Metal roof

Zinc, standing-seam roof in Poland

Flat seam metal roofing was used here on the problem areas. Cauterets, France.

A metal roof is a roofing system made from metal piece, or tiles. It is a component of the building envelope.

Metal roofs protect buildings.

In the United States, metal comprises 10% of the overall residential re-roofing market.

History

Copper has played a significant role in architecture for thousands of years (see: Copper in architecture). In the 3rd Century B.C., copper roof shingles were installed atop of the Loha Maha Paya Temple in Sri Lanka.^[1] And the Romans used copper as roof covering for the Pantheon in 27 B.C.^[2] Centuries later, copper and its alloys were integral in European medieval architecture. The copper roof of St. Mary's Cathedral, Hildesheim, installed in 1280 A.D., survives to this day.^[3] And the roof at Kronborg, one of northern Europe's most important Renaissance castles (immortalized as Elsinore Castle in Shakespeare’s Hamlet) was installed in the 1585 A.D.^[4] The copper on the tower was renovated in 2009.^[5]

Earlier metal roofing was a sheeting in the form of corrugated galvanized steel and still find applications today in parts of the developing world. In addition, colour-coated steel roofs are popular in some of the Nordic countries such as Finland and Sweden.

Advantages

• Very durable in cold weather
• High percentage of recycled material and are 100% recyclable^[6]

Disadvantages

• Rusting (require maintenance to prevent corrosion)
• Copper and lead roofs can be targeted by metal thieves
• High heat conductivity of metals (particularly copper and aluminum) requires careful incorporation of insulation into the roof structure
• Cellular and radio reception may be negatively impacted

Misconceptions

It has been proven that metal roofs do not increase lightning strikes. But if lightning were to ever strike a person's roof, the metal disperses the electricity throughout the structure safely. In fact, it would be safer for a metal roof to be struck by lightning because it’s not flammable or combustible, lowering the risk of a fire.

Applications

Metal roofing can be used for residential and commercial buildings. The same material used for metal roofs can be used for siding as well. Metal roofing can also be applied over an existing roof.

Material types

• Corrugated galvanized steel. This describes the original product that was wrought iron–steel sheet coated with zinc and then roll formed into corrugated sheets. This product is still used today in most areas. The newer push of modern architecture and "green" products has brought these products back to the foreground.
• A blend of zinc, aluminium, and silicon-coated steel, sold under various trade names like "Zincalume", "galvalume", etc. Sometimes left in the raw zinc finish, but more widely used as a base metal under factory-coated colors.
• Standing Seam Metal. This is a metal product that comes in rolled form and in various widths. The material is "seamed" together using a special seaming tool that is run vertically up the panel to seal the joints and prevent water intrusion.^[7]
• Metal tile sheets. These are usually painted or stone-coated steel.
• Stainless steel. Available for harsh conditions and/or as a distinctive design element. Usually roll-formed into standing seam profiles; however, shingles are available.
• Copper (for main article, see: Copper in architecture). Copper roofs offer corrosion resistance, durability, long life, low maintenance, radio frequency shielding, lightning protection, and sustainability benefits. Copper roofs are often one of the most architecturally distinguishable features of prominent buildings, including churches, government buildings, and universities.^[8] Today, copper is used in roofing systems, flashings and copings, rain gutters and downspouts, domes, spires, vaults, and various other architectural design elements. At the Lyle Center for Regenerative Studies copper is used for regenerative principles of sustainable design: if the building were to be dismantled the copper could be reused because of its high value in recycling and its variety of potential uses. A vented copper roof assembly at Oak Ridge National Laboratories (U.S.) substantially reduced heat gain versus stone-coated steel shingle (SR246E90) or asphalt shingle (SR093E89), resulting in lower energy costs.^[9]
• Aluminum. One of the longest-lasting metals, but somewhat expensive compared to steel products. Aluminum roofs are very lightweight, corrosion-resistant, have high natural reflectivity and even higher natural emissivity, increasing a building's energy efficiency. Aluminum products with Kynar paints easily last over 50 years. The newest innovation is anodizing of the aluminum coil stock for use in architectural details and standing seam panels. The anodized layer is intimately bonded to the metal and is not normally subject to weathering and wear.
• Stone coated steel. Panels made from zinc/aluminium-coated steel with acrylic gel coating. The stones are usually a natural product with a colored ceramic coating.
• Lead is often used for church roofs and porches.
• Tin

Coating

Several different types of coatings are used on metal panels: anti-rust, waterproofing, heat reflective. They are made of various materials such as epoxy and ceramic.

Untreated Metal roofs absorb and retain heat which causes high building envelope heat loads.

Ceramic coatings can be applied on metal roof materials to add heat reflective characteristic. Most ceramic coatings are made from regular paint, with ceramic beads mixed in as an additive. Although an average ceramic coated roof material reflects 75% to 85% of solar radiations, performance drops by over 30% after a few years due to dirt build-up. Their composition and thickness (from 500 to 1,000 micrometres) can cause cracks to appear, and the color selection is generally limited to white matte finish.

Coatings are sometimes applied to copper.^[10][11] Clear coatings preserve the natural color, warmth and metallic tone of copper alloys. Oils exclude moisture from copper roofs and flashings and simultaneously enhance their appearance by bringing out a rich luster and depth of color. The most popular oils are Lemon Oil, U.S.P., Lemon Grass Oil, Native E.I., paraffin oils, linseed oil, and castor oil. On copper roofing or flashing, reapplication as infrequently as once every three years can effectively retard patina formation. In arid climates, the maximum span between oilings may be extended to from three to five years. Opaque paint coatings are used primarily for work applied over copper when substrate integrity and longevity are desired but a specific color other than the naturally occurring copper hues is required.^[12] Lead-coated copper coatings are used when the appearance of exposed lead is desired or where water runoff from uncoated copper alloys would ordinarily stain lighter-colored building materials, such as marble, limestone, stucco, mortar or concrete.^[13] Zinc-tin coatings are an alternative to lead coatings since they have approximately the same appearance and workability.^[14][15] (For more information, see copper in architecture: finishes.)

Maintenance

• A metal roof graded "AG" or "Utility" will need recoating once the factory finish wears off, or corrosion will occur. These paints are commonly acrylic or polyester based. Roof coatings are the preferred material since they are able to stay elastic and withstand the thermal cycling that occurs in metal roofs.
• Roofing materials made from stainless steel, zinc or copper will rarely require maintenance over their lifetime.^[16] Any required maintenance is usually due to design or installation mistakes. Otherwise, these materials commonly last over a century.
• Metal roofing with long life polymer coatings like Kynar should not normally require maintenance until the coating fails. These products have been used for over half a century now in the United States and few installations have failed. They should be considered lifetime products.
• To wash a metal roof, using water with a hose or power washer is sufficient; for more resistant dirt, a brush with detergent or trisodium phosphate is effective. Abrasive cleaners and tools such as wire brushes and steel wool, however, may damage the protective coating on a metal roof.^[17]

See also

• Corrugated galvanised iron
• Reflective surfaces (geoengineering)
• Green building
• Metal Building Manufacturers Association
• Metal Roofing Alliance
• Copper in architecture

References