What Is a Lap Joint?

A lap joint is one of the many joints used to join two pieces of wood together. With a lap joint, this is done by overlapping the wood and fastening them together. There are two categories of lap joints in existence — the full and the half — and both of these are used in a slightly different way. The full lap joint is contrasted from the half-lap in the amount of material that is used to make the joints. Different types of these joints are used in framing and in cabinetry. In addition, variations on the joint exist and include the cross, the dovetail, and the mitred.

If two pieces of wood are joined without any material being removed, a joiner will have made a full lap joint. The thickness of this joint will be the sum of the thickness of both wood pieces. A full lap requires fasteners in order to stay together and offers no resistance to racking. However, it does partly resist twisting and shearing. This joint can be used in temporary framing and in the construction of some timber frames.

A half-lap joint can be used in construction and cabinetry. To make this joint, half the thickness of the material is removed from the two pieces of wood to be joined. After this, the wood is fitted together with a resulting joint that is the same thickness as the rest of the wood. A half-lap joint can be reinforced by dowels or by fasteners. It offers some resistance to racking and, when it uses fasteners, to twisting and shearing.

One variation of the lap joint is the cross joint. It is a form of the half-lap joint and occurs when one piece of wood crosses over the middle of one or both pieces. In this joint, the two pieces of wood are joined together at a right angle. If one of the pieces stops at the joint, the joint is called a Tee lap. Dovetail laps are a type of tee lap that can be used when the joiner desires to use a lap joint that cannot be easily pulled apart.

Written by M.R. Anglin