A floor opening of 3'8" by 4' near the center of a wood-framed span requires which configuration?

A floor opening of 3'8" by 4' near the center of a wood-framed span requires which configuration?

• A. Single header and double trimmer
• B. Double header and single trimmer
• C. No header needed
• D. Two headers

Answer: (A)

When you open a floor in a wood-framed span, the loads carried by the joists must be transferred around the opening rather than left unsupported. A header across the opening acts as a beam to take the loads from the joists that cross the opening, and trimmer joists on the ends transfer those loads from the adjacent joists into the header and down into the surrounding structure. For an opening about 3'8" wide (less than 4 feet) near the center of the span, a single built-up header across the opening provides the necessary support. One trimmer on each end carries the ends of the joists that are cut to form the opening, delivering their loads into the header. This arrangement is enough to support the floor above without overcomplicating the framing. Two headers would be more than required for this size, and omitting a header is not acceptable because the loads must be carried around the opening.

When you open a floor in a wood-framed span, the loads carried by the joists must be transferred around the opening rather than left unsupported. A header across the opening acts as a beam to take the loads from the joists that cross the opening, and trimmer joists on the ends transfer those loads from the adjacent joists into the header and down into the surrounding structure.

For an opening about 3'8" wide (less than 4 feet) near the center of the span, a single built-up header across the opening provides the necessary support. One trimmer on each end carries the ends of the joists that are cut to form the opening, delivering their loads into the header. This arrangement is enough to support the floor above without overcomplicating the framing. Two headers would be more than required for this size, and omitting a header is not acceptable because the loads must be carried around the opening.