Metal Roofing: What’s The Difference Between Galvanised and Galvalume Steel?

By November 27, 2019Metal Roofing

As metal roofing Auckland has become one of the most popular roofing materials to choose from, there are now various types and treatments available as well. Steel, in particular, is affordable and longlasting – provided you protect it against rust. If you’re installing metal roofing on your Auckland home, here are the differences between galvalume and galvanised steel. 

Why Is Rust A Problem?

When you install metal roofing on your home, your first thought should be all about preventing rust from accumulating. As an alloy that contains iron, steel is bound to start rusting, after prolonged exposure to moisture and oxygen. As soon as the rust starts appearing, your roof becomes weakened and unattractive. To avoid it, you need an anti-rust coating for your roof.

Galvanised VS Galvalume Coatings 

Galvalume and galvanised steel are two of the most popular rust-resistant coatings you can find. Galvanised steel is a metal roofing material which has been manufactured with a coating of zinc within its makeup. The zinc inhibits the growth of rust, which is why it’s used as an anti-rust coating. Galvalume is also steel sheeting, made with a coating of a combination of both zinc, silicon and aluminium. It creates an anti-rust barrier, which protects the steel from oxidising. 

Both products are effective in preventing the formation of rust on a metal roof – however, which one is used on your own roof is mostly dependent on your roofing contractor’s and your own personal preference, because the difference in price between the two is minimal. 

Do They Last Long?

Between 5 – 10 years, galvalume roofing could show a little bit of corrosion, particularly around the holes that were drilled to fasten the sheeting to the roof. The galvanised sheeting will look brand new, except for where it has been attached to the roof for the same reason.

Between 10 – 15 years, the galvanised steel will start showing some age, with corrosion spreading from the starting point where it was punched and attached to the roof. The galvalume will have a few isolated spots of corrosion. 

At 20 years, the age and wear on galvalume sheets are mostly unnoticeable, but it might have discoloured slightly due to its aluminium content. The galvanised steel might show a slightly rusty colour, depending on the climate of the area. 

Unpainted galvanised steel typically lasts between 10 and 15 years, depending on the climate of the area. For example, it would last fewer years than that if the building was in a coastal town. The salty sea air would affect the galvanised steel at a faster rate. Galvalume can last up to 40 years, even unpainted; however, both types of anti-corrosion metal roofing can be painted for an added layer of protection. 

As mentioned before, whether you choose galvanised or galvalume steel for the metal roofing on your Auckland home is a personal preference. But, whichever option you select will need to be maintained regularly, which can be costly. Remember to ask your roofing company for advice, so that your metal roof stays rust free for the duration of its intended lifespan. 


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