What is the maximum distance that a header of two 2 x 12's can span across an opening with a clear span floor, roof, and ceiling above it?

The maximum distance that a header made of two 2 x 12s can effectively span across an opening with a clear span floor, roof, and ceiling above it is determined by several factors, including the load it must support and the species and grade of wood used. Typically, for a double 2 x 12 header, the span can vary depending on the load conditions, but for residential construction, a common guideline established by building codes and structural engineering principles indicates that it can safely span up to approximately 7 feet 9 inches under typical loading conditions.

This length allows the header to distribute loads from the framing above effectively while also minimizing the risk of sagging or failure. The spans provided in the other options exceed standard guidelines for two 2 x 12 headers, which typically would lead to insufficient structural support for the loads above, thus emphasizing the importance of adhering to established building practices and regulations.

Therefore, the correct answer of 7 feet 9 inches aligns with standard practices in structural framing, reflecting the capabilities of two 2 x 12 headers in supporting typical residential loads.