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Expansion Joint Detail
last updated 25/07/16

COLORBOND® and ZINCALUME® steel roofing expands and contracts with changes in temperature.
This article features a standard expansion joint which is common place on projects with long runs of roof sheeting. Sometimes these joints are referred to as 'step joins'. In addition to allowing for expansion, it provides an effective solution for end lapping sheeting where the sheet length is longer than the maximum transportable sheet length.

Please read the disclaimer relating to this article.

Expansion and Contraction of COLORBOND® and ZINCALUME® steel (Based on figures from SAA HB39 - 1997)
Sheet Length (mm) 10°C change (mm) 50°C change (mm) 75°C change (mm)
5000 0.6 2.9 4.3
10000 1.2 5.7 8.6
15000 1.8 8.6 12.8
20000 2.3 11.4 17.1
25000 2.9 14.3 21.4
30000 3.5 17.1 25.7

click to enlarge

Typical expansion joint

(this picture is extracted from Stramit Building Products' content residing on the SteelSelect site)

Note: The movement (change) is from the centre of the sheet towards each end. Each end has half the expansion/contraction shown in the table above. Other factors should be considered, including flexing of the purlins and expansion and contraction of the building frame. There is no need to allow for expansion and contraction across the width of the sheeting because the profile of the ribs absorbs the movement.

As a guide, temperature change for light colours is 50° and for darker colours is 75°. Architects and designers should consider the temperature changes for their specific project and seek specialist advice in severe conditions.

An expansion joint's prime role is to reduce the stresses on fastener connections.
Fasteners have been known to fail when expansion and contraction of pierce -fixed roofing has not been considered in the roof design.
Typically, light colour pierce-fix roof sheeting should have a maximum sheet length of 25 metres, dark colour pierce-fix roof sheeting has a maximum sheet length of 17 metres (As published by Stramit Building Products' Roofing & Wall Flashing Architectural detailing brochure reference pg:10).

Additional SteelSelect site resources
Corrosion Technical Bulletin CTB 8 - Building Applications
Material selection, Design, Unwashed Areas, End lapping and slip sheets, Pitch transition flashing, Low pitched roofing, Expansion joints.
Expansion - Using LYSAGHT® Roofing and Walling Section 10.5
Extract from the Using LYSAGHT® Roofing and Walling brochure.
Design Topics to consider
Maximum roof lengths for drainage - Using LYSAGHT® Roofing and Walling Table 2.4.1
Extract from the Using LYSAGHT® Roofing and Walling brochure; Table 2.4.1 Maximum roof lengths for drainage measured from ridge to gutter, includes calculation for allowing for penetrations.
Stramit Roof Slope
Roof slope factors including economy, drainage, durability, wind resistance, safety, services and aesthetics.
Material Selection
  • Material Choices
  • Matching material grade to the project conditions
  • Compatibility of Direct Contact between Metals or Alloys
  • Acceptability of Drainage from an upper surface to a lower metal surface
  • Classification of COLORBOND® steel colours for BCA and NSW BASIX
    Expansion Joint Detail (Baffle Flashing)
    Download CAD versions of this flashing
    Typical sizes for a baffle flashing
    • A = 250mm

    click to enlarge

    click to enlarge

    Download CAD versions of this detail
    Download PDF versions of this detail

    Detail Comments
    A step is created by having the purlin slightly higher on the up side of the roof. The height difference of the purlins should be 15mm plus the height of the roofing profile.
    The minimum overlap of the upper sheeting is 250mm and the gap between the end of the lower roof and the top purlin should be a minimum of 25mm. The 'baffle flashing' is installed on top of the lower roof and the break is notched to suit the roofing profile.

    The expansion joint detail is common on many commercial roofing projects. Whilst this article refers to pierce-fix roofing sheeting, I should mention that some concealed-fix sheeting allows for expansion and contraction along the fixing clips, eliminating the need for an expansion joint detail. Generally speaking, when designing for this application you still need to consider the expansion and contraction for the overall sheet length and the flashings, consideration should also be given to the drainage capacity of the roof sheet.
    The download provided can be imported into your CAD drawing, saving you time and making your plans more precise. I welcome any comments or suggestions you may have on these details - contact form.

    Resource Acknowledgements
    Source: SteelSelect - author Richard Michael

    Publication Details: November 05

    Authors Disclaimers:  The information and advice contained in this article is of a general nature only, and has not been prepared with your specific needs in mind. You should always obtain specialist advice to ensure that the materials, approach and techniques referred to in this article meet your specific requirements. SteelSelect makes no warranty as to the accuracy, completeness or reliability of any estimates, opinions or other information contained in this article, and to the maximum extent permitted by law, SteelSelect disclaims all liability and responsibility for any loss or damage, direct or indirect, which may be suffered by any person acting in reliance on anything contained in or omitted from this document.