Residential Metal Roof Systems
Various types of metal roofing systems can be found in residential structures. Two common types are standing seam metal roofs and flat lock metal roofs. Metal is also used in chimney flashings, wall flashings, trim, valleys, and box gutter liners. 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.
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. In most situations, copper and galvanized steel should not be used on the same roof system.
- Thickness of Metal – The gauge or weight of metals must be considered for different types of installations and applications. Copper is commonly used in weights of 16 ounces per sq foot or 20 ounces per square foot. Galvanized steel is measured by gauge. 26 gauge steel is thicker than 28 gauge steel (Lower gauges are thicker than higher ones). Aluminum is measured in inches. Common thicknesses of aluminum (from thinnest to thickest) include .019, .024, .027, and .032.
- Interior Building Conditions – Vapor retarders or corrosion protection for the underside of the roofing panels must be considered if vapor is able to infiltrate the roof panels. Effective vapor retarders include self-sealing ice and water guard or synthetic underlayment.
- Type of Fastener – Rivets, nails, and screws used in metal roofing applications must be compatible with the metal being installed. For example, Galvanized roofing fasteners should be used with galvanized steel panels, and copper or stainless steel fasteners should be used with copper panels. Careful consideration should also occur when fasteners penetrate treated wood.
- 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 thermal movement is restricted. (Please see the article below that appeared in Professional Roofing magazine.)
- Underlayment and Slip Sheets – Combinations of Rosin paper, asphalt felt, and (high temperature) ice and water guard 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 – Three types of metal finishes can be installed on residential structures – naturally weathering metals, factory-applied painted systems, and field applied pre-painted systems. Naturally weathering (and corrosion resistant) metals include copper, stainless steel, and zinc. These metals do not require a painted finish as they oxidize to form a protective coating or patina. The seams on these systems are soldered. Pre-painted systems include steel and aluminum. It’s important to note that one drawback to these systems is that seams cannot be soldered and must be sealed using caulk. Field painted finishes include galvanized steel systems. Galvanized steel seams are soldered and then base metal can be painted to eliminate corrosion.
After a proper design is specified, a skilled sheet metal foreman will install the metal system. These individuals must be skilled at soldering to successfully install flat lock metal roofs, box gutters, and flashings. Solder is used to fuse metal seams together to ensure that they are watertight. Deer Park Roofing does not recommend the use of caulk as a substitute for solder.