FM 1-90 vs. ASCE 7
May 15, 2019
Wind uplift design for roofing can seem daunting to the uninitiated. But with a little help from online tools, it can be much more straightforward. Wind uplift is calculated for all buildings using formulas, tables, and wind maps developed by the American Society of Civil Engineers (ASCE) in their publication ASCE 7-2016. With a project’s location, building use/occupancy, building height, and roof plan, there are a number of online tools you can use to determine the wind uplift required for your building. The calculator used by the National Roofing Contractors Association (NRCA) can be found at http://www.roofwinddesigner.com/.

Once the uplift pressures for your building are determined, you must choose a design for your building that meets these pressures. Roofing manufacturers list their system designs through the DORA Directory of Roof Assemblies https://www.dora-directory.com/ or through Factory Mutual Global’s RoofNav® https://www.roofnav.com/Account/Login.

The DORA Directory lists roofing assemblies based on uplift testing that various manufacturers have received through third-party verification, while FM’s RoofNav lists roofing assemblies that have been tested through FM Global’s own testing facility.

Roofing assemblies that meet the minimum uplift requirements per ASCE 7-16 will meet the International Building Code (IBC); however, FM Global ratings may require additional enhancements based on their own calculations. The more stringent guidelines are due to the fact that FM Global is an insurance company and they approve designs before they issue coverage for a particular building.

While FM 1-90 is a rating used by FM Global-insured buildings as a standard for their insurance coverage, the calculation of wind load for a particular building using ASCE 7 calculations is the basis for designing a roof meeting the IBC for all buildings, whether or not they are insured by FM Global.

Meeting the standard for FM 1-90 will result in higher pressures in the perimeter and corners than using the ASCE 7 method, thereby increasing the cost of the construction of the roof. Changing these requirements at a later date or finding out your project does not require FM ratings may cause confusion during the bidding process and could result in higher bids.

Always verify your need for FM Global before proceeding with wind load design. Contact Craig Tyler at [email protected] with questions.


September 18, 2019
Fire Performance of Polyiso

All construction materials, including foam plastics such as polyiso insulation, must provide a suitable margin of fire safety. Polyiso possesses a high level of inherent fire resistance when compared to other foam plastic insulations due to its unique structure of strong isocyanurate chemical bonds. These bonds result in improved high-temperature resistance (up to 390°F [199°C], more than twice that of other building insulation foams) which in turn leads to enhanced fire resistance. In addition, because polyiso does not melt or drip when exposed to flame, but rather forms a protective surface char, its fire resistance is further enhanced, especially in terms of flame spread and flashover potential. Polyiso passes both the ANSI UL 1256 and FM 4450 fire tests without a thermal barrier. Polyiso, a thermoset material, stays intact during fire exposure in the ASTM E84 or "Tunnel Test.” It forms a protective char layer and remains in place during the test, thereby meeting all building code requirements and contributing to a fire-safe building. For more information on polyiso’s performance in fire tests, visit the 'Technical Bulletins’ page on the PIMA (Polyiso Manufacturers Association) Website where you can find the following papers: Technical Bulletin 103: Fire Performance in Walls and Ceilings Discusses polyiso insulation as it relates to building codes in construction and fire tests in walls and ceilings, including ASTM E84 and ASTM E119. Technical Bulletin 104: Fire Performance in Roof Systems Provides an overview of polyiso insulation requirements for roof systems and key issues in fire performance, including the importance of the FM 4450 Calorimeter Tests and the UL 1256 Resistance to Interior Spread of Flame test. Technical Bulletin 105: Fire Test Definitions Provides an in-depth look at fire test procedures for building applications. Technical Bulletin 111: Class A and Class 1 Roof Assemblies Are Not the Same Explains why Class 1 and Class A are not the same. Technical Bulletin 111C: Roofing Regulations in Canada – Class A and Class 1 Roof Assemblies Are Not the Same Explains why Class 1 and Class A are not the same. Technical Bulletin 405: Fire Resistance Properties of Polyiso Foam Plastic Insulation Used in Wall Assemblies – Facts and Comparisons Looks at the minimum fire resistance properties required for foam plastic insulation and compares data on polyiso with other recognized combustible materials. Product Stewardship Paper 100: Polyiso Insulation and Flame Retardants New Product Stewardship report on polyiso and flame retardants. Contact Craig Tyler at [email protected] with questions.

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September 4, 2019
Alternative Uses for Roofing Membranes

All single-ply membranes make for great roofing systems, but they can be used for a variety of other purposes too. EPDM, TPO, and PVC can be used in the lining of underground tunnels and can serve as liners for water retention ponds, irrigation canals, and other water containment systems. For years, EPDM membranes were used as pond liners – even before they were utilized for commercial roofing. You could see EPDM pond liners being used in agriculture for irrigation canals and ditches, by municipal water systems for retention ponds and spillways, and even in backyards as small ponds and water features. This is still true today, and EPDM has expanded into additional markets such as tunnel waterproofing. The number of large underground transportation tunnels used for vehicle traffic or metropolitan railways has certainly increased in the last few decades as traffic and access needs continue to outstrip the supply of existing infrastructure. These tunnels have to keep water out, whether they’re underneath a river or traversing through a mountain, and single-ply membranes meet their waterproofing needs with the same technology used on the roof. Different types of membrane offer specific benefits, from EPDM’s large sheet size to thermoplastics’ (TPO/PVC) seam weldability. Regardless of whether the tunnel is a boring project or a “cut and cover”, lining the tunnel can be accomplished using several different installation methods and can utilize EPDM, TPO, or PVC. For more information, please consult the links for the products or specifications on the Carlisle SynTec website below. Tunnels – Conventional Blindside Method Consult the Tunnel Waterproofing System – Conventional Specification and Details on the Carlisle SynTec website.  Tunnels – Cut and Cover Method Consult the Tunnel Waterproofing System – Cut and Cover Specification and Details on the Carlisle SynTec website.  Pond Liners Consult GeoMembrane Page for Pond Liner Products and Brochures on the Carlisle SynTec website.   Contact Craig Tyler at [email protected] with questions.

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August 21, 2019
Understanding FM 1-52

There are two recognized field test methods for determining uplift resistance of adhered membrane roof systems, both of which can be problematic: ASTM E907, "Standard Test Method for Field Testing Uplift Resistance of Adhered Membrane Roofing Systems," and  FM Global Loss Prevention Data Sheet 1-52 (FM 1-52), "Field Verification of Roof Wind Uplift Resistance."  Both test methods provide for affixing a 5’ x 5’ dome-like chamber to the roof’s surface and applying a defined negative (uplift) pressure inside the chamber to the roof system's exterior-side surface using a vacuum pump, like in the photo below.  An example of a test chamber used for negative-pressure uplift testing However, ASTM E907 and FM 1-52 differ notably in their test cycles and maximum test pressures for determining roof system deflections and whether a roof system passes or is “suspect”. Using ASTM E907, a roof system is “suspect” if the deflection measured during the test is 25 mm (about 1 inch) or greater.  Using FM 1-52, a roof system is “suspect” if the measured deflection is between ¼ of an inch and 15/16 of an inch, depending on the maximum test pressure; 1 inch where a thin cover board is used; or 2 inches where a thin cover board or flexible, mechanically attached insulation is used.  Test results' reliability  The reliability of the results derived from ASTM E907 and FM 1-52 is a concern, especially when the tests are used for quality assurance purposes. A note in ASTM E907 acknowledges its test viability. "Deflection due to negative pressure will potentially vary at different locations because of varying stiffness of the roof system assembly. Stiffness of a roof system assembly, including the deck, is influenced by the location of mechanical fasteners, thickness of insulation, stiffness of deck, and by the type, proximity, and rigidity of connections between the deck and framing system." For example, when testing an adhered roof system over a steel roof deck, placement of the test chamber relative to the deck supports (bar joists) can have a significant effect on the test results. If positioned between deck supports, the test chamber's deflection gauge will measure roof assembly deflection at the deck's midspan, which is the point of maximum deck deflection. Also, in many instances, field-uplift testing results in steel roof deck overstress and deck deflections far in excess of design values, which can result in roof system failure. These situations can result in false “suspect” determinations of a roof system. Industry position/recommendations Because of the known variability in test results using ASTM E907 and FM 1-52 and the lack of correlation between laboratory uplift-resistance testing and field-uplift testing, the roofing industry considers field-uplift testing to be inappropriate for use as a post-installation quality-assurance measure for membrane roof systems. Conclusion FM 1-52 is an FM Global-promulgated evaluation method and not a recognized industry-consensus test standard. The scope of FM 1-52 indicates that it’s only intended to confirm acceptable wind-uplift resistance on completed roof systems in hurricane-prone regions, where a partial blow-off has occurred, or where inferior roof system construction is suspected or known to be present. FM 1-52 was originally published by FM Global in October 1970. The negative-pressure uplift test was added in August 1980 and has been revised several times. The current edition is dated July 2012 and includes an option for "visual construction observation (VCO)" as an alternative to negative-pressure uplift testing. VCO provides for full-time, third-party monitoring to verify roof system installation is in accordance with contract documents. For more information, contact Craig Tyler.

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