| Metal Roofing can be a Good Alternative for Reconstructing a Roof |
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Despite their high initial cost, metal roofing is a durable, low-maintenance roof system building owners sometimes choose to remedy recurring roof problems.
With the invention of the standing-seam roof panel and floating roof concept in 1969, metal roofing became an economical alternative for re-roofing projects. Mechanical seaming and sealing technology reduced the minimum roof slope to ¼ inch per foot, the required minimum slope of competing systems. Reduced roof slope reduces building volume consequently lowering overall building cost. Their light weight makes metal roof systems a good choice when the building’s structural support system is limited.
Metal roofing systems are categorized according to their function: structural or architectural; floating or fixed. Structural standing-seam metal roof identifies a panel able to counter both gravity and wind-uplift loads. The panels may span more than 3 feet between structural supports. Architectural panels require a steep slope (25 percent or more) and are not part of the structural system of the building. Architectural panels are affixed to a solid deck with felts placed between the deck and panels to enhance water-shedding performance. In a fixed system, fasteners are placed at regular intervals through the metal panels’ end and side laps. Thermal movement of the metal panels elongates fastener holes making fastener holes a primary leak source. A floating system fixes the panels at a single location along the panel’s length. A metal clip is used to attach metal panels to structural supports. The clips accommodate thermal expansion or contraction of the panel. Despite their high initial cost, metal roofing is a durable, low-maintenance roof system building owners sometimes choose to remedy recurring roof problems. Metal roofs may offer the lowest long-term lifecycle cost of any competing roof system. Their initial cost ranges up to three times the cost of competing roof systems, but their long service life and lower operating and maintenance costs offset initial cost. A lifecycle analysis should be done to quantify costs, both initial long-term, between different roof systems. However, multiple roof penetrations, complex building shapes, or custom-designed flashing details are difficult challenges for metal roof systems. Metal roofs may be recycled. At the end of their service life, 25 to 95 percent of the material may be recycled, making it a green-friendly roof. Flashings are the most critical component for a metal roofing system. Metal panel ribs must be parallel to the roof slope. The ribs must be stopped short of downhill obstacles to divert water around roof projections. The flashings must be designed to account for both thermal movement and channeled-water flow. A metal roof must be able to accommodate thermal movement up to 2 inches. Expansion and contraction of the metal roof system is a major design consideration. Roof leaks in metal roof systems most often occurs at panel joints or terminations. Closures need to be watertight not just water-shedding. Vertical and horizontal seams require inspection. Sealants should be present in panel seams. A heavy rain or snow leading to ice damming may submerge seams. Without the sealants, water may flow between panel joints and into the insulation system below the metal panels. When metallic coatings begin to fail, the panel has reached the end of its service life. Metal roof systems capture roughly 9 percent of the low-slope roof market. Despite their high initial cost, a metal roof may be a good choice for a re-roof project. |