What is a half-lap joint?
A half-lap joint is a woodworking joint in which half the thickness is removed from both workpieces so that they overlap and together form the original thickness. It is a simple and widely used joint for crosses, corners and T-junctions.
How does it work?
From each workpiece, exactly half of the height is removed at the location of the joint. The two workpieces then fit together like a puzzle, flush on flush.
The difference from a scarf joint: with a half-lap, the workpieces cross or meet at a corner; with a scarf joint, they are extended in the same direction.
Types of half-lap joints
| Type | Description | Application |
|---|---|---|
| Cross half-lap | Two beams cross each other | Framing, structural frames |
| Corner half-lap | Two beams meet at a corner | Frames, window frames |
| T half-lap | One beam joins another halfway along | Intermediate rails, framework |
| Angled half-lap | At an angle (not 90°) | Braces, angled connections |
When do you use a half-lap?
- Framing — Where horizontal and vertical rails cross
- Frames — Simple window and door frames
- Garden furniture — Picnic tables, benches
- Structural frames — Temporary frames, jigs
A half-lap is less strong than a mortise and tenon joint, but much simpler to make.
Making a half-lap joint yourself
Tools
- Saw (hand saw or circular saw)
- Chisel
- Try square
- Caliper or ruler
Steps
- Mark the width of the crossing workpiece on the other workpiece
- Draw the lines — Width and depth (half the height)
- Make multiple saw cuts — Within the marked area, to half depth
- Chisel out the waste — Break out the saw cuts with a chisel
- Flatten — Level the surface with the chisel
- Test fit — Both workpieces should sit flush together
- Join — Glue, screws or bolts
Tip with a circular saw
Set the cutting depth to exactly half the beam height. Make multiple cuts side by side within the marked area. Break out the remaining lamellae with a chisel — fast and reasonably accurate.
Half-lap vs. other joints
| Half-lap | Mortise & tenon | Dowel | |
|---|---|---|---|
| Difficulty | Low | Medium-high | Low |
| Strength | Moderate | Very strong | Strong |
| Visible | Yes (both sides) | Optional | No |
| Weakening | Yes (50% wood removed) | Minimal | None |
The disadvantage of a half-lap: you remove half the wood at the joint location, which weakens the workpiece there.
Related terms
- Mortise and tenon joint
- Scarf joint
- Dowel
- Dovetail joint