A lap joint is one of the many joints used to join two pieces of wood together. With this type of joint, this is done by overlapping the wood and fastening them together. They are made in two categories — the full and the half — and both 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 are used in framing and in cabinetry, and in addition, variations 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, but 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. This type of 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 is the cross joint, which is a form of the half-lap and is made 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 joint that cannot be easily pulled apart.
