Here will we look at the logic that is the basis of its inclusion in this retrofit guideline and why it believes joist blocking and seismic retrofitting are related.
According to the International Residential Code, the building code that governs the construction of one and two-story dwellings, joist blocking is only necessary if your joists have a depth greater than 12”. Therefore, for most houses, you are not required to have blocking or bridging if you have traditional lumber joists that are 2” in thickness and up to 12” in width as long as both ends are fastened properly. In other words, put blocks at the end or have rim joists and you will be compliant with new construction.
Here you see a long span of floor joist that only have blocks on the ends. This is fully compliant with the International Residential Code.
The older one and two-story dwellings we work on almost always have blocks on the ends. Very rarely, in some early century houses, we don’t find either blocking or rim joists. Fortunately, ICC 1300, Vulnerability Based Seismic Assessment and Retrofit of One and Two-Story Dwellings has a construction detail that addresses this problem. Recommending blocks installed in this manner is unnecessary and expensive.
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