Lintel Sizes: reading it right off NZS 3604

How to size a lintel over an opening using NZS 3604:2011, and when the prescriptive tables run out.

A lintel is the member that spans over a window or door and carries the load above it. Get the size right and the load path stays sound — get it wrong and you’re back on site pulling out a wall. This page explains how the NZS 3604 lintel tables work and where they stop applying.

How to size a lintel

Read the required lintel size off NZS 3604:2011 Tables 8.10 / 8.11 in your licensed copy of the standard — we don’t reproduce those sizes here. You select against four things:

Opening width — wider openings need a bigger lintel.
Roof load — light (steel) versus heavy (tile). Heavy roofs push the size up.
Wind zone — higher wind means bigger uplift forces.
Single vs double-storey — an upper-storey lintel carries less than a ground-storey lintel under a 2-storey load.

Wide openings and heavy (tile) roofs usually push you into doubled members or LVL. Always verify against the standard for the actual load case.

How the load path works

A lintel transfers the load above an opening down through the trimmer studs to the foundation. Both the studs supporting it and the studs tying it in matter:

Trimmer studs (jamb studs) — the lintel sits on these at each end. The number of trimmers and king studs required increases with the opening width; check NZS 3604:2011 §8.6.
King studs — full-height studs outside the trimmers that tie the assembly into the top plate.

When to skip the prescriptive path

The NZS 3604 lintel tables only cover prescriptive scenarios. Get an engineer’s PS1 when any of these apply:

Openings over 3m.
2-storey lower-floor lintels.
Point loads from beams.
Any other non-standard load case.

Reference: NZS 3604:2011 §8.6 plus Tables 8.10 / 8.11.

Plain-English guide, not advice. This page helps you understand and navigate the rules — it is general information, not design, engineering or consent advice, and it does not reproduce the copyrighted tables of NZS 3604 or any Standard. Always check the current Standard or Acceptable Solution and your BCA, and use a suitably qualified LBP, engineer or QS where it matters.

Do it in Toolie

Put this into practice with the NZS 3604 take-off · the lintel/beam span calculator · the rafter span calculator. Try Toolie free — no signup — or open this topic in the Toolie app.

Common questions

Which NZS 3604 tables give lintel sizes?

Lintel sizes come off NZS 3604:2011 Tables 8.10 and 8.11, read in your licensed copy of the standard. You select against opening width, roof weight (light vs heavy), storeys and wind zone.

What determines the lintel size I need?

Four things: opening width (wider needs a bigger lintel), roof load (light steel vs heavy tile), wind zone (higher wind means bigger uplift forces), and single vs double-storey (an upper-storey lintel carries less than a ground-storey one under a 2-storey load).

What are trimmer studs and king studs?

Trimmer (jamb) studs are what the lintel sits on at each end, carrying the load down to the foundation. King studs are the full-height studs outside the trimmers that tie the assembly into the top plate. The number of trimmers and king studs required increases with opening width — check NZS 3604:2011 §8.6.

When do I need an engineer's PS1 instead of the tables?

For openings over 3m, 2-storey lower-floor lintels, point loads from beams, or any non-standard load case. The NZS 3604 lintel tables only cover prescriptive scenarios.

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