What is the required thickness of headers and trimmers when their length exceeds 4 feet?

When headers and trimmers exceed a length of 4 feet, building codes require that they be constructed as double members. This means using two pieces of lumber instead of a single piece.

The reasoning behind this requirement is primarily structural. Longer spans necessitate greater strength and support to bear the weight of the load above them. By using double members, the load is distributed more evenly, which enhances the overall integrity of the framework and reduces the risk of sagging or failure over time.

Using double headers helps to prevent issues with framing, such as excessive deflection or bending, that can occur when single pieces of lumber are used for long spans. It ensures that the installation adheres to safety standards and building regulations, ultimately contributing to the longevity and stability of the structure.