Flooring, Ceilings, Partitions and Interior Finishes
This section covers timber flooring, joists, decking, ceiling systems, partition framing, and finish quality. Expect questions on spacing, ventilation, expansion gaps, fixing patterns, and the difference between structural and non-structural framing.
Core rules
- Floor joists must be sized and spaced to the design; do not overspan. Provide ventilation beneath suspended timber floors.
- Leave an expansion gap at timber floor perimeters and around obstructions; do not jam boards tight to walls.
- For tongue-and-groove flooring, secret-nail or blind-nail through the tongue and keep joints staggered.
- Ceiling battens and grid members need fixing at the manufacturer’s spacing; board joints should be supported.
- Partition studs are typically set at consistent centres with noggings for stiffness and edge support; fire and acoustic ratings depend on the complete system, not just the board.
- Fix finishes only after the substrate is dry, secure, and within tolerance.
Worked example
A room is 4.8 m long and floor joists are required at 400 mm centres. Number of spaces = 4800 ÷ 400 = 12. Number of joists including both end joists = 12 + 1 = 13. If the design also requires a trimmer around a stair opening, add separate trimmer and trimming joists. The reasoning: count spaces first, then add one to get the number of joists, and account for openings separately.
Traps
- Fitting floor boards tight to walls with no expansion gap.
- Overspanning joists or notching them excessively for services.
- Fixing ceiling boards to unsupported joints.
- Ignoring ventilation under a suspended timber floor.