How do I find studs and joists reliably?

Stud detectors are useful and routinely wrong. Using one well means treating its reading as a hypothesis and confirming it another way.

Safety

What you'll need

• A detector, ideally with a deep-scan mode
• A strong magnet on a string
• A thin bradawl or a 2mm drill bit

Step by step

1. Understand what you are looking for.Studs are usually 400 or 600mm apart in a modern house, and often irregular in an older one. Joists are typically 400mm centres. Knowing the spacing lets you predict rather than hunt.
2. Calibrate on a clear area.Most detectors need to start over an empty part of the wall. Starting over a stud gives readings that are wrong everywhere.
3. Sweep slowly.Much slower than feels natural. Moving quickly is the commonest cause of a missed stud or a false edge.
4. Find both edges, then take the centre.Sweep left to right and mark where it triggers, then right to left and mark again. The centre between the two marks is the middle of the stud, which is where you want to fix.
5. Check the spacing makes sense.Find one stud, then measure 400 and 600mm along and check. If readings do not fall at a regular spacing, some of them are false.
6. Use a magnet to find the screws.A strong magnet dragged over the wall locates the plasterboard screws, which are driven into the studs. It is slower than a detector and far more reliable.
7. Look for evidence you can see.Screw dimples under paint in raking light, the edge of a board, a socket box, or the pattern of nails on a skirting board.
8. Tap along the wall.A hollow sound between studs, a duller sound over one. Crude but effective, and it confirms or contradicts the detector for free.
9. Treat cable zones as live regardless.Cables run vertically and horizontally from every socket and switch, and in the 150mm bands at the top of walls and in corners. A detector saying clear does not change that.
10. Use the deep scan mode carefully.It reads further but produces more false positives from pipes, foil-backed board and metal framing. Use standard mode first and deep scan only to check.
11. Watch for metal framing.In some newer builds and most commercial conversions, the studs are steel. A magnet finds them easily, and they need completely different fixings.
12. Confirm with a small pilot hole.A 2mm bit or a bradawl, in a spot that will be covered. Resistance behind the board means timber; going straight through means a void.
13. Mark the line, not just the point.Once you have a stud, pencil its vertical line. It saves rescanning when you want a second fixing higher or lower.
14. Check from the other side where possible.In a loft or under floorboards you can often see the joists directly and measure their position from a fixed point, which beats any detector.

Tips

• A magnet finding plasterboard screws is more reliable than most detectors and costs almost nothing.
• Mark both edges and drill the centre. Fixing at the edge of a stud gives you half a grip.
• Check the spacing is regular at 400 or 600mm. Irregular readings mean some are false.

Common mistakes

• Trusting a detector near sockets and switches — Detectors find cables far less reliably than timber, and the area around outlets is exactly where cables run. Isolate the circuit if you must drill there.
• Calibrating the detector while it is over a stud — It sets its baseline from that reading, so it then reports the empty wall as solid and the stud as empty. Always start over a clear area.

If it doesn't work

Questions people ask