What is the standard thickness of the spacer used to form headers by nailing two members together?

The standard thickness of the spacer used to form headers by nailing two members together is typically 3/4". This thickness allows the header to properly align with standard dimensional lumber, which is usually 1½” thick when considering the nominal dimensions. Using a spacer of 3/4" accommodates the required gaps and ensures that the header can effectively support loads and maintain structural integrity.

While there are various thicknesses of wood available, a 1/2" spacer would generally not provide sufficient support or alignment for most header applications. Similarly, a 1" thickness might be overly cumbersome, potentially leading to misalignment or excessive height in the framing, while a 1/4" thickness would likely be inadequate for structural needs. The 3/4" option is the most commonly used and is aligned with standard building practices, making it the most appropriate choice for forming headers.