Metal roof
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A metal roof, often referred to as a tin roof, is a roofing system made from metal pieces or tiles. It is a component of the building envelope.
Contents
History
Metal roof sheeting in the form of Corrugated galvanized steel was a great aid to opening up America in its early days. This is still happening today in parts of the developing world.
Specifications of a metal roof
- Light Weight
- Portability
- Durability. The lowest end metal roofing (thin gauge with acrylic or polyester paints) commonly called AG (agricultural) or Utility panels will last 20–30 years which is roughly 2 times the lifespan of an average asphalt roof. Most metal roofing products today come with warranties from 25 to 50 years. Sheet materials like stainless steel, copper, zinc and aluminum are inherently durable; the oxidization of the base material forms a protective patina. Some modern steel roof sheeting materials are coated with an alloy of zinc and aluminum to give it some of the durability of each of those materials at a lower cost and higher strength than either. Copper and Zinc details have historically been proved to last upwards of 100 years with little or no maintenance. The average life-span of asphalt shingles today (since 2001) is 6–9 years [citation needed], while residential and commercial grade metal roofing usually lasts from 50-100+ years, depending on the type. The coatings and fixings on steel roof sheeting can be designed for different environments including industrial and marine locations.
- Metal roofs are often used to cover large buildings because of their high strength to weight ratio. The roof of the new Wembley Stadium is an example. It consists of approximately 40,000 sq ft (3,700 m2) steel sheeting.
- Fire and spark resistant.
- Hail resistant.
- Wind resistant.
- Snow shedding: Painted metal roofs are usually snow-shedding. Snow can usually collect when it is fresh and lighter weight. As soon as the ambient temperature rises a couple degrees, the snow usually just slides off. For this reason metal roofing is ideal for homes in northern or mountain regions.
- Metal is readily recyclable. Aluminum and copper roofing products are available with over 95% recycled content. Most metals can be recycled over and over without losing any valuable properties. Recycling is very efficient. As an example: recycled Aluminum only requires 5% of the energy to produce as does new Aluminum.
- Design flexibility: Some Steel roofing products can be installed over open framing, or on a solid substrate.
- Large sprung curves.
- Rolled bull-nose shapes.
- Energy efficiency. Coatings with high reflectivity like Kynar with "cool roof" pigments commonly save 20-30% on air-conditioning costs due to reflecting away much of the sun's heat. Increases the thermal efficiency of buildings in high temperature areas with its cool-roof paints and high emissivity.
- Labor efficient
- Most metal roofing products require very little or no maintenance.
Disadvantages
- Care must be taken on large roofs to provide for thermal movement.
- Movement caused by differences in temperature may cause objectionable noises in some roofs, for example curved roof surfaces. But in roofing this is a rare phenomenon not commonly experienced.
- Care must be taken with all metal roof products to avoid incompatible materials. Dissimilar metals can cause unexpected and rapid corrosion.
- Metal refining and production and transport of metal roof components can be energy-intensive and almost always a non-local activity. The flipside of this is the relatively clean and energy saving process of metal recycling. Some of the metals that are used today like Aluminum and Copper are routinely over 80% recycled content. Even 200 year old Copper can be easily and inexpensively recycled.
- Expensive[citation needed]
Applications of Metal Roofing
- Metal Roofing is a very versatile building material. It is durable. It can be used on residential, commercial, industrial or agricultural buildings. It is not only used in roofing applications, but also may be used as a wall covering. There are many different profiles and styles available to fit most every building situation.
- One may also combine shapes for aesthetic impact. Using the same material and same color but different shapes can have an impact on curb appeal and building value. Alternativly different metals can be used to create interesting colour combinations.
Metal roofing in New Construction
Metal roofing is ordered per each piece, whether it is in sheet form, trim or ridge material. When properly estimated there is very little waste material in a new project. Sheets can be ordered and cut to exact lengths, allowing for less on the job fabricating.
Metal roofing in Remodeling
Metal roofing is usually easily applied over an existing roof. Especially in situations where labor cost cutting is essential, the added value of not having to remove the existing roof material can be of a large help.
Metal Roof Material Types
- Corrugated galvanized steel 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 fore ground.
- A blend of Zinc, aluminum 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.
- Metal tile sheets, most often painted or stone-coated steel.
- Stainless steel. Available for harsh conditions and/or as distinctive design element. Usually roll-formed into standing seam profiles but shingles are available.
- 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. These properties help increase 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. Anodizing is imbedded in the grain of the metal and is not normally subject to weathering and wear.
- Copper - Usually used for flashing or smaller highly detailed areas like entryways and Bays. Expensive. At the Lyle Center for Regenerative Studies copper is used for regenerative principles of sustainable design: if the building were ever to be dismantled the copper would be reused because of its high value in recycling and variety of possible uses.
- Stone coated steel - Panels made from zinc/aluminum coated steel with acrylic gel coating. The stones are usually a natural product with a colored ceramic coating.
- IBR or Inverted Box Rib is a low-cost corrugated square-fluted iron roofing used mainly in the South African market. It can be commonly seen all the way from industrial sites to low-income shacks.
Metal Roof Coatings
Many different types of coatings are used to coat metal panels: anti-rust, waterproofing, heat reflective. They can be made of various materials such as epoxy, ceramic and since recently nanotechnology materials.
Metal sheet roofs are very affordable, durable and can be installed fast, which makes them extremely popular in the construction of commercial and industrial buildings. The major problem with metal roofs in warm weather is the fact that they absorb and retain enormous quantities of heat. In non-air-conditioned buildings, this translates directly into high building envelope heat loads, temperature and moisture build-up. For air-conditioned buildings, it means higher energy costs as the air-conditioning has to fight a heat that builds up continuously during the day, even if the sky is overcast (ultraviolet rays penetrate clouds, they are the major source of heat from solar radiations). Because buildings with metal roofs are hotter than their surroundings, they directly contribute to increasing the urban heat island effect. A metal sheet roof in tropical countries, for example, can be hotter than 75°C / 167°F.
Ceramic coatings are the most popular heat reflective coatings applied on metal sheet roofs worldwide. The technology is several decades old and was initially developed by NASA for the American space program. Most ceramic coatings are made from regular paint, to which ceramic beads are mixed as an additive. Although they reflect on average 75% to 85% of solar radiations, their performance tends to plummet by 30% and more after a couple of years because of dirt build-up. Their composition and thickness (from 500 microns up to 1,000 microns) can cause cracks to appear and they are available in very limited colors, mainly in white with a matte finish. This is why their application is mostly limited to industrial and commercial buildings. Their affordability however makes them a good choice as insulation for metal sheet roofs when investment cost is the main issue.
Nanotechnology solar reflective coatings are efficient heat reflective coatings that can be applied on roofing materials today. They are radiant barriers which performance increases exponentially with the surface's heat, which makes them perfect for application on metal sheet roofs. Heat load on buildings with metal sheet roofs is typically reduced by 30%, which instantly makes the building energy-efficient and caps heat build-up. Developers can leverage the affordability and wide availability of metal roofs while transforming them into a high performance heat shield. Traditional under-roof insulation such as PU foam or PE foam can add further to protection from heat.
This new generation of nanotechnology coatings also adds more value and benefits to metal sheet roofs:
- it extends their lifespan: since the metal expands and contracts less due to lower temperature variations, it causes less stress on bolts and joints. Risk of leaks is reduced, as is the need for maintenance
- coated metal sheet roofs are cool and reduce the urban heat island effect
- some nanotechnology coatings also include Titanium Dioxide, which makes them self-cleaning. Metal sheet roofs in industrial areas with lots of dust will remain clean longer are less sensitive to acids (such as the ones used in cooling towers). In coastal areas, these coatings protect the metal sheet from marine salt.[citation needed]
Maintenance
- When a Metal roof is used that is called an “AG” or “Utility” grade, these 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. Usually the maintenance is required due to design or installation mistakes as these materials can commonly last over a century.
- Metal roofing with long life paints like Kynar should not normally require maintenance until the paint fails. These products have been used for over half a century now in the U.S. and few installations have failed. So these roofing products should be considered a lifetime product.
See also
- Metal Roofing Alliance
- Corrugated galvanized iron
- Cool roof
- Green building
- Metal Building Manufacturers Association
References
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