What is the maximum distance that a header made of two 2x12s can span across an opening with a clear span floor, roof and ceiling above it?

What is the maximum distance that a header made of two 2x12s can span across an opening with a clear span floor, roof and ceiling above it?

• A. 8 feet 1 inches
• B. 7 feet 9 inches
• C. 9 feet 9 inches
• D. 8 feet 6 inches

Answer: (B)

Header span capacity comes from how much bending and deflection the built-up member can carry under the loads coming from above. When a header sits over an opening with a floor joist span (clear span) and the roof/ceiling above, it has to transfer both floor loads and roof loads down to the supporting walls. That makes the required strength and stiffness of the header important. A double 2x12 built-up header provides considerable depth and stiffness, but its capacity is still limited by bending strength under the combined dead and live loads. With a floor above and the roof/ceiling, code-approved tables set a maximum span for this header size to keep bending and deflection within allowed limits. For this configuration, that maximum span is seven feet nine inches. Spans longer than that would exceed the header’s design capacity, so a larger header or additional supports would be needed. So the longest safe span for two 2x12s under these conditions is seven feet nine inches. The other options would be too long for this header size under typical residential loads.

Header span capacity comes from how much bending and deflection the built-up member can carry under the loads coming from above. When a header sits over an opening with a floor joist span (clear span) and the roof/ceiling above, it has to transfer both floor loads and roof loads down to the supporting walls. That makes the required strength and stiffness of the header important.

A double 2x12 built-up header provides considerable depth and stiffness, but its capacity is still limited by bending strength under the combined dead and live loads. With a floor above and the roof/ceiling, code-approved tables set a maximum span for this header size to keep bending and deflection within allowed limits. For this configuration, that maximum span is seven feet nine inches. Spans longer than that would exceed the header’s design capacity, so a larger header or additional supports would be needed.

So the longest safe span for two 2x12s under these conditions is seven feet nine inches. The other options would be too long for this header size under typical residential loads.