All Things Gypsum: Cooler Nails
The Gypsum Association is, assuming that document processing has proceeded on schedule since this column was written, on the cusp of releasing the latest edition of the Fire Resistance Design Manual, GA-600. We anticipate a late spring publication of the 2012 document.
While we believe GA-600 to be the paramount resource for gypsum board fire and sound test information, the Gypsum Association staff is fully cognizant of, and recognizes the presence of, numerous fire and sound test listings that exist in other resource documents. One example of an additional resource is the “Prescriptive Fire Resistance” tables in Chapter 7 of the International Building Code. The Chapter 7 tables are very popular in areas where the Uniform Building Code was historically enforced, primarily states in the western U.S., and were integrated into the IBC during the 2000 model code consolidation process.
THINGS (DON’T ALWAYS) CHANGE
As useful as the tables are, and they are an excellent resource, they display a bit of an innate flaw. Unlike GA-600, which gets a thorough cleansing every three years, antiquated language can remain in the tables unless a code change proposal is submitted to remove or modify the text. Given the breadth and density of the information in the tables, a wholesale modification can be daunting.
Therefore, the tables contain intermittent references to outdated materials and techniques. An example is the occasional mandate requiring the use of cooler nails for the attachment of gypsum board. Cooler nails have largely been replaced by drywall nails and are not often used to attach gypsum board in contemporary construction. The references to cooler nails are outdated and create confusion.
NOT JUST FOR THE FRIDGE ANYMORE
Cooler nails were designed for use in building pallets and crates for the storage and transport of food and vegetables. Their name reflects their use in building “coolers” for refrigerated and frozen produce. A cooler nail is similar in profile to a common nail, but has a thinner shank and slightly tapered head to prevent splitting the thin pieces of wood used to construct crates. They work well for the application of gypsum board because the thin shank-often 20 to 25 percent thinner than that of a similar length common nail-creates a significant surface area to the underside of the nail head. In fire rated systems, it is the surface area of the underside of the head that is important in terms of a fastener’s ability to support the gypsum board. The thick head of a common nail can also tear the face paper of a board, whereas the tapered head of a cooler or drywall nail will set below the surface of the paper without tearing it.
When confronted by a system that requires the use of cooler nails for test compliance, the most obvious option is to obtain cooler nails to attach the board. Cooler nails are available and can be purchased online in bulk quantities. However, it is hard to find them in the standard 4d (1⅜-inch) and 6d (1⅞-inch) lengths most often used for gypsum board attachment-readily available cooler nails tend to be at least a 7d (2⅛-inch) minimum length-and they aren’t always stocked by big-box retailers or drywall yards.
If you can’t find cooler nails, or don’t want the hassles involved in finding them, another option is to substitute a screw having the same or greater dimensions than the prescribed cooler nail on a one-to-one basis. This is a common practice and is permitted by GA-600 and the Underwriter Laboratories “Online Certifications Directory.”
GA-600 permits the substitution of “screws meeting ASTM C 1002 for the prescribed nails, one for one, when the length and head diameter of the screws equal or exceed those of the nails specified in the tested system.” To comply with the C 1002 standard, the major width dimension of the shank of a gypsum board screw must not be less than 0.136 inches, a dimension greater than the shank dimension of virtually every comparable length drywall or cooler nail. The head of a C 1002 drywall screw is also larger than that of a cooler nail.
In general, you shouldn’t have any problems making the substitution; however, a drawback can be the length of the fastener described in the test. If the system requires a 6d nail, you must use a 1⅞-inch-long screw to comply with the substitution requirement. That’s a long screw for a single-layer application.
If you are attempting to make the substitution for a system in Table 721 of the IBC, language addressing the screw substitution is contained in an ICC-ES Evaluation Report ESR-1338 that is sponsored by the Gypsum Association. Copies of the report can be downloaded from www.gypsum.org.
You can also search for a fire test that is identical to the original test, except for the fasteners used and the spacing of the fasteners. Many nail-applied fire tests have virtually identical screw-applied versions that permit the use of fewer screws and incorporate screws that are shorter than the nails used in the nail-applied versions.
Substituting a drywall nail of comparable length for the cooler nail is also an option. In some instances, it is an easy substitution as some of the systems in the IBC permit the use of either a “cooler or drywall nail.” The drywall nail must comply with the size mandates for the system and must be manufactured in accordance with one of the standards listed in the code: C 514, F 547, or F 1667.
In other instances, it can be a more difficult substitution process. The IBC doesn’t contain language allowing a direct substitution of a nail for a nail, and no language similar to the screw language exists in the ESR-1338 report. So, the path can be a bit bumpier, and you may need to be a gentle persuader to get your way.
Fortunately, both GA-600 and the UL Directory blaze a bit of a path in this instance. Language in the General Explanatory notes section of GA-600: 1) requires nails for the systems in the manual to comply with ASTM F 547 or ASTM C 514 and 2) permits “other nails, suitable for the intended use, and having dimensions not less than those specified in this Manual shall be permitted as substitutions.” With this logic, you generally are safe using a C 514 nail in a rated system as long you comply with the dimensional size minimum language and abide by the spacing requirements described in the tested system description. In nearly every instance, the shank dimensions of identical length cooler and drywall nails are virtually identical and the head of a typical drywall nail is at least as large as, if not slightly larger than, the head of a comparable length cooler nail.
JUST DON’T GO CHEAP
Note the importance in both instances of following the fastener application pattern described in the system. You can’t try to use fewer fasteners by installing fasteners that are longer than those described in the system description. The use of a reduced quantity of fasteners overall will compromise the overall fire-resistive integrity of the system.
Cooler nail language has become much less frequent in fire-tests with the passage of time as most contemporary tests are conducted using standard drywall nails. However, it does appear on occasion in older tests and tests conducted on proprietary materials. As always, if you are making a swap based on the logic outlined in any of the methods described herein, make sure you get the approval of the authorities having jurisdiction over the project before you make the change.