Galvanization (or galvanisation) is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting. The term is derived from the name of Italian scientist Luigi Galvani.
Although galvanization can be done with electrochemical and electrodeposition processes, the most common method in current use is hot-dip galvanization, in which steel parts are submerged in a bath of molten zinc.
In current use, the term refers to the coating of steel or iron with zinc. This is done to prevent rusting of the ferrous item. The value of galvanizing stems from the corrosion resistance of zinc, which, under most service conditions, is considerably greater than that of iron and steel. The zinc serves as a sacrificial anode, so that it cathodically protects exposed steel. This means that even if the coating is scratched or abraded, the exposed steel will still be protected from corrosion by the remaining zinc – an advantage absent from paint, enamel, powder coating and other methods. Galvanizing is also favored as a means of protective coating because of its low cost, ease of application and comparatively long maintenance-free service life.
The term galvanizing, while technically referring specifically to the application of zinc coating by the use of a galvanic cell (also known as electroplating), is also generally understood to include hot-dip zinc coating. The practical difference is that hot-dip galvanization produces a thick, durable and matte gray coating – electroplated coatings tend to be thin and brightly reflective. Due to its thinness, the zinc of electroplated coatings is quickly depleted, making them unsuitable for outdoor applications (except in very dry climates). When combined with subsequent painting (which slows zinc consumption), electroplating is durable enough to be used in some premium auto body coatings.
Nonetheless, electroplating is used on its own for many outdoor applications because it is cheaper than hot dip zinc coating and looks good when new. Another reason not to use hot dip zinc coating is that for bolts and nuts size M10 or smaller, the thick hot-dipped coating fills in too much of the threads, which reduces strength (because the dimension of the steel prior to coating must be reduced for the fasteners to fit together). This means that for cars, bicycles and many other ‘light’ mechanical products, the alternative to electroplating bolts and nuts is not hot dip zinc coating but making the bolts and nuts from stainless steel (known by the corrosion grades A4 and A2).
Electroplated steel is visually indistinguishable from stainless steel when new. To determine whether a part is electroplated or stainless steel, apply a magnet. The most common stainless steel alloys (including those used for bolts and nuts) are not magnetic or only very slightly attracted to a magnet.
Originally, “galvanization” was the administration of electric shocks (in the 19th century also termed Faradism, after Michael Faraday). It stemmed from Galvani’s induction of twitches in severed frogs’ legs, by his accidental generation of electricity. Its claims to health benefits have largely been disproved, except for some limited uses in psychiatry in the form of electroconvulsive therapy (ECT). This archaic sense is the origin of the meaning of galvanic when meaning “affected/affecting, as if by a shock of electricity; startled”. and the metaphorical “galvanize into action” referring to suddenly stimulating a complacent person or group to take action. Later the word was used for processes of electrodeposition, which remains a useful and broadly applied technology. But the term “galvanization” has largely come to be associated with zinc coatings, to the exclusion of other metals.
Galvanic paint, a precursor to hot-dip galvanization, was patented by Stanislas Sorel, of Paris, France in December, 1837.
The earliest known example of galvanizing of iron was found 30 September 1999 by the Royal Armouries Museum on a 17th century Indian armor in their collection.
Main articles: Hot-dip galvanizing and Sherardizing
Zinc coatings prevent corrosion of the protected metal by forming a physical barrier, and by acting as a sacrificial anode even if this barrier is damaged. When exposed to the atmosphere, zinc reacts with oxygen to form zinc oxide, which further reacts with water molecules in the air to form zinc hydroxide. In turn, zinc hydroxide reacts with carbon dioxide in the atmosphere to yield a thin, impermeable, tenacious and quite insoluble dull gray layer of zinc carbonate which adheres extremely well to the underlying zinc, so protecting it from further corrosion. This is similar to the protection afforded to aluminium and stainless steels by their oxide layers.
Hot-dip galvanizing deposits a thick robust layer that may be more than is necessary for the protection of the underlying metal in some applications. This is the case in automobile bodies, where additional rust proofing paint will be applied. Here, a thinner form of galvanizing is applied by electroplating, called “electrogalvanization”. The hot-dip process slightly reduces the strength of the base metal, which is a consideration for the manufacture of wire rope and other highly-stressed products. The protection provided by this process is insufficient for products that will be constantly exposed to corrosive materials such as salt water. For these applications, more expensive stainless steel is preferred. Some nails made today are electro-galvanized.
As noted previously, both mechanisms are often at work in practical applications. For example, the traditional measure of a coating’s effectiveness is resistance to a salt spray. Thin coatings cannot remain intact indefinitely when subject to surface abrasion, and the galvanic protection offered by zinc can be sharply contrasted to more noble metals. As an example, a scratched or incomplete coating of chromium actually exacerbates corrosion of the underlying steel, since it is less electrochemically active than the substrate.
Galvanized surface with visible spangle
The size of crystallites in galvanized coatings is a visible and aesthetic feature, known as spangle. By varying the number of particles added for heterogeneous nucleation and the rate of cooling in a hot-dip process, the spangle can be adjusted from an apparently uniform surface (crystallites too small to see with the naked eye) to grains several centimetres wide. Visible crystallites are rare in other engineering materials.
Thermal diffusion galvanizing, a form of Sherardizing, provides a zinc coating on iron or copper based materials partially similar to hot dip galvanizing. The final surface is different than hot-dip galvanizing, in that all of its zinc is alloyed. Zinc is applied in a powder form with “accelerator chemicals” (generally sand, but other chemicals are patented). The parts and the zinc powder are tumbled in a sealed drum while it is heated to slightly below zinc’s melting temperature. The drum must be heated evenly, or complications will arise. Due to the chemicals added to the zinc powder, the zinc/iron makes an alloy at a lower temperature than hot dip galvanizing. This process requires generally fewer preparatory cleanings than other methods. The dull-grey crystal structure formed by the process bonds more strongly with paint, powder coating, and rubber overmolding processes than other methods. It is a preferred method for coating small, complex-shaped metals, and for smoothing in rough surfaces on items formed with powder metal.
Rusted corrugated steel roof
Although galvanizing will inhibit attack of the underlying steel, rusting will be inevitable, especially if exposed to the natural acidity of rain. For example, corrugated iron sheet roofing will start to degrade within a few years despite the protective action of the zinc coating. Marine and salty environments also lower the lifetime of galvanized iron because the high electrical conductivity of sea water increases the rate of corrosion. Galvanized car frames exemplify this; they corrode much quicker in cold environments due to road salt. Galvanized steel can last for many years if other means are maintained, such as paint coatings and additional sacrificial anodes.
See also: Galvanic corrosion
In the early 20th century, galvanized piping replaced cast iron and lead in cold-water plumbing. Typically, galvanized piping rusts from the inside out, building up plaques on the inside of the piping, causing both water pressure problems and eventual pipe failure. These plaques can flake off, leading to visible impurities in water and a slight metallic taste. The life expectancy of such piping is about 70 years, but it may vary by region due to impurities in the water supply and the proximity of electrical grids for which interior piping acts as a pathway (the flow of electricity can accelerate chemical corrosion). Pipe longevity also depends on the thickness of zinc in the original galvanization, which ranges on a scale from G40 to G210, and whether the pipe was galvanized on both the inside and outside, or just the outside. Since the World War II, copper and plastic piping has replaced galvanized piping for interior drinking water service, but galvanized steel pipes are still used in outdoor applications where mechanical strength is required.
This lends some truth to the urban myth that water purity in outdoor water faucets is lower, but the actual impurities (iron, zinc, calcium) are harmless. This is not always the case in pre-1986 copper pipe where lead-containing solder was commonly used. In installations where copper pipe has been fitted to replace a section of corroded galvanized pipe, a special dielectric fitting called a “union” must be used to join the two types of pipes; otherwise the presence of water in contact with differing metals creates an electrical current that can cause “galvanic corrosion”. In some amateur installations, the failure to use this special fitting has caused the lead in the solder to leach into the drinking water. A common location where this occurs is where a home’s copper piping connects to a galvanized steel municipal supply line.
The presence of galvanized piping detracts from the appraised value of housing stock because piping can fail, increasing the risk of water damage. Galvanized piping will eventually need to be replaced if housing stock is to outlast a 50 to 70 year life expectancy, and some jurisdictions require galvanized piping to be replaced before sale. One option to extend the life expectancy of existing galvanized piping is to line it with an epoxy resin.
ZINCALUME / GALVALUME
Galvalume® sheet is used for two broad categories of roofing: nonresidential and residential. For nonresidential roofing, bare or unpainted Galvalume® sheet is used for low slope, concealed fastener standing seam roofs (SSR) as a replacement for nonmetallic built-up, rubber and ballasted nonmetallic roofs and for steeper slope screw-down roofs with exposed fasteners. Prepainted Galvalume® sheet is mostly used for steep slope architectural roofing and mansards to enhance the appearance of the building using color, form and texture. Nonresidential roofs can be new or retrofit over both old steel and nonmetallic roofs. For residential roofs, prepainted Galvalume® sheet is generally used, although some architects and home owners use bare Galvalume® sheet because they like the look of its bright metallic surface. Galvalume® residential roofs can be new or retrofitted over old roofs.
• 1. Why is Galvalume® sheet called by other names? Are all of these products the same?
• 2. How is it made?
• 3. Why is it a good material for roofing?
• 4. Galvalume® sheet is sold with AZ50 and AZ55 designations. What do they mean?
• 5. What is the reflectivity of Galvalume® sheet?
• 6. What are the advantages of a Galvalume® standing seam roof (SSR) compared to a built-up roof?
• 7. Can a Galvalume® SSR be installed over an old flat built-up roof?
• 8. Are Galvalume® roofs offered with a warranty?
• 9. How does the corrosion resistance of Galvalume® sheet compare with that of galvanized sheet, and how long can a Galvalume® sheet roof be expected to last?
• 10. Should architectural Galvalume® sheet roofs be installed on decking or over shingles on residential applications?
• 11. What types of insulation are recommended for Galvalume® roofs? Are there any to be avoided?
• 12. What types of flashing are recommended for bare and/or painted roofs?
• 13. What are the differences between Galvalume® roof systems that use concealed and exposed fasteners?
• 14. Galvalume® sheet can be attacked by concrete and mortar. How are such attacked areas on Galvalume® roofing and siding best repaired?
• 15. Can I place bare or prepainted Galvalume® sheet in contact with the concrete foundation footer?
• 16. What is the life of a prepainted Galvalume® roof or wall?
• 17. Can pressure-treated wood be used in contact with bare and prepainted Galvalume® sheet?
• 18. Where can I buy a Galvalume® roof and how can I get a list of Galvalume® roof suppliers for my area?
• 19. How do the costs of both new and retrofit low slope Galvalume® standing seam roofs compare with traditional flat nonmetallic roofs?
Why is Galvalume® sheet called by other names? Are all of these products the same?
The product is a 55% aluminum-45% zinc alloy coated sheet steel developed by Bethlehem Steel and sold commercially under the trademark Galvalume®, starting in June 1972. Bethlehem Steel later licensed other major steel companies to produce and sell the product using its patents and technology. In North America, the Galvalume® trademark is used by Bethlehem Steel, Dofasco Inc. (Canada), National Steel Corp., U.S. Steel and Wheeling-Nisshin, Inc. In Central and South America, Industrias Monterrey (Mexico) markets the product under the trademark Zintro-Alum, while Galvak S.A. de C.V. uses the trademark Galval. Steelscape, Inc. uses the trademark ZINCALUME®. All of these products are the same generic 55% Al-Zn coated shee steel made by the same process using the same technology.
How is it made?
Both Galvalume® and galvanized sheet steels are made by a “continuous hot dip” process. Coils of cold rolled steel are welded end-to-end and processed continuously on the coating line at speeds up to 600 feet per minute. The uncoiled sheet is first cleaned to remove rolling oils and mill dirt, and to reduce surface oxides so that the surface will accept the coating. These continuous sheets are first fed into a molten coating bath contained in an open top, brick-lined heated pot. The sheet then passes around a roller submerged in the coating bath and exits the bath vertically, pulling out with it an envelope of the coating material. As it exits, the sheet proceeds through a pair of opposing air knives, which are positioned above the bath and equidistant from the surface of the sheet. Most modern production lines have a coating thickness gauge feed-back control, which automatically adjusts knife air pressure and position to ensure that a uniform coating is applied. Various finishing steps are carried out to complete the process, after which the sheet is wrapped around a reel into a coated steel coil.
Why is it a good material for roofing?
Galvalume® sheet is an ideal material for roofing because of its extraordinary outdoor corrosion resistance and resulting long life. It can be readily rollformed into a variety of panels, as well as formed and stamped into tile and shingle facsimiles. It can also be factory painted to impart color and extend durability. Most important, it can be used in modern day steel roof designs which are strong, yet light weight. And unlike conventional nonmetallic roof systems, Galvalume® sheet roofs won’t crack and peel when subjected to the sun and weather.
Galvalume® sheet is sold with AZ50 and AZ55 designations. What do they mean?
Galvalume® sheet is made to meet ASTM Specification A792. This specification covers a number of requirements, including coating weight. AZ50 and AZ55 are the English unit coating weight designations indicating that, respectively, 0.50 ounces per square foot and 0.55 ounces per square foot of the aluminum-zinc alloy coating have been applied to both sides of the Galvalume® sheet. Converting these coating weights to coating thickness, AZ50 is equivalent to about 0.8 mil (0.0008″) on each side of the sheet, and AZ55 to about 1.0 mil (0.001″) on each side. In metric units, AZ150 is equivalent to about 20 microns and AZ155 to about 25 microns on each side.
What is the reflectivity of Galvalume® sheet?
Galvalume® sheet has good heat and sunlight reflectivity. Its bright, white reflective surface makes it an ideal material for roofing. During the summer it makes buildings cooler by efficiently reflecting away sunlight and reducing the amount of heat transmitted into the building. Likewise, it makes buildings warmer in the winter by reflecting inside heat from the underside of the roof back into the building. This good thermal reflectivity translates into energy savings by reducing cooling costs in the summer and heating costs in the winter. Tests have shown that only half as much heat from solar radiation is transmitted into a building fitted with a Galvalume® roof compared to a galvanized roof, and almost one-third less heat compared to a terra-cotta roof.
What are the advantages of a Galvalume® standing seam roof (SSR) compared to a built-up roof?
Leaking conventional, flat nonmetallic roofs are the biggest problem on nonresidential buildings for architects and building owners. Conventional roofs made with organic materials deteriorate even under normal environmental conditions. They embrittle from the heat and ultraviolet radiation from the sun. Then, as result of temperature fluctuations, they develop cracks, splits and tears. Finally, because they are flat, ponding water inevitably penetrates these brittle, cracked systems and leaks into the building, causing damage to goods and disrupting activities inside the structure. Leaks can be patched early in the life of the roof, but as time passes, leaks become more frequent and an expensive replacement of the roof is required. Such replacements often require tearoff, extra labor and even a temporary building shut-down. Galvalume® standing seam roofs (SSR) offer a weathertight, maintenance-free roof system that will last for decades on commercial, office and factory buildings. Galvalume® SSRs are economical to install, leak proof, maintenance-free, energy efficient, noncombustible and long-lived.
Can a Galvalume® SSR be installed over an old flat built-up roof?
A Galvalume® SSR is an ideal system for retrofit roofing. Its light weight makes it suitable for retrofit applications over any old, leaking, conventional, nonmetallic roof system. Retrofitting is accomplished by installing to the existing roof structure a light weight sub-framing system, generally made with light structural steel sections, that provides a minimum ¼:12 slope for the new Galvalume® SSR. By installing the roof directly over the existing nonmetallic roof, costly and time-consuming tear-offs are eliminated, and activities inside the building can continue without interruption.
Are Galvalume® roofs offered with a warranty?
Regarding warranties, a purchaser needs to consider the two types of Galvalume® roofs that are used — structural and architectural systems. Structural systems are those, such as SSR, that are installed directly on the roof structural system (i.e., purlins), without decking. These are low slope systems, up to about 1:12 pitch, using bare, heavier gauge Galvalume® steel sheet. Use in this application is guaranteed for 20 years. (Some roofing manufacturers also warrant their roof systems for weather tightness.)
Architectural Galvalume® roofs are those used in applications in which the roof is being used not only for protection against the weather, but also for its appearance. Because architectural roofs are visible from the ground, they are used as a design feature of the building. Such systems are used at high slopes, usually up to 4:12, for both residential and nonresidential buildings. In most cases the Galvalume® panels are prepainted in a wide range of colors using today’s high performance paint systems.
Warranties cover both the Galvalume® sheet and the paint system. Most Galvalume® producers give the same warranty for the Galvalume® steel substrate for prepainted roofing as that for bare roofing. Most producers also give a 5 year warrantee against chalk, fade and peel of the paint system. Paint companies and coil coaters typically extend the paint warranty as much as five years beyond the 20 year Galvalume® sheet producer warranty, depending upon the paint system and environmental conditions. Galvalume® sheet producers and roof manufacturers should be contacted for specific requirements for their warranties.
How does the corrosion resistance of Galvalume® sheet compare with that of galvanized sheet, and how long can a Galvalume® sheet roof be expected to last?
Galvalume® sheet has been successfully used in roofing applications for more than 25 years; it has been evaluated in outdoor R&D tests for well over 30 years. Based on these tests, in which corrosion weight losses were measured and compared with galvanized, Galvalume® sheet is projected to outlast galvanized sheet (with an equivalent coating thickness) in various atmospheres by up to nine times. Likewise, recent inspections of 82 low slope Galvalume® roofs up to 22 years old in the eastern U.S. confirms the R&D results. These roofs are in excellent condition and are projected to last 30 to 40 years before requiring major maintenance.
Should architectural Galvalume® sheet roofs be installed on decking or over shingles on residential applications?
Wood or steel decking is normally used for prepainted Galvalume® architectural roof systems on both residential and nonresidential applications, but it is not recommended to install the panels in direct contact with the decking. Instead, 30 pound felt, or an equivalent, should first be installed on the decking and the roof panels then installed over the felt. For residential applications, the roof panels would be installed over roofing felt on wood decking for new construction applications, or in applications in which the old shingles would be removed from the deck.
Roofing manufacturers should be contacted for design and installation details both in warmer regions where condensation can occur under roof panels, and also in cold regions where snow, ice and water can collect at eaves and valleys and leak into the building.
What types of insulation are recommended for Galvalume® roofs? Are there any to be avoided?
By far, fiberglass roll insulation is the most commonly used insulation for Galvalume® steel roofs on nonresidential buildings. It can be used in any of the available thicknesses to give the required insulation value. One of the main benefits of retrofitted Galvalume® roofs installed over leaking nonmetallic flat roofs is the ability to add insulation under the new Galvalume® roof and realize significant energy savings from reduced heating and cooling requirements. In such instances, fiberglass roll insulation can either be placed on top of the old nonmetallic roof or under the new retrofit roof.
Wet insulation, which may be rain soaked at the site or wet from condensation or a leak in the roof, should not be in contact with Galvalume® roof panels. Insulation should be dry when installed and kept dry after installation. Fiberglass insulation retains water and can cause rapid inside-out corrosion on Galvalume® sheet panels. Also, spray-on insulation is sometimes used inside buildings under roofs and on siding. This insulation may contain fire retardant chemicals that can be corrosive to Galvalume® sheet. Manufacturers should be consulted about such fire retardant additives if spray-on insulation is used.
What types of flashing are recommended for bare and/or painted roofs?
Because Galvalume® sheet can be expected to provide long life, flashing should be used that will provide a life commensurate with that of Galvalume® sheet. For bare Galvalume® sheet roofs, Galvalume® sheet flashing is preferred, although aluminum flashing is also acceptable. Galvanized flashing is not recommended because it will not provide comparable corrosion resistance. Copper and lead are not recommended for flashing in direct contact with Galvalume® roof panels because they will cause galvanic corrosion of the Al-Zn coating. For prepainted Galvalume® sheet roofs, flashing as well as trim parts should preferably be made from prepainted Galvalume® sheet from the same color and coil line batch for both initial color matching and long term color change during weathering.
What is the difference between Galvalume® roof systems that use concealed and exposed fasteners.
There are a number of variations of concealed fastener systems. For low slope structural systems, panels are overlapped and lockformed or snapped together at the seams and held down with clips, one end of which is overlapped in the seam and the other end fastened to the structural member of the roof. The clips have a sliding feature that permits the roof panels to “float” during expansion and contraction from ambient temperature changes.
Exposed fastener systems use fasteners that are driven through the top side of the roof panel into a deck. These systems are designed for high slope applications for both bare and prepainted Galvalume® roofs. Panel lengths are typically short on these systems because they do not provide for expansion and contraction from temperature changes. These systems also require many overlapping joints which must be properly sealed to avoid crevice corrosion.
Galvalume® sheet can be attacked by concrete and mortar. How are such attacked areas on Galvalume® roofing and siding best repaired?
The aluminum-zinc coating on Galvalume® sheet suffers fairly rapid corrosion in highly alkaline environments, such as concrete. The coating is attacked during the setting period when buried in concrete, and can also be attacked from mortar splashes and droppings during masonry installation. The best repair for attack from mortar splashing is to cover the affected area with a protective coating. On bare Galvalume® roof panels, successful results have been obtained with Unilflex 500, an asphalt-based, fiber aluminum system available from Kool Seal, Inc. Repair of prepainted Galvalume® should done using the same type finish coats that are applied on the coil coating line. In all cases, the surface should be clean and dry and manufacturers’ instructions should be followed.
Can I place bare or prepainted Galvalume® sheet in contact with the concrete foundation footer?
Direct contact with the concrete footer is not recommended for either bare or prepainted Galvalume® sheet. Water can accumulate at the crevice between the Galvalume® panel and the footer, causing corrosion at the cut edge. Ideally, sill plates should be used on concrete foundations to avoid direct contact with the foundation and to drain water away from the edge of the panel. Also, the siding panel should not be in contact with the sill plate. Sill plates should be tilted slightly away from the building to avoid trapping water and providing for drainage away from the edge of the panel.
The footer also is an area where fiberglass blanket insulation should be installed properly. Insulation needs to be installed above the sill so that it won’t get wet and act as a wick to cause inside-out corrosion. To avoid wet insulation at the footing, several inches of fiberglass insulation should be removed from the waterproof vapor barrier at the end of the blanket. The vapor barrier should then be folded up and around the insulation and placed between the panel and the sill plate, thereby eliminating contact of the fiberglass insulation with any water that may accumulate in this area.
What is the life of a prepainted Galvalume® roof or wall?
From a practical standpoint, the life of a prepainted Galvalume® panel is dictated by the performance of the paint film, i.e., appearance as affected by conditions of fade, chalk and peel, and the life of the paint film is determined by the type of paint system and the weathering conditions to which it is exposed. Almost all building owners will repaint a prepainted roof or sidewall when the appearance of the paint film is determined to be aesthetically unattractive from weathering.
Paint systems applied on modern coil coating lines can be expected to provide good to excellent performance in nearly every environment. The most commonly used topcoats are acrylics, polyesters, siliconized polyesters, fluoropolymers and plastisols. When combined with chemical pretreatments and high-performance primers, these topcoats enhance adhesion of the paint film to the metal coating and increase overall corrosion resistance, particularly at cut edges, scratches and bends.
Can pressure-treated wood be used in contact with bare and prepainted Galvalume® sheet?
Contact with pressure-treated wood or, for that matter, any wet lumber is not recommended for either bare or prepainted Galvalume® sheet. Treated lumber contains chemicals that protect the wood when buried in soils. Direct contact between wet treated lumber and Galvalume® sheet creates a corrosion cell and the corrosive chemicals leaching out of from the wood accelerates this process. All rooftop ancillaries, such as air conditioners, should be mounted with factory-made mounting accessories compatible with Galvalume® sheet (roof curbs, for example). Some HVAC contractors commonly mount rooftop air conditioners on pressure treated landscape ties. Direct contact of these ties with the Galvalume® roof causes corrosion of the aluminum-zinc coating. Even drainage from pressure treated lumber onto Galvalume® sheet should be avoided.
Where can I buy a Galvalume® roof and how can I get a list of Galvalume® roof suppliers for my area?
The best way to buy a Galvalume® steel roof is through the roof panel manufacturers. The major manufacturers have regional sales offices and manufacturing plants throughout North America. They also have qualified and affiliated contractors who are trained and approved to install their roof systems. It’s important that only experienced and approved contractors be used to install Galvalume® roof systems. The Galvalume® Sheet Producers of North America, located in Vancouver, WA, can be contacted at 360-750-5791 to obtain this list of licensed manufacturers. Also, an online directory of Galvalume® roof manufacturers, grouped by region, can be found by selecting the “Where to Buy” button located on the tool bar. Using a simple search engine, visitors can view and then print a list of manufacturers in their region who can, in turn, refer the visitor to an affiliated contractor.
How do the costs of both new and retrofit low slope Galvalume® standing seam roofs compare with traditional flat nonmetallic roofs?
The many benefits offered by new and retrofit Galvalume® standing seam roofs (SSR) over traditional nonmetallic roofs translate into both direct and indirect cost savings. A retrofit Galvalume® SSR installed on a light weight structural system over an old, leaking nonmetallic roof is a lower cost long term alternative and, in many cases, a lower initial cost alternative if tear-off of the old nonmetallic roof is required. Benefits that translate into related cost savings result from the installation of additional insulation under the Galvalume® SSR, avoiding tear-off so that activities inside the building are not disrupted and disposal of nonmetallic material is not necessary, and the ability to schedule retrofit installations on a year-round basis in almost all climates.
The initial cost of a new, low slope Galvalume® standing seam roof will generally be more expensive than a traditional flat nonmetallic roof, such as a built-up roof. However, if long term life cycle cost is considered, say, up to 25 or 30 years, the Galvalume® SSR will cost less than a nonmetallic roof. That’s because initial repairs for leaks on nonmetallic roofs are not unusual after only 8 or 10 years, and replacement by tear-off may be required after about 15 to 20 years. So, over the long term, a new Galvalume® SSR will cost less than a traditional nonmetallic roof. This lowered life cycle cost, resulting from the minimal maintenance required by a Galvalume® roof, is what makes steel roofing an appealing, affordable and long-lasting alternative to traditional asphalt, wood, tile and slate roof coverings.
LINK TO ; http://en.wikipedia.org/wiki/Aluminium
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