Most South African houses have a ceiling of gypsum board fixed to timber branders, which are nailed or screwed across the underside of the roof trusses. Gyproc’s RhinoBoard installation and estimating guide gives the sizes and spacings, and this guide follows it.
Branders
Branders are small timber battens fixed at right angles to the trusses. Their size depends on how far apart the trusses are:
| Truss spacing | Brander size |
|---|---|
| Up to 1,000 mm | 38 × 38 mm |
| 1,001 to 1,200 mm | 38 × 50 mm (50 mm vertical) |
| 1,201 to 1,400 mm | 50 × 75 mm |
| Over 1,400 mm | Consult an engineer |
So a tiled roof with trusses at 760 mm takes 38 × 38 mm branders, and a sheeted roof with trusses at 1,200 mm takes 38 × 50 mm on edge.
Brander centres
How close the branders are depends on the board and the finish:
| Board and finish | Brander centres |
|---|---|
| 6.4 mm RhinoBoard with M-strip joints | 400 mm |
| 6.4 mm, flush plastered | 300 mm |
| 9.5 mm (now sold as 9 mm), flush jointed | 500 mm |
| 9.5 mm, flush plastered | 400 mm |
Boards
6.4 mm RhinoBoard comes 900 or 1,200 mm wide and 2,700 to 4,200 mm long in 300 mm steps. The thicker board comes 1,200 mm wide and 2,400 to 3,600 mm long. Boards are fixed with their long side across the branders, end joints are staggered by at least 300 mm, and boards are screwed or nailed with clout nails at 150 mm centres along every brander.
Choosing board lengths
Pick a board length that suits the room so you have fewer end joints and less waste. A room 3.6 m wide can take 3.6 m boards end to end across it with no joints; a 4.5 m room will need joints, and Gyproc asks for end joints to be staggered by at least 300 mm, so plan the layout before ordering. Shorter boards are easier to handle in a small roof space, but every extra joint means more taping and more risk of a visible line.
Counting a ceiling
Worked example: a 4.5 × 3.6 m room with a 6.4 mm M-strip ceiling, trusses at 760 mm.
- Area = 16.2 m². With 1,200 × 3,000 mm boards (3.6 m² each) and a little for cutting, about 5 boards.
- Branders at 400 mm centres across the 3.6 m width: 3.6 ÷ 0.4 = 9 spaces, so 10 rows, each running the 4.5 m length of the room. That is 45 m of brandering, about 48 m with 5% extra.
- Brander size: 38 × 38 mm for trusses at 760 mm.
- Screws at 150 mm along each brander: 10 × 4.5 ÷ 0.15 = 300 screws.
The brandered ceiling calculator works this out with your choice of board, finish and truss spacing, including the wastage from board lengths. For walls and partitions in RhinoBoard, see the drywall partition calculator.
Finishes and cornices
An M-strip ceiling has visible strips over the board joints and is the quickest to finish. A flush-jointed ceiling is taped and filled for a smooth, seamless look. A flush-plastered ceiling gets a skim of plaster over the whole board, which needs the branders closer together. Cornices are fixed at the wall-to-ceiling joint to finish the edge; count them by the room perimeter.
Before you close the ceiling
- Level the branders from the lowest point, packing them where needed, so the ceiling is flat.
- Run electrical cables and fit supports for lights before the boards go up. Fix light fittings to branders, not to the board alone.
- Lay or plan the ceiling insulation. SANS 10400-XA sets the R-value the roof must reach; see ceiling insulation under SANS 10400-XA.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check SANS 10400 (the National Building Regulations) and your local municipality’s building control officer for your project.