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Roof framing: prefabricated trusses

How to install prefabricated nail-plated timber roof trusses in Australia: AS 4440, AS 1720.5, hip vs gable layouts, temporary bracing, hold-down, tolerances.

By Dan Waring. Last updated 10 May 2026. Verified 10 May 2026.

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TL;DR

Prefabricated nail-plated timber roof trusses are engineered off-site, delivered as a complete set, and lifted onto wall plates in one sequence. Standards: AS 4440:2004 (installation) and AS 1720.5:2015 Amd 1:2019 (design), both under NCC 2022 H1D6. Supply-and-set on a 200 m2 footprint runs $9,000 to $15,000 in 2026. The most common defect is inadequate temporary bracing: unbraced trusses have collapsed before battens were fixed. The second is skipped or wrong hold-down connectors at the wall plate, the leading cause of roof loss in storm events.

When you do this

After wall frames are completed, inspected, and tied down. Sequence: truss delivery, lift-and-set, temporary bracing, permanent bracing, battens, roofing. Trusses are on the critical path.

Who’s involved

RoleResponsibility
Truss manufacturerDesign drawings, engineering certificate, supply
ChippyLift-and-set, bracing, hold-down connections
BuilderConfirm drawings match structural plans before ordering
Structural engineerWind classification, tie-down schedule, site approvals
Crane / hiab operatorLift and set (HRCW: SWMS required)
RooferBattens and roofing after trusses are braced

Steps

1. Confirm drawings and engineering certificate before ordering

Every set must come with a layout drawing (truss positions, types, spacings, bearings) and an engineering certificate to AS 1720.5:2015 Amd 1:2019 for the site wind classification. Check the layout against the structural engineer’s framing plan before ordering. Changes after order require re-engineering.

Source: AS 1720.5:2015 Amd 1:2019, Standards Australia (verified 2026-05-10); NCC 2022 H1D6, ABCB (verified 2026-05-10).

2. Inspect on delivery

Per AS 4440:2004, inspect each truss before installation: confirm type matches the layout drawing, connector plates are fully seated, and no members are cut, drilled, or damaged. A damaged truss needs written engineer rectification before use. If storing before installation: flat on packers, covered but ventilated.

Source: AS 4440:2004, Standards Australia (verified 2026-05-10).

3. Key truss types

Components: top chord (sloped members, carry battens), bottom chord (horizontal, acts as ceiling joist), web members (internal diagonals/verticals), connector plate or nail plate (toothed steel plate at every node).

Hip roof truss types (gable roofs use common trusses only):

TypeRole
Common (standard)Full-width; the majority in any roof
Girder (truncated girder)Load-critical at the hip end; carries jack and creeper loads
Hip trussForms the hip line; extended top chord from girder to apex
Jack / creeperShorter fill trusses at the hip end

The girder carries concentrated loads from every jack and creeper; install and brace it before any other hip-end truss.

Source: RMIT Learning Lab, Trusses for hip roof systems (verified 2026-05-10).

4. SWMS and fall protection before lifting

Truss installation is HRCW (fall risk greater than 2 m). A site-specific SWMS covering fall protection, lift plan, and bracing procedure is required before work begins.

Source: WorkSafe Victoria, Safe erection of roof trusses checklist (verified 2026-05-10).

5. Mark plates, set girder first (hip roofs), then set common trusses

Mark every truss position on both wall plates before lifting. On a hip roof, the truncated girder at the hip end must go first: set, confirm plumb, and brace diagonally back to the building corner before releasing the crane. A misaligned girder requires pulling the hip end apart to correct.

Set common trusses from one end to the other. Lower onto both bearing points, confirm seating, fix a spacer at the specified spacing (typically 600, 900, or 1,200 mm), then install temporary bracing before moving to the next truss. Do not leave more than 3 to 4 trusses unbraced at any point.

Temporary bracing must remain until permanent bracing and battens are complete. Per AS 4440:2004, the minimum temporary brace at less than 900 mm spacing is 50 x 25 F5 or MGP10 boards at max 3,000 mm along top chord panel points.

Source: AS 4440:2004, Standards Australia (verified 2026-05-10).

6. Fix hold-down connections to wall plates

Every bearing point needs the hold-down specified in the structural drawings. Type is driven by wind classification:

ConnectionTypical application
Skew nails (2/3.05 mm dia)N1-N2
Truss clips or framing anchors (MiTek or Pryda)N2-N3
Hurricane straps (over top chord, both sides of plate)N3-N4 and all cyclonic
Engineered hold-down (bolt-through)Cyclonic C1-C4

In cyclonic regions (AS 4055:2021 Regions C and D), do not apply non-cyclonic fixings. One missing connector is the link that fails in a wind event.

Source: NCC 2022 H1D6, ABCB (verified 2026-05-10); AS 1684.2:2021, Standards Australia (verified 2026-05-10).

7. Install permanent bracing, then battens

Three elements per AS 4440:2004: (1) top chord diagonal steel brace (Pryda Steelbrace or equivalent) from ridge to eaves; (2) bottom chord bracing and web ties; (3) the full batten layer, which provides permanent lateral restraint to all top chords. Fix battens to every ply of multi-ply trusses per the supplier’s schedule and AS 1684. Only remove temporary bracing after all three elements are complete.

Source: AS 4440:2004, Standards Australia (verified 2026-05-10).

8. Openings and the no-modification rule

For skylights, hatches, or penetrations: trusses each side are doubled or tripled as trimmers, with a header between them. Design comes from the fabricator’s engineer. Never cut, notch, drill, or modify any truss member without written engineer approval; on-site modifications transfer structural liability to whoever made the cut.

Tolerances and acceptance

ElementStandardRequirement
Truss plumb (erection)AS 4440:2004Height/50 or 50 mm max out of plumb, whichever is less
Truss bow (erection)AS 4440:2004Bowed-length/200 or 50 mm max, whichever is less
Truss plumb (finished workmanship)HIA GuidePending HIA member access. [HIA-082]
Bottom chord deflection under loadHIA GuidePending HIA member access. [HIA-083]
Truss spacing (deviation from specified)HIA GuidePending HIA member access. [HIA-084]
Minimum bearing on wall plateAS 4440:2004 / manufacturerPer manufacturer’s layout drawing and AS 4440 Section 2
Hold-down connectorAS 1684.2 / structural drawingsPer structural engineer’s tie-down schedule for the wind classification

Documents needed

  • Manufacturer’s layout drawing and engineering certificate
  • Structural engineer’s framing plan and tie-down schedule
  • Site wind classification (AS 4055:2021 Amd 1:2024)
  • SWMS for truss installation (HRCW)
  • Crane or hiab pre-start and lift plan

Common holds

  • Trusses ordered before drawings confirmed. Changes after order require re-engineering.
  • Wrong hold-down connectors. Skew nails alone are not sufficient in N3-N4 or cyclonic zones. Check the tie-down schedule at every bearing before battens start.
  • Temporary bracing removed too early. A few batten rows is not a substitute for continuous permanent bracing.
  • On-site modification. Cutting or removing a connector plate without engineer approval is a structural defect that cannot be fixed by re-nailing.
  • Girder misaligned at hip end. Correcting it after jack and creeper trusses are set requires pulling most of the hip end apart.
  • Wrong truss in wrong position. Check every truss against the layout drawing before setting.

References

See also

Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.

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