Wide Span Metal Roofing - 7/10/2001 - Home Exterior Roofs Siding

Wide Span Metal Roofing

Improvements from old, labor-intensive metal roofing

Metal roofing products of old had two drawbacks – standing seams were field-formed and panel attachment was through the roof deck, requiring screws, washers, sealant, and subsequent maintenance of these points of penetration. The field forming (folding and crimping) of the standing seams between panels was a tedious process and labor accounted for more than 80% of the installed price of the roof covering.

Some of this labor-intensivity has been eliminated with new cold-rolled steel roofing products. Panel edges have been designed with snap locking standing seams to accommodate a concealed fastener that saves installation and maintenance labor while enhancing the appearance and durability of the roofing product. Various gauges and designs also provide a rigidity that allows panels to be installed without substrates (sheathing) on 3/12 or steeper sloped roofs with spacing of supports as great as 5’ on center.

The span capability of traditional roof substrates – 7/16" OSB and ˝" plywood – have played a part in typical roof truss design and spacing. But wood roof trusses in residential spans can be engineered for spacing wider than 2’ o.c. When a truss can be engineered as a one-ply member at wider spacing, usually by designing with a better grade or species of lumber or upsizing chord members, metal roofing products now available can bridge this distance up to 5’o.c.

Panels are preformed of 22-26 gauge steel and have a fluorocarbon coating applied in the factory. Finishes typically have a 20-year warranty, while the life expectancy of the steel panel is 40 or more years.

Panels are 18" – 28" in width and can be fabricated and transported in lengths up to 45’. Each panel is rolled with a male assembly along one edge and a female assembly along the opposite edge that create the standing seam when snapped into place. One side of the snap lock usually has a factory-applied sealant along the leading edge to prevent water penetration. Clips are applied to the male edge so that when the next panel is locked in place the clip is concealed and the interlocking pattern of the seam secures the adjacent panel. Optional battens can be installed atop the seam for added dimensional profile.

Wide span metal roofing remains more costly than conventional assemblies even when longer life cycle architectural shingles are specified. While there is clearly a savings in decreasing the quantity of trusses required and eliminating roof sheathing in an assembly, much of the economy is traded off for additional measures which must be taken to install 2’ o.c. ceiling drywall nailers and top chord purlins. Because most manufacturer’s panels are customized by length and color, wide spread distribution is limited and transportation costs contribute disproportionately to the cost of small quantities, like the 1400 sq. ft. required for the average home. Mobile rollers may provide the solution to this transportation/ cost issue on small jobs.

Wide span metal roofing brings the cost of standing seam metal roofing closer to conventional shingle roofing. Added benefits include appearance, fire resistance, and durability.

The Metal Roofing Alliance identifies the cost saving opportunities of greater energy efficiency, less frequent repair and replacement, and lower insurance costs (currently in Texas).

Provided that the manufacturer’s products have met the requirements of ASTM weatherization and impact resistance tests and UL wind uplift tests prescribed by the building codes, the wide span metal roofing assembly is permitted under the BOCA, CABO, SBC, and International Code.

Not Applicable

Trusses are installed and permanently braced with purlins as per the truss engineer’s and roofing material manufacturer’s specifications. The top chord permanent lateral bracing requirements and the fastener schedule of the metal roof panel are compared and the closest spacing requirement will be prescribed. To serve the multiple purposes of panel clip nailers and permanent lateral bracing, purlins are at least flat 2x4x12’ lumber double nailed to the truss top chord.

Most metal roofing panels layout vertically, while a few have a horizontal orientation. Some roof panels are ordered from the plant, and others are cold rolled using a mobile unit on site. The vertical panel’s length should be seamless along the roof’s run from peak to overhang edge. End cap, eave edge transitions, valley, and other specialty components are also available from manufacturers. For simple, gabled installations, roofers have had success ordering a 26 gauge or lighter coil roll and mechanically fashioning their own accessories on site using a siding or sheet metal brake.

Panels are placed and secured one at a time. However, installation techniques vary with type of concealed fastener used. While both gauge and panel design determine a product’s stiffness and strength, panel buckling can occur and care must be taken to properly place and secure each panel. Installers need to be experienced with the product. Oil canning, or apparent waviness in the finished plane, is an inherent characteristic of light gauge metal sheeting. Misalignment of panels, thermal expansion and overdriving of fasteners are some of the contributing factors.

"Most metal roofing comes with a true 30-50 year manufacturer warranty, plus a workmanship warranty from the installer." (Source: Metal Roofing Alliance)

Wide span metal roofing brings the cost of standing seam metal roofing closer to conventional shingle roofing. Added benefits include appearance, fire resistance, and durability.