Openings and lintels to NZS 3604
Your opening, and what NZS 3604 asks of it from seven places at once: the lintel, its ends, holding it down, the trimming studs and the trimmers.
- NZS 3604:2011
Lintel
190 × 70
- Spans 2.4 m
- Uplift fixings at each end
- Trimming studs 70 mm thick
- Trimmers 45 mm thick
How it is worked out
Which table
Table 8.9, for a lintel holding up a roof only
Why What the lintel holds up chooses the table, and the roof's and wall's weights its columns and rows.
NZS 3604:2011 8.6.1, Table 8.9
Its loaded dimension
3 m, read on the table's 3 m row
Why The loaded dimension is the width of roof or floor the lintel carries. Between two rows the next one up is read, never a figure in between.
NZS 3604:2011 1.3, Table 8.9
The lintel
190 × 70, the first size in the table's order reaching 2.4 m; it spans 2.4 m; 140 × 90 reaches only 1.9 m
Why The table lists its sizes smallest first, so the first that reaches the opening's width is the one to use.
NZS 3604:2011 Table 8.9
Longest span of each size, loaded dimension 3 m, Table 8.9 Lintel, depth × thickness Longest span 90 × 70 1.1 m 90 × 90 1.2 m 140 × 70 1.7 m 140 × 90 1.9 m 190 × 70 2.4 m 190 × 90 2.6 m 240 × 70 3 m 240 × 90 3.3 m 290 × 70 3.7 m 290 × 90 3.9 m Its ends
On a 35 mm doubling or jack stud each end
Why The deeper the lintel, the more it carries to each end, so its depth decides whether a check in the trimming stud is enough or a doubling stud is needed.
NZS 3604:2011 8.6.1.5, 8.6.1.6
Holding it down
Uplift fixings each end, for a lintel up to 4.3 m: tied to the trimming stud and that to the floor framing, or 7.5 kN along the stud
Why Wind lifts the roof, and the lintel under it with it; where nails alone will not hold it, it is tied down at each end.
NZS 3604:2011 8.6.1.7, 8.6.1.8, Table 8.14
Trimming studs
70 mm thick each side
Why The studs each side of the opening carry the lintel's ends and the wall around the opening, so they thicken as it widens.
NZS 3604:2011 8.5.2, Table 8.5
Sill and head trimmers
45 mm thick, as wide as the studs
Why The trimmers frame the top and bottom of the opening, spanning its width between the trimming studs.
NZS 3604:2011 8.6.2, Table 8.15
Nails
4 of 75 × 3.15 skewed, or 2 of 100 × 3.75 end nailed; power-driven, 3 of 90 × 3.15 end nailed
Why The nails tie the lintel to its trimming studs, so the frame around the opening works as one.
NZS 3604:2011 Table 8.19
- The loaded dimension is the width of roof or floor the lintel holds up: half of each span bearing on it, eaves left out. Under a roof and wall, read the wall's at roof level; with a floor as well, the greater of that and the floor's. NZS 3604:2011 1.3, Figure 1.3, Tables 8.10 and 8.11 notes
- The lintel tables are for roofs up to 45°; a steeper roof scales its loaded dimension up first. NZS 3604:2011 8.6.1.3, Table 8.7
- A lintel may be two or more members side by side, each its full length, nailed together. NZS 3604:2011 8.6.1.5, 2.4.4.7