Profiled metal roofing – insufficient cover at sheet laps

Cause

Poor installation

Repair

  • if the roofing was installed in recent years, call the original installer back to make repairs – poor installation may lead to weathertightness problems or impact roofing durability
  • if the installer is no longer available, ask the supplier or manufacturer of the roofing material (if known) for advice. Many publish installation guidance on their websites
  • the Acceptable Solution E2/AS1 covers this area. The requirements for profiled metal roof cladding are found in section 8.4 of E2/AS1. Figure 39 has a drawing of the correct way to lap corrugated profiled metal roofing. It shows a side lap over an adjoining sheet being made over a full crest
  • extending laps for greater than this distance is not recommended. The NZ Metal Roofing Manufacturers’ Installation Guide for Metal Longrun Roofing and Cladding (version 1.0 May 2022) says: “Sheets should not be laid with a double lap, as this can cause accelerated corrosion in the lap area”
  • the Guide also says: “side laps should be fitted evenly and snugly without excessive gaps or tension”
  • profiled metal roofing manufacturers say end laps in profiled metal roofing should be avoided where possible, but where unavoidable should be sealed with a double bead of sealant
  • while sunscreen gives important protection while working on a roof, do not use sunscreen containing titanium dioxide or zinc oxide. These substances can cause irreparable damage to some factory finished roofing surfaces
  • always tell someone else when you plan to work on a roof and take the appropriate safety precautions. You can find details here