Where should squash blocks (web blocking) be found in a wood I-Joist floor system?

In a wood I-Joist floor system, squash blocks (or web blocking) are crucial for providing additional support and transferring loads from above structures to the joists efficiently. The correct placement of squash blocks is primarily at the bearing ends and under any load-bearing walls that are situated above, particularly where there are supporting girders below.

When placing squash blocks in this manner, they help in redistributing the load across a broader area of the joist, ensuring the structural integrity of the floor system. By placing them at bearing ends, the support from the foundation or walls is effectively transferred, while blocking under load-bearing walls helps manage concentrated loads that would otherwise compromise the strength and functionality of the I-Joist system.

The context of the other choices highlights locations that are not as critical for squash block installation or contribute less significantly to the overall structural support that the blocks provide. Therefore, focusing on bearing ends and load-bearing walls with supporting girders ensures the design remains robust and effective for standard construction practices.