Metal Roof Systems - Commercial
Learn More About Standing Seam Metal Roofs
Many different types of metal roof systems can be found on commercial structures. Standing seam metal roofs, coping, flat lock roof systems, flashings, perimeter edge metals, gutters and downspouts, and through wall scuppers are commonly fabricated and installed by roofing contractors. Metal is also used in flashings, trim, and copings. Metal systems are recommended by roofing professionals because of their longevity, durability, appearance, resistance to wind, reflectivity, and resistance to fire. Many metal roofs currently in service around the world have been in place for hundreds of years.
Featured Metal Roofing Project: Cabela's @ Liberty Township
The successful installation of a metal roofing system begins with several design considerations, including the following:
- Roof Pitch – Standing seam metal roofs are typically recommended on slopes greater than 3/12. Flat lock roofs are recommended on slopes 3/12 or less.
- Type of Metal – Dissimilar metals can corrode when they come in contact with one another or drain on each other. Also, some metals are naturally weathering while others require painting.
- Thickness of Metal – The gauge or weight of metals must be considered for different types of installations and applications.
- Interior Building Conditions – Vapor barriers or corrosion protection on the underside of the roofing panels must be considered if vapor is able to infiltrate the roof panels.
- Type of Fastener – Rivets, nails, and screws used in metal roofing applications must be compatible with the metal being installed.
- Thermal Movement – Metal, like all building materials, expands and contracts when exposed to changes in temperature. Metal roofs and box gutter liners can fail if the panels are not secured in one direction and able to float in the other.
- Underlayment and Slip Sheets – Combinations of Rosin paper, asphalt felt, and (high temperature) ice and water shield are used to allow the metal panels to expand and contract without tearing the underlayment. The low melting point of the asphalt must also be considered as some metal systems can reach temperatures of 200 degrees Fahrenheit.
- Metal Finish - Factory applied paint finishes for steel or aluminum are available in a wide variety of colors. Metal roof systems installed on churches, schools, or other historical buildings commonly use naturally weathering metals such as copper, stainless steel, or zinc.
After a proper design is specified, a skilled sheet metal foreman will install the metal system.
Standing Seam Metal Roofs
Metal standing seam roofs are either considered architectural or structural. Architectural panels are installed over a solid substrate while structural panels can be installed directly to purlins other types of framing. Structural panels must have a minimum thickness of 24 gauge steel.
Standing seam roofs should be installed with concealed fasteners to eliminate the risk of water infiltration at the fasteners. The panels are installed with seam heights of 1 to 2 inches. The seams enable thermal movement within the metal panels, add structural support to the system, and provide a water tight seal. Pre-painted metal panels come in a wide range of color options and can be fabricated from steel or aluminum. Factory applied paint systems will perform much better than field applied paint systems.
Flat Lock Metal Roofs
Commercial Flat lock roofing systems are fabricated out of copper, galvanized steel, and stainless steel. These types of roofs are commonly found on historical structures with cupolas, domes, spires, and low sloped roof areas. Metal panels are fabricated in a sheet metal shop with four interlocking seams, two bent upward and two bent downward. Panels should not be larger than 18 inches by 24 inches and secured to the roof deck with metal clips to prevent thermal movement from damaging the metal or the seams. Flat locked seams must be soldered on all roofs with a slope less than 8/12.
Gutters and Downspouts
Commercial gutters and downspouts are commonly fabricated from 24 gauge pre-finished steel or .040 pre finished aluminum. Shop fabricated gutters and downspouts are typically fabricated in 10 foot lengths and the seams are mechanically attached and sealed. Expansion joints should be installed on commercial gutter systems with lengths greater than 40 feet.
Commercial gutter and downspout sizes are determined by the roof surface area, slope of the roof system, and the historical rainfall data. Common commercial gutter sizes range from 7 inches to 10 inches in diameter. Commercial downspouts are usually rectangular in shape and can be found in sizes up to 4 inches x 6 inches.
For information about built up gutter systems, box gutters, and/or box gutter liners Click Here.
The following types of metals are commonly used in roofing systems:
Steel is the most common metal used in commercial roofing because of its strength and cost effectiveness. Steel is a metal alloy that consists of 98% iron and 2% carbon. Steel that is used for commercial metal roofing is pre-painted to reduce corrosion. Steel used in commercial roofing applications are most commonly available in thicknesses of 24 gauge.
Galvalume is a steel product that contains both aluminum and zinc. Galvalume out performs galvanized steel in commercial low sloped roof systems because of its corrosion resistance.
Aluminum is a corrosion resistant material that can be used to install standing seam roof systems. Aluminum has a very high rate of thermal expansion and contraction relative to other metals. For this reason, emphasis must be placed on proper design when aluminum is specified on roofing projects. Aluminum used in roofing is pre-painted in a variety of colors. Aluminum coil is measured by its thickness in inches. Common thickness for commercial roofing is at least .040 inches for metal copings and gutters.
Copper Roof systems are known for their durability, longevity, and beauty. Copper sheets used for residential and commercial roofing applications are measured in ounces per square foot instead of thickness. The most common copper weights in commercial applications 20 and 24 ounces per square foot. Copper is easily soldered and requires very little maintenance. Copper is a very soft (malleable) metal and lacks the strength that other metals possess.
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