What is required for a 3 feet 8 inches by 4 feet long floor opening near the center of a wood-framed span?

To properly support a floor opening of 3 feet 8 inches by 4 feet long in a wood-framed span, a single header with double trimmers is the most appropriate requirement. The function of the header is to carry the load above the opening and transfer it to the adjacent framing. In the case of a larger opening, additional support in the form of trimmers is necessary to help distribute the load effectively.

Using a single header ensures that there is enough strength to span the opening, while double trimmers provide additional support on either side of the header. This setup helps to reinforce the structural integrity of the framing around the opening, accommodating the load from both the framing above and any additional weight that may be placed on the floor.

While a double header with a single trimmer could also provide adequate support, the need for a double trimmer with a single header is specifically designed to maximize the opening's structural stability. This configuration allows for balanced load distribution around the opening, reducing the risk of sagging or failure in the framing system.