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.


January 22, 2020
Wood Nailers for Roofing

Wood nailers are often overlooked, but they are a very important component of a successful roof assembly. A horizontal wood nailer is used to provide an effective substrate for some installation details and for other roof accessories. In addition, it is used to provide solid protection for the edge of the membrane underlayment. At a minimum, wood nailers must be thick enough that the top of the nailer is flush with the top of the membrane underlayment. General Criteria: The width of the nailers must exceed the width of the metal flange of edgings, scuppers, etc. When treated lumber is specified, it is recommended that only lumber that has been pressure treated with salt preservatives be specified. Lumber treated with any of the wood preservatives such as, Creosote, Pentachlorophenol, Copper Naphthenate, and Copper 8-quinolinolate will adversely affect the membrane when in direct contact and are, therefore, unacceptable. If non-treated lumber is to be specified, it must be stored to protect from moisture sources. A seal should be provided between the non-treated lumber and a concrete or gypsum substrate. Methods used to fasten the nailer vary with building conditions; however, it is essential that secure attachment of durable stock be accomplished. Factory Mutual Loss Prevention Data Bulletin 1-49 (Perimeter Flashing) contains options for the spacing and sizing of fasteners based on the project wind zone. Wood nailers that are anchored to steel, wood, or masonry decking should not be less than 2" x 6" nominal (minimum 1-1/2" x 5-1/2"). Wood nailers should be Douglas Fir, Southern Yellow Pine, or of wood having similar decay-resistant properties. The American Wood Protection Association (AWPA) publishes the AWPA Book of Standards and is the industry standard for wood treatment. U1 is the specification for treated wood and outlines wood species, preservatives, and specifications for their Use Category System. This is a great resource when you have questions of when and where you should treat wood and what are the recommendations for various treatments. Carlisle SynTec publishes some topics in the Design References portion of our product binder, which can also be accessed on the Carlisle SynTec website. For more information on wood nailer attachment, including some drawings, click here. Contact Craig Tyler at [email protected] with further questions.

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January 8, 2020
Air and Vapor Barriers for Roofs

In 2012, the International Energy Conservation Code (IECC) introduced the continuous air barrier requirement for new commercial construction. This meant that air and vapor barriers were now required for walls, and they must be tied to both the roofing assembly and the foundation. For years, many architects and designers only utilized an air and vapor barrier on the roof deck for high-humidity occupancies, such as swimming pools or food processing facilities. But the new requirement meant taking a hard look at the needs of all buildings and what a roof assembly could do for the building envelope. A single-ply membrane, as stated in the IECC and as tested utilizing the ASTM E2178 standard, qualifies as an air barrier and can satisfy the requirement for an air barrier on any given project. So why would you consider adding an additional air and vapor barrier to the roofing assembly? There are a couple of very simple reasons: Reason 1: Air Intrusion. While a properly installed roofing system will not allow air leakage (e.g., conditioned indoor air from exiting the building thermal envelope), it does allow air movement within the roof assembly. As the single-ply roof membrane is on the top of the assembly, indoor conditioned air can infiltrate into the roofing system and travel into the layers of insulation or cover boards. Why is this an issue? See Reason 2… Reason 2: Moisture Migration. Adding a deck-level air and vapor barrier is a great solution to prevent air intrusion and moisture migration. This also allows the wall air and vapor barrier to be tied together at the deck level, which allows the roof to be replaced more easily in the future. The contractor will not be modifying the continuous air barrier when re-roofing, as the roof is no longer that barrier. Carlisle SynTec provides many options for deck level air and vapor barriers: VapAir Seal MD for steel deck construction, direct to deck; VapAir Seal 725TR for Concrete Decks; VapAir Seal Flashing Foam for sealing around penetrations such as pipes; Go to the Air and Vapor Barriers Product Page on the Carlisle SynTec website for more information, specifications, and details. Contact Craig Tyler at [email protected] with further questions.

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December 18, 2019
Cold Weather Installation Tips Part 2 - Membranes and Insulation

As discussed in the previous SpecTopic, "Cold Weather Installation Tips Part 1 - Low-VOC Bonding Adhesives and Primers", specifying and handling of building envelope products is challenging during the colder winter months. Single-ply membranes and rigid insulation boards need some extra consideration, as they can be adversely affected by outside temperatures. For starters, all membranes will need time to "relax" after being unrolled from the original packaging; this applies to EPDM, TPO, PVC and KEE HP. It is also suggested that membrane widths be limited to a maximum of 10 feet for adhered roofing systems. Treat flashing products and accessories as you would adhesives and primers, by utilizing heated storage enclosures or "hot boxes". This practice is strongly recommended when ambient temperatures are expected to fall below 40°F for an extended period of time. In all applications, but especially in cold conditions, insulation and underlayments must be stored so that they are kept dry and protected from the elements. Insulations should be stored on a skid, covered with a breathable tarp, and weighted to prevent wind damage. In winter months, ice and frost can form on the membrane. This can be difficult to see and can remain on the roof well into the day, especially on white membranes. This can be especially hazardous when working near the edge of the roof. Additionally, frost on metal edges and copings can create a very slick surface and cause ladders to slide and shift. Never step onto a metal coping when it is frost- or snow-covered. So for your next cold weather specification for single-ply membranes and rigid board insulation, include some installation precautions as mentioned. Contact Craig Tyler at [email protected] with further questions.

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