Roof framing to NZS 3604

How it is worked out

1. 1

   Rafters

   3.6 m at 900 mm spacing in a High wind zone, the table's spans times 1.1: 290 × 45, spanning up to 3.63 m, fixing E; or 190 × 70, spanning up to 3.85 m, fixing E; or 190 × 90, spanning up to 4.18 m, fixing E

   Why A rafter carries the roof from the wall plate up to the ridge, so its size follows its span, how far apart the rafters are and how heavy the roof is. Wind lifts a roof, so the zone's factor shortens the spans.

   NZS 3604:2011 10.2.1.3, Table 10.1(a)

2. 2

   Purlins

   70 × 45 over supports at 900 mm spacing, High wind zone: 1400 mm (1.4 m) spacing with fixing U; 1200 mm (1.2 m) spacing with fixing T; 900 mm spacing with fixing T

   Why Purlins carry the roofing across the rafters or trusses. On the flat they span the rafter or truss spacing, and the wind zone sets how far apart they go and how they are fixed; on edge they span between walls.

   NZS 3604:2011 10.2.1.16, Table 10.10

   70 × 45 purlins on the flat over supports at 900 mm spacing, by wind zone, Table 10.10

   Wind zone	Spacing and fixing
   Low	1800 mm (1.8 m) spacing with fixing T; 1200 mm (1.2 m) spacing with fixing T; 900 mm spacing with fixing S
   Medium	1800 mm (1.8 m) spacing with fixing U; 1200 mm (1.2 m) spacing with fixing T; 900 mm spacing with fixing T
   High	1400 mm (1.4 m) spacing with fixing U; 1200 mm (1.2 m) spacing with fixing T; 900 mm spacing with fixing T
   Very high	1050 mm (1.05 m) spacing with fixing U; 900 mm spacing with fixing T
   Extra high	900 mm spacing with fixing U

3. 3

   Ceiling joists

   3 m at 600 mm spacing, any wind zone: 140 × 35, spanning up to 3.3 m; or 140 × 45, spanning up to 3.6 m

   Why Ceiling joists carry only the ceiling across the room, so their size follows their span and how far apart they are, the same in every wind zone.

   NZS 3604:2011 10.2.1.6, Table 10.3

4. 4

   Ceiling battens

   70 × 35 at 600 mm spacing, spanning up to 900 mm Ceiling: A lining lighter than 17.5 kg/m². Solid 70 × 45 dwangs at no more than 900 mm spacing between the chords, rafters or joists may carry it instead of battens.

   Why Battens carry the ceiling lining between the joists, truss chords or rafters they are fixed to, so their span decides their size; the heaviest ceiling they may carry is fixed.

   NZS 3604:2011 13.2, Table 13.1

5. 5

   Fixing types

   Type E: 2 skew nails, 90 × 3.15, and 2 wire dogs, or another holding at least 4.7 kN. Type S: 2 gun nails, 90 × 3.15, or another holding at least 0.8 kN. Type T: 1 self-drilling screw, 10g, 80 mm long, or another holding at least 2.4 kN. Type U: 1 self-drilling screw, 14g type 17, 100 mm long, or another holding at least 5.5 kN.

   Why The tables name each fixing by a letter; here is what each letter used above is made of and what it must hold.

   NZS 3604:2011 Tables 10.1, 10.2, 10.5, 10.7, 10.8, 10.10 to 10.12 and 10.15

Other members

Type a span for each member your roof has. A member left empty is skipped.