APA - The Engineered Wood Association
Squash blocks are required in conventional platform construction where loads from above are transferred down through the floor into the wall or foundation below. This occurs where load-bearing walls fall on floors or posts supporting headers are located within the walls. Beneath these wall and point loads, the I-joists usually do not have enough interior reaction or exterior reaction capacity remaining to safely transfer these loads without risking a web-bearing failure. The solution is to place extra load-carrying members in line with these loads and insure that these squash blocks carry the load and the I-joists do not.