A superior long-life roof system calls not only for the right material, but for the application of good design, installation and maintenance practices. The survey confirms the strong performance of unpainted 55% Al-Zn, whilst at the same time emphasising that successful performance relies on "best practice" throughout the project.
For example, areas around various types of roof-mounted equipment and stacks are often dirty and rust-stained; good maintenance and the use of corrosion-resistant materials to support roof-mounted equipment would minimise this.

The survey revealed combinations of galvanised steel, 55% Al-Zn, aluminium, painted galvanised and lead being used for curbs, flashings and roof ancillaries. Designers and installers should be careful to select only those materials that are the most compatible with 55% Al-Zn, and should be discouraged from using short-life galvanised steel parts on a long-life 55% Al-Zn roof system.

If corrosive vapour is being discharged from a roof stack, it may be necessary to post-apply protective coatings to the roof panels in the adjacent affected area.

Age: 18 years
Slope: 14 degrees
Environment: Urban
Location: Falun, Sweden

Careless routine maintenance. Here a storm filter was plugged by debris, due to lack of regular maintenance. Ponding resulted, and corrosive agents released by the bitumen used to seal roof laps had caused red rust. A neutral cure sealant should have been used.

Age: 24 years
Slope: < 5 degrees
Environment: Rural
Location: Münster, Germany

Age: 21 years
Slope: 6 degrees
Environment: Urban
Location: Falun, Sweden

Poor installation practice. In the top picture, damage to the seams during installation resulted in accelerated corrosion. On the bottom, iron debris left on the roof has caused red rust, though fastener and sheet are both in good condition. Good installation practice and post-installation clean-up would have avoided this. Although there is no accelerated corrosion in this case, the rust stain creates an undesirable appearance and may lead the building owner to think his roof is failing.

Age: 21 years
Slope: < 5 degrees
Environment: Urban
Location: Münster, Germany

Poor installation and maintenance practice. How not to do it. The top picture shows how the careless use of asphalt as a patch has accelerated corrosion near the drip edge of the roof. In the bottom picture, a spare bit of metal flashing was left lying on the surface of the 55% Al-Zn roof, trapping moisture and debris and leading to accelerated corrosion.

Age: 17 years
Slope: 33 degrees
Environment: Urban/light marine
Location: Stockholm, Sweden

Incompatibility. Galvanised panels should not have been used here; water flowing from the 55% Al-Zn panels on to bare galvanised steel causes accelerated corrosion through "inert catchment".

Poor material choice for ancillary items. Some washers on this 17-year-old roof have rusted, and will eventually fail. The bottom picture shows that properly selected washers on the same roof have performed well.

Age: 20 years
Slope: 5 degrees
Environment: Urban/light marine
Location: Tyresö, Sweden

Age: 10 years
Slope: 10 degrees
Environment: Urban
Location: Le Thillot, France

Poor material choice for adjacent chimneys. In the top picture, the use of Cor-Ten steel for the chimney in the background has caused minor pitting corrosion to the 55% Al-Zn roof after 20 years; copper ions from the chimney material, swept down by rain, will continue to attack and damage the roof. On the bottom, the Cor-Ten chimneys have caused some corrosion, but there is so far no perforation of the coating. These problems could have been avoided if the recommended design parameters had been observed.