Q. Framers in our area typically splice long hip and valley rafters with the scarf joint shown in the illustration. Is this adequate to support the roof load?

A.Robert Randall responds: No, the scarf joint you show is not adequate to support typical roof loads on a hip or valley rafter. These members must be able to function as bending beams carrying substantial vertical loads.

Hip and valley rafters should never be compromised by such a weak splice. If splicing is required, secure a sister that runs at least four or five feet on either side of the joint. This splice should be capable of developing the full bending strength of a continuous member. Spike the overlapping piece together with plenty of well-placed nails, or better yet, with carriage bolts, as shown.

An even better alternative would be to use engineered lumber (such as Microlam LVL), which is available in the required lengths. Although this material will cost more, it will offset, at least in part, the labor cost of making a splice. And the end result will be superior.

Robert Randall, P.E., is a structural engineer in Mohegan Lake, N.Y.