Main features

  • Proven, versatile system for roofing flat, curved and ‘free-form’ roofs.
  • Weather-tight down to 7º of pitch, 3º if seams are sealed..
  • Discrete joints give a light, elegant appearance.
  • Modern profiling and seaming machines facilitate short installation times.
  • On-the-roof detailing uses folding techniques or soldered joints – no mastic!
  • Items such as snow guards and life line attachments are readily available.

Basic system information

  1. elZinc® Standing seam roofing tray, nominal max. length 10m.
  2. Standing seam joint (normally follow line of maximum pitch)
  3. Undercloak
  4. Overcloak
  5. Welt of standing seam
  6. Expansion gap at seam base
  7. Seam centres dimension. Normally from 430 to 600mm
  8. Stainless steel ‘fixed’ clip – anchors the tray in position
  9. Stainless steel ‘sliding’ clip – allows longitudinal expansion
  10. Self-expanding sealing strip for roofs pitched under 7º

The standing seam joint

The joint requires 70mm of material to make.  It is formed by seaming together profiled trays of zinc as illustrated below.

Cross joints

Transverse joints vary according to roof pitch.  They are needed to introduce expansion joints on large roofs or around details.


  • Pitch:       3º and above
  • Height:    60mm

Often used as an expansion joint on long, low pitched roofs.  The step in the substrate can be formed using a fillet

  1. Lower roofing tray
  2. Continuous fixing strip
  3. ‘T’ plate with folded back edge
  4. Upper roofing tray
  5. Expansion/contraction gap

Double lock cross welt.

  • Pitch:       7º and above
  • Width:     Approx. 20mm

The preformed ‘slide in’ type (shown here) allows for perfect rainwater drainage.

Does not function as an expansion joint.

  1. Lower roofing tray
  2. Upper tray

Lap lock.

  • Pitch:       10º and above
  • Lap:         Approx. 180mm

Often used as an expansion joint on long roofs.

  1. Lower roofing tray
  2. Soldered continuous cleat
  3. Upper tray
  4. Expansion/contraction gap

Single lock cross welt.

  • Pitch:       25º and above
  • Width:     40mm fold on lower tray, 30mm on upper tray.  Can be used as an expansion joint on long roofs.
  1. Lower roofing tray
  2. 40mm fold
  3. Upper tray
  4. Expansion/contraction gap


The system is installed across the roof in either direction, or preferably outwards from a centrally placed undercloak – undercloak tray that ensures trays of equal width (and therefore symmetry) at both ends of the roof.

Dimensioning and fixing

If the length of the roofing trays is over 1,5m the clips used to secure them to the substrate must allow the zinc to expand and contract, and these trays use a combination of fixed clips and sliding clips to accomplish this.

The position of the fixed clip zone depends on roof pitch – to avoid the trays from buckling, the steeper the pitch, the higher the anchoring band of fixed clips is positioned.  The thermal movement generated in the trays is accommodated by a gap introduced in the detail at the foot and at the head of the trays.

The standing seam, angle seam and flat lock panel systems all use the same set of seam centres, which are tied into commercially available coil widths.  Therefore, the following table can be used to determine the bay widths, thicknesses, and also to specify the number of fixings per m2 for each of these systems.


System dimensioning Fixing requirements – Number of clips per m2/clip centres in cms related to building height
<8m 8m < H <= 20m 20 a 100m
Thick Bay width Centre Edge Corner Centre Edge Corner Centre Edge Corner
0.7 430 3.9/48 3.9/48 6.4/29 3.9/48 5.5/34 9.6/20 3.9/48 7.7/25 12.8/15
0.7 530 3.9/48 3.9/48 6.4/29 3.9/48 5.5/34 9.6/20 3.9/48 7.7/25 12.8/15
0.7 600 3.9/43 3.9/43 6.4/26 3.9/43 5.5/30 9.6/17 3.9/43 8.5/20 12.8/13
0.7 630 4/40 4/40 6.4/25 4/40 5.4/29 10/16      

Notes:  Assumes a nominal clip pull out load of 560N. Valid for non-exposed locations.

Various factors affect wind uplift – (location, exposure, orientation and roof geometry) and advice should be sought from elZinc® when determining tray widths for projects in exposed locations.  This is not only to ensure that the cladding does not suffer during storms, it is also to avoid fluttering of the trays during periods of continuously windy weather.

Bay widths may be narrowed to the next standard width in order to reduce quilting in the sheets if a flatter appearance to the cladding is required, especially for wall cladding or steeply pitched roofs.



Double lock standing seam | Download

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