Profiled metal roofing – insufficient cover at sheet laps
Causes
Listed under: metal, Roof, cladding, roof cladding, profiled metal
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