Zinc Standing Seam Calculator — Sheets, Clips & Underlay

For double-lock standing seam, the common cover (tray) widths are 430mm, 530mm and 600mm — these are the finished seam centres, so you divide the roof width by them directly. Each tray is rolled from a wider flat coil: about 70mm of metal is consumed forming the double-lock seam, so a 430mm cover tray comes from roughly 500mm of coil and a 530mm cover tray from a 600mm coil (the international standard). 530mm cover is the most common.

Standing seam clips (fixed or sliding) sit at a maximum of 330mm centres in the field area, with at least 5 fixed clips per panel. For a 5m tray that is about 16 clips. Tighten the spacing to 200mm along roof edges and 150mm where two edges meet (corners) to resist wind uplift in those zones (VMZINC Standing Seam Installation Guide 2022).

A ventilated separation layer is required beneath zinc to allow drainage, airflow and free movement of the trays. Common purpose-made products are structured (3D) separation membranes such as Delta-VMZINC, Powerlon Metalix or Klober Permo Sec 400, which sit between the zinc and the deck. A traditional bituminous-felt-on-boarding build-up is also used. (Do not confuse these with PIR insulation boards like IKO Enertherm ALU, which are thermal insulation, not a separation layer.)

Zinc roofing typically lasts 80–100+ years. It develops a protective patina over time that self-heals minor scratches. It's one of the longest-lasting roofing materials available.

Double-lock standing seam is weathertight down to about 7° unsealed. Below that — down to 3° — the seams must be sealed with closed-cell expanding strips, and adequate clip density is essential. So 3° is achievable as a sealed, low-pitch detail, but treat 7° as the safe unsealed minimum (SIG Zinc & Copper / elZinc).