Cross lap joints are a great solution when you want to create clean, continuous lines in a timber frame. The edges of the joint are completely flush. They make it almost appear that the timbers are magically connected. To create a cross lap joint, you cut halfway through the width of both timbers that you are connecting. They slide together into an extremely solid joint.
Cross Lap Joint
The cross lap joint usually occurs in the middle of one or both timbers, rather than at the end. In this example, the cross lap also occurs on top of a post. So in addition to the tie beam and the plate being cut halfway through to nest together, the tie beam has a mortise cut into it for the tenon on the post to fit into. These two timbers are secured with pegs, and then the assembly is inserted into the plate and secured with structural screws.
Cross Lap Corner Joint
Just as it sounds, the cross lap corner joint occurs at an outside corner of a timber frame, where a tie beam and a plate meet. This example also happens to fall on top of a post. So as in the cross lap joint, the mortise on the tie beam fits into the tenon on the post and is secured with oak pegs. Then the plate snugs down on top of that assembly and is secured with structural screws.
Cutting a Cross Lap Joint
In order to get the parts of a cross lap joint to nestle together on a parallel line, you need to cut exactly half the depth of the timbers. The outermost cuts are the “perimeters.” They create the edges of the cross lap, so they need to be tight and precisely measured. If you take care with your measuring and cutting, your cross lap joint will look like the two timbers pass wondrously through one another.