Ceilings
Ceiling boards across the joists: supports per board, end and field screws
- where
- supports under each board
- board length across the supports (mm)
- joist or ceiling section centres (mm)
- screws on each end support
- board width (mm)
- screw centres at board ends (mm)
- screws on each intermediate support
- screw centres in the field (mm)
- screws per board
- screws per m²
Explain this equation
For ceiling boards laid with their long edges across the joists or MF5 sections, this gives the supports under each board and the screws needed at the published end and field spacings.
ns is the number of supports under a board of length Lb at centres s. ne is the screws along each end support at the tighter end spacing e; nf is the screws on each intermediate support at the field spacing c, across the board width Wb. Nb adds the two ends and the intermediate supports. Nm divides by the board area to give screws per m².
Rounding down for supports means the board ends land on a joist; rounding up for screws keeps every gap at or below the maximum, and the +1 puts a screw near each edge. Dividing Wb × Lb by 1,000,000 turns mm² into m².
Sense check: a 1200 × 2400 board on 400 mm joists sits on 7 supports and takes about 53 screws, about 18 per m².
Watch out: perimeter boards also need 150 mm centres along the wall edge.
For ceiling boards fixed with their long edges across the joists or MF5 sections: how many supports each board sits on, and the screws at the tighter end spacing plus the field spacing.
Enter your values to see the result.
Good to know
Fix ceiling boards with the long (bound) edges at right angles to the joists or MF5 ceiling sections, ends on a support and end joints staggered. British Gypsum and NHBC fix ceilings at 230 mm maximum centres in the field, reducing to 150 mm at board ends and perimeters; screws at least 10 mm from bound edges and 13 mm from cut edges. NHBC Table 6: 12.5 and 15 mm boards on 450 mm centres need only perimeter noggings, at 600 mm they need intermediate noggings too; 9.5 mm board is limited to 400 mm without noggings; 19 mm plank spans 600 mm. The fourth output gives that no-intermediate-nogging limit for the thickness entered.
Common mistake
Running ceiling boards parallel to the joists, which leaves long edges unsupported and halves the number of supports, or screwing the ends at the 230 mm field spacing.
Limits
One board, long edges across the supports; perimeter boards also get 150 mm centres along the wall edge, which this does not add. Fire-rated and multi-layer ceilings follow the system specification for each layer.
Sources
- NHBC Standards 9.2.4 Dry lining (Table 5 wall support centres, Table 6 ceiling support centres and noggings, Table 7 screw centres, Table 8 screw lengths)
- British Gypsum, GypCeiling MF GCMF-1L-WB12 specification (hangers and MF7 at 1200 mm, MF5 at 450 mm, screws 230 mm reducing to 150 mm at board ends and perimeters, 30 kg/m² maximum load)
- British Gypsum, White Book: GypCeiling MF (suspension points at 1200 mm centres each way; MF5 ceiling sections at 450 mm for Gyproc boards; MF7 centres 600–1200 mm by load, Table 1; boards fixed perpendicular to MF5; MF6 perimeter channel at 600 mm centres)
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the manufacturers’ system and product data, BS 8212, BS EN 13914 and Building Regulations. Coverage rates vary by product, background and thickness. Check prices, VAT and CIS rules with your own records and HMRC.