What type of joint is used for double top plates at wall corners?

A lap joint is the correct choice for double top plates at wall corners because it provides a strong connection by overlapping two pieces of material. When constructing walls, especially at corners where two frame sections meet, the lap joint allows for a continuous transfer of load and added structural support. This overlapping technique reinforces the joint, making it less susceptible to shear forces that can occur at corner areas, which are often prone to stress.

While other joint types may have their specific uses, such as butt joints providing a simple end-to-end connection or scarf joints used for lengthening material by overlapping them at an angle, they may not provide the same level of strength and reliability needed in this particular application. Mismatch joints, while occasionally appearing in various forms of construction, do not offer the necessary structural integrity required in a corner connection of wall framing.