What thickness of plasterboard do I need and how far apart do the screws go?

Board thickness, framing spacing and fixing centres are one system. Getting any one of them wrong shows up as sagging, cracked joints or popped screws, and all three are easy to get right.

What you'll need

• drywall screws
• drill driver with a depth-stop nose
• tape measure and pencil
• board lifter for ceilings (optional)

Step by step

1. Match thickness to framing spacing.Twelve and a half millimetre board suits studs and joists at up to 600mm centres. Nine and a half millimetre board is only appropriate at closer centres, typically 400mm, and mostly on ceilings.
2. Use thicker or doubled board where performance is needed.Fifteen millimetre board, or two layers with staggered joints, where fire, acoustic or impact performance is specified. Two thinner layers usually outperform one thick one for sound.
3. Choose the right screw.Drywall screws with a bugle head that sets flush without tearing the paper. Coarse thread for timber, fine thread for metal studs — they are not interchangeable.
4. Get the screw length right.Roughly board thickness plus 25mm of penetration into timber. So 38mm screws for 12.5mm board on timber studs is the common combination.
5. Set the fixing centres.About 300mm apart on walls and 230mm on ceilings, following the line of each stud or joist. Ceilings need closer centres because the board is loaded by its own weight continuously.
6. Keep fixings back from the edges.At least 10mm from a cut edge and 13mm from a bound edge. Screws too close break the edge out and the fixing does nothing.
7. Set the screw depth correctly.The head should just dimple the paper without tearing it. A torn face means the screw is holding on nothing. A depth-stop nosepiece on the driver makes this consistent.
8. Stagger the joints.Do not line up board ends across the framing in a continuous line. Staggering means no single joint runs the full length, which greatly reduces cracking.
9. Land every board edge on framing.An unsupported edge will crack along the joint. Add noggins between studs where a horizontal joint falls.
10. Board ceilings before walls.The wall boards then support the ceiling board edges, which is both easier and stronger.
11. Leave a small gap at the floor.Around 10mm, so the board is not wicking moisture off the floor slab and so it can be levered up tight to the ceiling.

Tips

• A depth-stop nosepiece on the driver costs very little and stops the single commonest boarding error — screws driven through the paper face.
• Ceiling fixings closer than wall fixings, always. Gravity works on a ceiling continuously.
• Stagger the board joints. Continuous joints across a wall are where cracks appear.

Common mistakes

• Driving screws through the paper face — The paper liner is what carries the fixing. Once it is torn, the screw is holding in gypsum core alone, which is weak, and it will pop through the finish later.
• Leaving a board edge unsupported between studs — The joint has nothing behind it, so it flexes and the tape and filler crack along it within months. Add a noggin.

If it doesn't work

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