Which woodworking joint should I use?
Butt, housing, half lap and mortise and tenon compared on strength, difficulty and what each is actually for.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 3 min
Short answer
Match the joint to the load, not to your ambition. Butt joints with screws are fine for anything hidden or lightly loaded; housings carry shelves; half laps make flat frames; mortise and tenon is what you use when a joint has to resist being racked, like a chair or a table.
Beginners tend to choose a joint by how impressive it looks. The useful question is what the joint has to resist — pulling apart, being pushed sideways, or carrying weight downwards.
Step by step
- Work out what the joint has to resist.Downward load, like a shelf. Pulling apart, like a drawer front. Racking, meaning being pushed out of square, like a chair or a door frame. Different joints answer different questions.
- Use a butt joint where it is hidden and lightly loaded.Two square ends screwed or nailed together. Weak in itself, but with screws or pocket screws it is entirely adequate for carcass backs, battens and jigs.
- Use a housing for shelves.A trench cut across one board that the shelf sits into. It stops the shelf sagging out of its socket and it carries downward load without relying on the glue at all.
- Use a half lap for flat frames.Half the thickness taken from each piece so they overlap flush. Big face-grain glue area, easy to cut with a saw and chisel, and good at resisting racking.
- Use a mortise and tenon where the frame must stay square.Chairs, tables, doors and gates. The tenon inside the mortise resists racking in a way glue on a flat face never can, which is why the joint has survived several thousand years.
- Consider dowels or biscuits as a shortcut.They add alignment and a little mechanical strength to a butt joint. Useful for carcass work, but they are not a substitute for a mortise and tenon under racking load.
- Be honest about the accuracy each needs.A joint you cut badly is weaker than a simpler joint you cut well. A crisp housing beats a sloppy mortise and tenon every time.
- Practise on offcuts before committing.Cut two or three of the joint in scrap of the same thickness. It is quicker than remaking a component.
Tips
- Racking load is the one that decides most joints. If the frame must stay square, you need a mortise and tenon.
- A well-cut simple joint beats a badly cut clever one.
- Screws are not cheating. Half of professional carcass work is butt joints with screws under a veneer of neatness.
Common mistakes
- Choosing the joint by how impressive it looks — Dovetails on a shelf carrying nothing are wasted effort, and a butt joint on a chair leg fails within a year. The load, not the appearance, should decide.
- Cutting the joint straight into the good timber — The first attempt at any new joint is the practice one. Cutting it in scrap first costs ten minutes and saves remaking a component.
If it doesn't work
Shelf sagging out of its supports
Cause: Butt joint carrying downward load — Fix: Cut a housing, or add a batten underneath the shelf.
Frame goes out of square when pushed
Cause: No racking resistance — Fix: A half lap, mortise and tenon, or a diagonal brace at the back.
Joint loose after cutting
Cause: Cut to the wrong side of the line — Fix: Always cut in the waste and pare back to the line. A tenon can be shimmed with veneer as a rescue.
Mortise walls blown out
Cause: Too close to the end of the workpiece — Fix: Leave a horn of extra length beyond the mortise and trim it off after assembly.
Questions people ask
Which joint is strongest?
Of the common four, mortise and tenon, because the tenon physically resists the joint being racked or pulled apart rather than relying on a glue film. Half lap is next, then housing, then butt.
Are dowels good enough?
For carcass alignment and light loads, yes. For anything that gets pushed sideways repeatedly, such as a chair, dowels alone tend to work loose over time.