How do I overboard a ceiling with plasterboard?

Overboarding is usually the right answer for a tired ceiling: it avoids taking down a lath and plaster ceiling, it encapsulates a textured coating without disturbing it, and it produces a flat surface without the extraordinary mess of demolition. It is also considerably harder than boarding a wall, because every board has to be held overhead in exactly the right position while it is fixed.

Safety

What you'll need

• Plasterboard, 9.5mm or 12.5mm
• Drywall screws long enough for both layers plus 25mm into the joists
• Joist detector, and a cable detector
• Panel lifter or board hoist — hired
• Goggles, P3 mask, gloves
• Chalk line
• Plasterboard saw and knife
• Scrim or paper tape and jointing compound

Step by step

1. Check the existing ceiling is fit to be covered.Tap it. A sound ceiling that is merely ugly is a good candidate. One that is sagging, bulging, wet or drumming over large areas should come down instead, because you would be screwing new board into a layer that is about to let go.
2. Check the joists can take it.A layer of 12.5mm plasterboard adds real weight across the whole ceiling. On an ordinary domestic ceiling with sound joists this is not usually a problem, but on an old lath and plaster ceiling — which is already heavy — or where the joists are undersized, spanning far, or already carrying a boarded loft above, it is a question worth putting to a structural engineer rather than assuming.
3. Find the joists and mark them on the walls, not the ceiling.A detector, confirmed with fine pilot holes. Mark the centre of each joist on the wall at both ends of the run, in pencil, and snap chalk lines between them across the existing ceiling. The wall marks are what you will use once the ceiling is covered, so they matter most.
4. Note the joist direction and spacing.New boards run at right angles to the joists, so the long edge of each sheet crosses several. Common domestic spacings are 400 or 600mm, and the board and screw pattern follow from that.
5. Isolate and deal with the light fittings.Take pendants and roses down, isolate the circuits, and leave the cables safely accessible where you can find them. Downlights need their positions marked and re-cut, and their fire and insulation requirements re-considered once the ceiling build-up changes.
6. Hire a board lifter.A panel hoist holds the sheet flat against the ceiling while you fix it, positions it precisely, and removes the entire physical struggle. It is the difference between a job that is possible alone and one that is dangerous with two people.
7. Start in a corner and work across.Butt the first sheet tight into the corner, with the long edge across the joists and the ends landing on the centre of a joist. Fix along each joist line at roughly 150mm centres, working from the middle of the board outwards so it is held flat.
8. Stagger the end joints.Like brickwork. Every end joint has to land on the centre of a joist, and no two rows should line up. Continuous joints across a ceiling are where cracks appear.
9. Add noggins where an edge lands in mid-air.Any board edge without timber behind it will move and crack. Where the layout forces an unsupported edge, fix a noggin between the joists through the old ceiling before you board over it.
10. Leave a small gap at the perimeter and seal it.Two or three millimetres round the edges, filled with a flexible sealant or covered by coving. It stops the board binding as the building moves and it closes the air path.
11. Tape or skim to finish.Tape and joint over tapered-edge board for a paintable finish, or scrim and skim for a plastered one. A ceiling shows every defect under a light, so this is where care pays off.
12. Refit the details forward.Coving, ceiling roses, smoke alarms and downlights all come back at the new level. Downlight housings need enough depth above them, and any fire or insulation detail has to be reinstated properly.

Tips

• Ceilings are where 9.5mm board is genuinely worth considering over 12.5mm — it is a third lighter to lift, and on an overboard it is supported continuously by the ceiling underneath.
• Cut boards slightly under size rather than tight. A sheet that has to be forced into position overhead is a sheet you will drop.
• If the ceiling has coving, decide whether to remove it and re-fit it, or board up to it and lose the bottom of the profile. Removing plaster coving intact is difficult; polystyrene and duropolymer coving is usually easier to replace than to save.
• Do the tape-and-joint from a proper platform rather than a stepladder. Working overhead at full stretch for hours is what makes ceilings look bad.

Common mistakes

• Fixing into the old ceiling rather than the joists — A ceiling holds its own weight in the worst possible direction. Screws that stop in old plaster or old board are holding nothing, and the failure mode is a sheet of plasterboard falling on someone.
• Overboarding a sagging ceiling — You are adding load to something that has already told you it cannot carry what it has.
• Using screws that are too short — The calculation is new board plus old ceiling plus old plaster, plus 25mm into the joist. On lath and plaster that total is often 65 to 75mm, which surprises people.
• Working alone without a lifter — A 12.5mm sheet is heavy, unwieldy and flexible, and holding one overhead while trying to drive a screw is how people injure their shoulders and drop boards on their heads.

Questions people ask