I-Joist Squash Blocks

In order properly distribute the weight from load-bearing walls, contractors must use I-joist squash blocks. Here is an overview of how squash blocks work, the load-transfer capacity of different materials, and how they should be cut and installed to ensure proper application in your project.


Builders use I-joist squash blocks to offset weight transfer from a load-bearing wall above. Typical application occurs when an I-joist cannot properly transfer the load from above due to limitations in interior and exterior reaction capacities. To properly transfer the weight and remove the risk of web-bearing failure, builders use I-joist squash blocks.


Typical squash block materials consist of lumber for maximum capacity, as well as APA Performance Rated Rim Board, and APA Rated Stud-I-Floor. 

Squash Block Load Transfer Capacities (pairs)

Up to 5,900 pound-feet of weight for a 2x6 and 3,800 pound-feet for a 2x4 can be transferred through the proper application of a lumber I-joist squash blocks, depending on the depth of the I-joist. 

APA Rim Board
Up to 4,000 pound-feet of weight for a 2x6 using 1-1/8" rim board and up to 3,000 pound-feet using 1" rim board;
Up to 2,600 pound-feet of weight for a 2x6 using 1-1/8" rim board and up to 1,900 pound-feet using 1" rim board.


  • Normally, squash blocks are used in pairs, installed at the end of an I-joist and intersecting the blocking panel. In order to reduce the risk of shrinkage in the block, the grain of lumber squash blocks run in line with or parallel to the grain in the vertical axis of the joists.

  • Squash blocks are cut 1/16" taller than the height of the I-joist so that the blocks, not the joists, carry the load. That is to say, the extra 1/16" will appear at the top, not bottom, of the I-joist.

  • Secure squash blocks by nailing an 8d (0.131" x 2-1/4") into the top and bottom flange of the I-joist.

  • Note: squash blocks are not a replacement for proper blocking, and blocking must be used under most circumstance below load-bearing walls.


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