By Brian Farrell
As important as knowing the differences in metal roofing products, it is more important to know the differences in the fasteners holding that roof in place. There seems to be a lack of knowledge about fasteners, not only among metal panel and metal building suppliers but also among the contracting community. It is extremely important to choose the proper fastener for the proper application so here are some things to consider…
Fasteners are described by their size based upon the major thread diameter, threads per inch, length, head style and type of drill point. It sounds complicated but broken down into its parts simplifies everything. The diameter is a numerical value used to describe thread diameter. A #12 diameter, the most common, has roughly 7/32” diameter threads. This is no different than visiting your local hardware store and choosing a screw that is a #6 or a #8. The higher the number, the larger the diameter.
The next item, threads per inch describes exactly that, how many threads are there in a one inch length of the screw. The threads per inch will vary based upon the material for which the screw is designed A screw designed for thinner material such as 26 gauge, will have less threads per inch than a screw designed for ¼” steel. The threads per inch will also dictate the pull-out strength.
The length is an easy one. It indicates the length of the fastener body, not including the head. Choosing the proper length is critical with the implementation of the new energy codes and the increased thicknesses and types of insulation. As an example, a screw with a length of 1-1/4” will not work well with 6” of fiberglass insulation.
The head style is indicated by several different descriptions; however, the vast majority of metal building fasteners are HWH or Hex Washer Head. This does not indicate that the fastener has a washer since there can HWH with a washer or HWH without a washer. It only indicates the type of head. Most HWH fasteners used in metal buildings are either a 5/16” or a 3/8” diameter head.
The last number indicates the type of drill point. Drill points are generally designated as #1, #2, #3, #4, #4.5 or #5. Don’t let this be confusing. The drill point denotes the metal thickness for which the fastener was designed. The majority of structural metal building fasteners are a #3 which means they were designed to drill through .036 or 20 gauge up to .210 or a little less than ¼” in thickness. A fastener with a drill point of #4, #4.5, or #5 is designed for heavier gauge steel and will be discussed below.
Using all of this information, a fastener described as a 12-14 x 1/1/2 HWH 3 has a screw size of 12 or roughly 7/32” diameter, 14 threads per inch, is 1-1/2” long as measured from under the head to the tip of the drill point, has a hex washer head without a sealing washer, and a #3 drill point. It is basically a standard metal building fastener used to fasten panel to the secondary members.
You may be asking yourself…does all this matter? In order to choose the proper fastener, you need to know fastener basics.
Back to the drill points. Trying to fasten a part through ¼” plate or the chord of a bar joist with a fastener that has #3 drill point will be a time-consuming and frustrating process. The standard metal building fastener is not made for this application; however, all manufacturers offer a 12-24 fastener for this specific application. The drill point is a #4, #4.5, or #5, and the threads are closely spaced together, 24 per inch, for ease of drilling and securing.
The second most common metal building fastener is a lap or stitch fastener normally described as a 12-14 x 3/4”, 1/4-14 x 7/8” or the latest which is 1/4-10 x1”. As indicated by the description, the first two are the same diameter as the previously-described structural fastener; however, they are less than 1” in length with a #1 drill point made to penetrate only light-gauge steel. The 1/4-10 x 1 is a fairly recent addition to the stitch screw family having only 10 threads per inch, thus in theory should pull the two materials together tighter than a screw with #14 diameter thread. These stitch fasteners are rated for material thicknesses of .018 (26 gauge) through .095 (12 gauge) but realistically, use them only for connecting light-gauge material together.
Lastly, there is a 1/4-14 x1-1/8 stitch fastener originally developed for the lap condition of a trapezoidal standing seam roof. The design of this screw allows it to drill through the two lapped panels as well as the panel stiffener and then tightly draw all three together. It virtually eliminated the issue of a fastener drilling through the lapped panels and pushing the stiffener down instead of drilling through it and tightly pulling all the layers together.
Although the HWH or hex washer head configuration is the most popular, there are several applications where its use is not feasible such as using it to fasten certain standing seam clips or to fasten the cleats for cleated trim conditions. Where head clearance is an issue, the same type structural fastener can be obtained with a “pancake” head, which is a low-profile Phillips or square drive style head. These are not as easy to drill as a HWH but the application demands a low-profile head. There are a few applications, especially with certain architectural roofing profiles, where a pancake head is still too thick and head transference is an issue. Many manufacturers offer an ultra-low-profile pancake head with the same Philips or square drive but with a thinner head compensated by a bugle type configuration below the head.
Choose your fastener carefully as your roof and wall panel performance depend on it.
(The author would like to thank Marty Martin and Joe Stager of Triangle Fasteners for their assistance in proofing this article.)