FM Approved Lap Seam Roofs

The Hazards

Roofing systems are the first line of defense in the complete building envelope that includes the roof, walls, windows, doors and flashing. Roofing systems must be able to protect a structure from the natural hazards associated with the local environment, including rain, hail, snow, high winds, temperature extremes, and even fire.

Metal roofing has been used for hundreds of years on structures around the world. When manufactured, specified and installed correctly, standing seam and lap seam metal roofs provide an attractive, long lasting, lightweight, and easily recyclable alter- native to other types of roof coverings including single plies, and asphalt or built-up roofing. Many metal roofing systems come with warranties of up to 50 years.

Lap seam metal roofing systems typically consist of a 22-26 gauge corrugated or flat metal panel that is formed in a factory or on site and installed, with or without insulation batts, directly to structural purlins. The edges and ends of overlapping metal roofing panels are sealed with a butyl adhesive tape or other sealants. Color-matching screws with a rubber or EPDM washers are driven through the panels directly into the underlying purlins.

Wind uplift resistance, combustibility, moisture resistance, durability, quality and manufacturing consistency are just some of the factors to consider when specifying lap seam metal roofing systems. Most lap seam metal roof panels are formed from steel. However, this type of roof system also may be available in aluminum or copper.

Testing Required for FM Approval

FM Approvals is a leader in certification and Approval of roofing products and roof assemblies. FM Approval is based on performance testing of completed assemblies when subjected to multiple perils. A typical FM Approvals program includes fire testing above and below the deck, wind-uplift testing, and hail-damageability testing.

FM Approved roofing products and assemblies are listed in RoofNav (www.roofnav.com), FM Approval’s online tool for roofing professionals. RoofNav takes the guesswork out of configuring an FM Approved roofing system by putting all roofing-related information, including related installation recommendations from relevant FM Global Property Loss Prevention Data Sheets in one place.

 Lap seam metal roofing systems are evaluated under Approval Standard 4471, Class 1 Panel Roofs, which includes performance requirements for:

• Combustibility above and below the roof assembly
• Wind uplift resistance
• Foot traffic resistance
• Hail damage resistance

A key test that sets FM Approval testing apart from other certification organizations is the full-scale 12 x 24 ft (3.7 x 7.3 m) wind uplift test. This full-scale test sample has been determined through years of testing and insurance loss experience to offer an accurate view of expected real-world performance. Typical design guides may be based on only one performance characteristic, such as panel pull over from the screw heads. Performance such as screw pull out or screw fracture may be ignored. Typical real-world failures have been documented and include any one or combination of the three possibilities listed above. The FM Approval test takes into consideration all three modes of potential failure.

To conduct this test, a complete roofing assembly is constructed in the FM Approvals laboratories at the FM Global Research Campus in West Glocester, R.I., USA. In the case of lap seam metal roofing, this would typically include the metal roofing panels, fasteners, EPDM washer, seam sealant, vinyl-backed batt insulation (if called for), affixed to metal purlins.

In addition, as with all FM Approval standards, Standard 4471 requires certain operations requirements be met, including: demonstration of a quality control program, initial and follow-up audits of manufacturing facilities and any field fabrication locations. Audits, in some cases, may be unannounced and conducted at least annually and more frequently, if necessary.

Benefits and Availability

Why choose an FM Approved roof assembly versus a non-certified product or design? An FM Approved roof means you get a tested roof system not simply a collection of products and parts that may or may not perform as expected. Through FM Approved products, you get a roofing system that has been proven in extensive testing to perform as specified, including wind uplift, fire resistance and many other factors.

With an FM Approved roofing system, you are assured that the manufacturers of the components that make up that system have proven quality programs in place, both in their factories and on the job site. For building owners and investors, when you demand an FM Approved roof assembly for your project, you are more than simply meeting basic code requirements you are ensuring that the most important building envelope component will protect your structure for many years to come.

But What About…

Cost? It is important to understand the product manufacturer’s pricing structure.

It may appear that the cost of a tested and certified FM Approved lap seam roofing system is more than that of a comparable, non-certified system. Reputable testing and certification organizations such as FM Approvals will run tests and perform facility audits, which may, in fact, increase the cost of the product compared to similar, non-certified products, but not always.

The best place to start any pricing comparison is the manufacturer’s website. Very often, pricing sheets are available, or at least a link to a representative who can explain the actual cost that a manufacturer is charging his customers.

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