Effective Fasteners for Metal Roof Construction

SELF-TAP TO SELF-DRILL

Before the mid-1960s, if you were looking for the most effective fastener screw for your metal roof, you probably found a self-tapping fastener (A, AB, B). Today, there are still installers trained on self-tapping fasteners who consider them to be the most effective way to attach panels.

Self-tapping fasteners usually have a 14-diameter hex- or hex-washer head, and feature steel-backed, bonded rubber washers. A washer assembly not attached to the screw moves to accommodate any error in driving the screw. “If the fastener is driven a few degrees off vertical (to the panel), the washer can move to provide a seal,” says David Webster, Leland Industries, Toronto. “Self-tapping fasteners require drilling pilot holes in the panel and structural material, a time-consuming step. The additional labor may negate any savings when using self-tapping fasteners in preference to self-drilling fasteners. Self-tapping fasteners are more likely to be supplied with mechanical zinc plating, [which is] a thicker plating. This is considered obsolescent by some, but is still routinely applied to certain self-tapping fasteners.”

Modern self-drilling fasteners come in a much greater variety and many find them more effective for metal construction applications and profiles. Webster says fastener diameters #8, #10, #12 and #14 are the most commonly used and most effective with lengths from 1/4-inch to 8 inches. There are at least eight different head style types, the most common being some form of hex washer head in 1/4-inch, 3/8-inch or 7/16-inch diameter.

Webster cites an advantage, often overlooked with self-drilling fasteners, which is the hole size. “The size of the hole is the shank diameter, an important advantage when sealing the hole made by the drilling action,” he says. “Choice of shank diameter and head style allows for many fastening options. [There’s] a choice of head styles including low-profile heads for use with hidden fastener panels. I believe the best all-around fastener for attachment of metal sidewall or roofing panels will be a #12 diameter self-drilling screw with a point capable of drilling through multiple laps of high-tensile sheet and the structural member. The screw must penetrate the member to show a minimum three laps of thread when seated. This will ensure that fully crested threads are engaged to provide maximum holding power. The #12 fastener will feature a hex washer head with a washer face to bear on the accessory sealing washer. The washer drives straight but allows movement if the screw is driven off the vertical.”

SUBSTRATE CONSIDERATION

The type of metal panel being fastened largely determines the most effective fastener. For instance, “Installing an R-Panel into wood using a #10 Pole Barn Fastener with a Hi-Lo thread will provide better pull-out values and if the fastener has a type-17 point then that allows for quicker/easier drilling,” says Ken Webb, Dynamic Fastener, Kansas City, Mo.

For metal-to-metal applications, choosing the most appropriate fastener often starts with determining the total thickness of the material being fastened. “Attaching roofing sheets to a purlin, the #12 with a T-3 self-drilling point has a drilling capability from 0.036-inch to 0.210-inch total steel thickness,” Webb says. “For roof lap stitching, a 14-14 x 7/8-inch T-1 can be used. The T-1 has a mini drill point that can attach total steel thickness of 0.024-inch to 0.095-inch. To attach roofing sheets to structural steel, Dynamic Fastener offers a T-5 Fenderhead that can drill from 0.250-inch to 0.625-inch total steel thickness.”

COATINGS AND CAPS

Self-drilling fasteners come in many forms: zinc-coated, zinc aluminum cap or molded head fasteners, stainless capped screws, and even bi-metal stainless screws with carbon-steel drill points.

Generally, the most effective fastener screws are those capped with a non-corrosive metal or alloy to provide the longest life. Stainless steel bi-metal screws need to be used when attaching two dissimilar metals such as steel and aluminum.

“Fasteners that drill or pierce the metal panel from the topside of the roof and attach to the deck structure must have sealing washers made of EPDM to seal water from entering the building,” says Joe Stager, vice president of Triangle Fastener Corp., Pittsburgh. “Because the head of the screw is exposed to weather, they should be plated or coated with a finish that provides increased corrosion resistance than ordinary zinc-plated fastener screws at a minimum.”

When attaching hidden fastener panels for applications like standing seam roofing, pancake head fasteners are often the most effective. “These fasteners are designed to be protected from the elements and are usually not coated with as thick a coating of zinc,” says Tim Martin, regional sales manager, Levi’s Building Components, Leola, Pa. “Stainless steel versions are also available. These fasteners are covered by the next panel and are hidden from view. The heads on these fasteners are very thin and should not telegraph through the panel.”

Alan Belcher, branch manager at Triangle Fastener’s Jacksonville, Fla., location, says #10 low-profile pancake head fasteners are effective for clipless or nail-hem panels. Clipless panels fasten directly to the roof deck. “The low-profile head is less likely to dimple the panel covering the fastened side of preceding panel when installed,” he says. “A wafer head is even better, but the tapered shoulder can impact the panel negatively as well.”

EFFECTIVE SELECTION HELP

This is just a brief overview of some of the most effective fasteners for metal construction. More detailed and thorough information is available. Stager says associations like Metal Construction Association publish documents on fastener selection. Fastener suppliers are usually the first stop for help. Dynamic Fastener has a 2020 Tool and Fastener Hand Guide to assist customers. Belcher says Triangle has an app for smartphones on his company’s website for help.

“Most fastener suppliers have catalogs and websites that detail the testing done on the fasteners, warranties and other technical information about the screws available,” says Martin. “Certainly, fastener companies who offer a diverse array of application-specific fasteners and back it up with a high level of product and application knowledge, can be a great resource for fastener purchasers,” agrees Chris Ray, national sales manager for Levi’s Building Components.

Leland advises attending trade shows and open houses where exhibitors lay out large quantities of sales literature. “Pick it up, take it home and read,” he says. “Sales literature contains much of what you need to know about the product. Talk with a sales representative. Request a demonstration. Reputable manufacturers can usually accommodate a job-site visit to show how the product performs. New products are on display at trade shows, and often the manufacturer is on hand with short seminars and videos to show the product at work. Go online, it’s amazing how much information is available from the manufacturer.”

Ray urges fastener customers to always consider the options and review the advantages and disadvantages of each fastener, taking into account factors such as quality and versatility as they relate to the specific job. “Each application is unique,” he adds. “Making the right fastener selection at the outset will ensure end-user satisfaction and product performance, and eliminate problems down the road.”