SCOPE AND GENERAL

GENERAL

Steel roof trusses are engineered and manufactured to an exacting standard which require special handling, erection and bracing techniques. To ensure that the expected performance is achieved, it is imperative that all relevant parties are familiar with the requirements set out in this document.

The guidelines in this document are a subset of the full Australian Standard® AS4440-2004 “Installation of Steel trusses”, and as such should be read in conjunction with this Standard.

IDomain acknowledges Standards Australia for permission to reproduce some of the drawings and technical content from within AS4440-2004.

APPLICATION

This document intends to apply to  Steel roof trusses within the following general limitations:

  • Residential structures (NCC Building classes 1, 2, 3 and 10) and light commercial structures.
  • Maximum roof pitch 45 degrees.
  • Maximum truss span 16 m.
  • Maximum design wind speed of 74 m/s.

DOCUMENTATION

It is the builder’s responsibility to supply all of the relevant information required for the truss designs. It is recommended that the truss manufacturer confirms all details prior to manufacture.

    • Layout

    A roof truss layout must be obtained prior to erection, with the following points considered:

    • Check dimensions of the supporting structure prior to manufacture.
    • Check the truss layout to identify the trusses, and also check for the correct orientation of trusses – two span, multiple and cantilever trusses.
    • Check that the supporting structure is adequate for the loads to be applied, especially where girder trusses are located, and lintels.
    • Check that information on roof bracing, bottom chord bracing (including the need for BC ties, if applicable) and any other applied loading (solar tank etc.) on the roof is provided.
    • Check that information on truss to truss connections, tie-downs, web-ties, scabs etc. is provided clearly on the layout.

    TYPICAL TRUSS LAYOUT AND TRUSS TYPES (Note: bracing not shown for clarity)


    Component to create gable-end verge.

    Creates roof plane by scotching over main trusses.

    Girder truss that supports hip-end trusses such as hips and, jacks trusses.

    Girder truss that creates dutch hip style roof by supporting hips and jacks trusses.

    Hip-end trusses that are supported by  truncated girder and creates a hip plane.

    Truss that supports creeper trusses and creates hip roof plane.

     Hip-end trusses that are supported   by hip truss and creates hip plane. 

    Truss that creates hip plane by truncating and allowing hip & jacks truss top chords to fly over.

    Truss that creates roof planes and does not support other trusses

    1.4.2 Hot Water Services

    Hot water services are best supported directly on internal walls, but where this is not possible, and the trusses are required to carry this load, then the truss manufacturer must be consulted for special design.

SERVICES

TRUSS TERMINOLOGY

1.4.3 Solar Hot Water Services

For solar powered hot water services, with internally or externally mounted water storage tanks, refer to the truss manufacturer for appropriate details. If the solar tank or panels are installed on the roof, seek advice from the truss manufacturer.

Solar hot water tank loads would be normally reflected on the truss layout.

If trusses require modification to accommodate these services, it is best practice to consult the truss manufacturer before any alterations are made to a truss.

Do not cut out any truss member without asking!

Installation Guidelines for Steel Roof Trusses (to be read in conjunction with AS4440-2004) September 2016

ANCILLARY Steel

Check that adequate ancillary Steel is available where required (eg, for temporary bracing).

  • TRANSPORT AND STORAGE

During transportation, in either flat or upright positions, the trusses must be fully supported, taking care whilst tying down to avoid putting undue strain on the truss members. Trusses should be stored on the job site clear of the ground and kept flat to avoid distortion. All trusses should be inspected on delivery, and any damaged trusses reported to the truss manufacturer immediately to ensure correct rectification.

It is best practice to install roof trusses within a week or two prior to installation of roof cladding.

SAFETY

The installation of Steel roof trusses must adhere to the relevant safety work practices for the general construction of roofs. This will require that barriers or safety lines be installed at the appropriate time. These systems must not modify the trusses, nor put loads onto the trusses, unless prior written approval is provided by the truss manufacturer.

 

Section 8.5 of the Safe Work Australia publication, “Preventing Falls in Housing Construction – Code of Practice – July 2012” provides guidance on safe erection methods for roof trusses. It is recommended that the requirements in this Code of Practice are well understood by the installer prior to erecting trusses.

 

Under the heading SAFE ERECTION METHODS FOR ROOF TRUSSES, this Safe Work Australia publication provides strict guidelines for a person erecting trusses. It states that at no time is any person to stand on or work from an external wall top plate without suitable fall protection. Below is an extract from this publication:

 

The erection of trusses may be undertaken from internal wall top plates or from scaffold planks supported on internal wall top plates provided:

 

  • No person works closer than 1.5 metres to an external wall, including gable end walls.
  • No person is exposed to the risk of a fall into a stairwell or other void.
  • Planks are adequately supported across their spans.

 

The allowable spans for Steel planks are given in Table

1 of section 2.2 Appendix B of “Preventing Falls in Housing Construction – Code of Practice – July 2012”. Laminated Steel, aluminium and steel planks must be used in accordance with the manufacturer’s directions.

 

When trusses are erected at up to 600 mm centres, persons working between the trusses to fix or brace them can use the erected trusses as a form of fall protection under controlled conditions as described below. If trusses are erected at greater than 600 mm centres, refer to Section 8.5 of this Code of Practice for suggested methods of working safely at heights.

 

Truss bottom chords are considered a safe working area for a competent person if all the conditions below are met. If the person erecting trusses is to walk or work from the bottom chords of the trusses, you should ensure that:

 

  • Trusses are adequately braced to stabilise the structure. If the bottom chord is used to support the person erecting trusses, then it should be laterally restrained by ties at a maximum 3000 mm centres (refer Section 3.6.2 for more details).
  • Only a competent person works at heights.
  • Suitable footwear that provides a good foothold is worn.
  • A nominated competent person from the truss erection team oversees the work.
  • A competent person or the truss manufacturer/supplier has provided the necessary detail and instructions, including advice in regard to installers standing on the bottom chord.
  • The bottom chord is visually checked by a nominated competent person for defects that may compromise the material’s structural integrity (ie, knots, splits, cracks and rotting Steel) before walking on it.

ROOF ANCHORS & GUARDRAILS

Roof trusses are not normally designed to resist loading from roof anchors or guardrails. Seek advice from the truss manufacturer. Safety anchor requirements (type and location) should be determined and given to the truss manufacturer before the detailed design of trusses occurs.

 

Read IDomain   Technical Update TU26 for further information on upgrading trusses to receive guardrail posts.

TRUSS MODIFICATION OR REPAIR

Trusses must not be modified on site without the prior written approval from the truss manufacturer.

 

The installer must report any damage, alterations or installation errors to the truss manufacturer immediately and must not attempt to repair a truss without a rectification detail from the truss manufacturer.

 

It must be noted that trusses and the type of damage could vary immensely, and each repair should be treated on its merits. The truss installer must refrain from using his prior knowledge or any ‘standard’ detail that he might have.

CONSTRUCTION LOADS

Extreme caution must be demonstrated when placing construction loads on roof trusses. Stack only a reasonable amount of materials, by ensuring they are located along external supports or directly over internal supports of a properly braced structure. Construction materials must not be placed at locations that will produce instability such as ends of cantilevers or girder to girder connections, and should not be dropped on trusses.

 

Failure to heed these recommendations could result in bodily injury and/or property damage.