Galvanized vs Galvalume - What’s the Best Metal for Siding and Roofing?

When it comes to the various types of metal siding and roofing for a builder or homeowner to select from, there are two options: Galvanized and Galvalume.

The oldest type is galvanized metal. This is a sheet of steel which has been coated with a thin layer of zinc oxide. The zinc is applied to the steel to protect it from the atmospheric elements which can lead to corrosion and rust. Galvanized metal can begin to corrode within 10 to 15 years depending on the atmospheric elements the metal faces. The slowly occurring corrosion and rust will eventually weaken the galvanized metal and lead to a complete breakdown of the steel.

Besides siding and roofing, many manufactured other items of steel are galvanized for protection. Some examples include city street/park furniture, building frameworks, balconies, verandahs, staircases, ladders and walkways.

Galvalume is the trade name for a newer patented sheet steel product. Items created from Galvalume steel coils are made with steel panels having a coating of corrosion resistant aluminum-zinc alloy applied by a continuous hot dip process. The nominal composition of the coating is 55% aluminum, 43.5% zinc and 1.5% silicon. The alloy coating of aluminum and zinc combines the best properties of both metals. It has the corrosion resistance and heat reflectivity characteristic of aluminum coatings, with the formability and galvanic protection of cut edges characteristic of zinc coatings. The silicon is included in the coating alloy, not to enhance the corrosion performance, but to provide good coating adhesion to the steel substrate when the product is roll-formed, drawn, or bent during fabrication.

Galvalume is an excellent product for long-life roofing and siding material. The aluminum additive, along with the zinc, allows small particle areas to form within this coating. Any corrosion that occurs does so within these open particle areas. Galvanized metal corrodes in a linear fashion and eventually depletes the zinc coating entirely. Galvalume, on the other hand experiences some corrosion, but on a smaller and less significant scale. Galvalume will not breakdown completely, as galvanized will.

Based on 30-year atmospheric corrosion R&D tests, Galvalume steel is projected to outlast galvanized steel in various atmospheres by up to nine times. Galvalume sheet has also exhibited excellent corrosion resistance in a variety of accelerated tests and atmospheric exposures and on buildings. It has demonstrated equal or better performance than prepainted G90 galvanized in corrosion at flat areas, paint damaged areas, formed areas and roof drip edges.

Galvalume is a trademark of BIEC International Inc.

SOURCE: http://www.weatheredgebc.com/galvanized-vs-galvalume.php