Every application where solid sawn lumber is used in conjunction with engineered wood must be looked at very carefully with respect to the material’s moisture content at the time of construction. The safest alternative is to not mix engineered wood with solid sawn lumber in any situation where load sharing might be an issue.

APA EWS I-joists and APA EWS Rim Board products are made in 9-1/2-, 11-7/8-, 14-, and 16-inch net depths. It is no accident that these sizes are not compatible with, and are larger than, actual depths of traditional lumber joists and beams. There are many applications where other elements are used in conjunction with I-joists for the express purpose of transferring load through a floor system without overloading the joists. Some examples are blocking at an interior bearing wall and rim or starter joists. In these cases, the vertical load from the structure above is transferred through the floor into the structure below by way of direct bearing on the blocking, rim or starter joist.

Because the load is transferred in direct bearing, it is essential that the blocking, rim or starter joist be the same height as the floor joist. When I-joists are used, solid sawn lumber should not be used without careful consideration of the consequences of shrinkage. Shrinkage by as little as 1/8 inch can be enough to transfer the vertical loads from above directly to the I-joists, thus inducing possible bearing or reaction overload conditions. The solution is to use engineered wood products for these applications. They are manufactured in the correct depths and have the same dimensional stability properties as I-joist.

The same is true of lateral loads, such as those caused by wind and seismic events. A small gap between floor sheathing and the rim joist or blocking panel can have a negative impact on the performance of the structure. The potential slip at this location can have a great impact on the deformation of the structure. Such deformations can result in increased damage to the non-structural components of the building, such as drywall, windows and doors, cabinets and interior and exterior finishes. If the deformations are excessive, the structure may be irreparable.

For more information on this topic, reference the following APA publications:

• Builder Tips: I-Joist Blocking, Form A750
• I-Joist Construction Details - Performance Rated I-Joists in Floor and Roof Framing, Form D710
• APA Performance Rated I-Joists, Form Z725
• APA Performance Rated Rim Boards, Form W345
• Technical Topics: APA Wood I-Joists and APA Rim Board, Form TT-022