Industry Focus >>Roofing Screws
屋頂螺絲概要
Although metal has been a material option for roofs
for hundreds of years, because of challenges posed byhigh cost, lousy appearance, and poor longevity, it has
only recently become a feasible mainstream choice. Infact, today in the United States metal roofing represents
one of the fastest growing areas in the residential roofing
segment. It is now possible to choose from a selectionof metal roofing solutions that either provide large,
continuous panels or metal alternatives to traditionalroofing materials such as slate, tiles, shakes, andshingles in attractive designs and at affordable prices.
Although some of these solutions are more expensivein the short-term than their traditional roofing options,
their superior durability and life expectancy makes
them a smarter long-term investment. Of course, likeany roofing material they must be securely fixed to theroofing substructure to protect the interior spaces below.
Since metal roofing solutions exhibit their own uniquequalities and challenges, many of these solutions require
special or different fasteners from nails and staples usedwith traditional roofing solutions. As metal roofing
has grown then, so has the need for innovation andengineering in the fasteners for this market space.
Figure 1: Metal Roof Made to Look Like a Tile Roof

Metal roofs can be classified into three distinct categories: Exposed Fastener Panel Type,Standing Seam Type, and Specialty Panel Type.
•Specialty Roofing Panels: These include both small and large metal panels thathave been fabricated to reproduce the look of ceramic tile, slate, shakes, and shingles(See Figure 1). Just like the items they are made to mimic, the panels are fastenedat their top and the attaching fasteners subsequently hidden by the next panel above.
These types of systems normally do not require specialty fasteners and often use thesame or similar fasteners to the ones utilized by the traditional products they replace.

•Standing Seam Systems: Standing Seam roofs are connected to the roof substrateby hidden clips. These clips are screwed to the substrate, often with special low
profile head screws, but without regard to special sealing because the screws arecovered with the roof panel and thus not vulnerable to water intrusion and exposure(See Figure 2). Panels are interlocked together at the seams. Metal roofs undergo
considerable expansion and contraction from changing heat and cold conditions.
Because a Standing Seam Roof essentially “f loats” over the roof substrate there
is no limitation in the length of the roof panel, and they often are seamless anduninterrupted. Standing seam roofs cost more to install but have a cleaner look and,more importantly, last longer.

•Exposed Fastener Systems: Exposed Fastener System roof panels are installed
directly into the roof understructure and are the most economical of all the metalroofing types (See Figure 3). The fasteners must be able to pierce the metal roofing
panel and self-tap into the supporting understructure.

•For this reason, there are different
versions for wood a nd met alconnections. Since the fasteners areexposed on the surface of the roof,
they must also have the capability
to seal the penetration f rom water
intrusion. The screws used in thismethod normally possess an externalhex f lange or washer head with abonded EPDM or Neoprene washer.
The heads and washers are usually
painted to match the color of theroofing panel. When properly installed
the washer is compressed to form atight seal around the roof penetration.
Since the panels are constrained by
the fasteners holding them down andthe metal panels undergo significant
ex pa nsion a nd cont r a ct ion w it htemperature changes, roof panels areusually limited to no longer than about
twenty-five feet (about eight meters)in length. Therefore, they may beoverlapped over long spans.

惠達雜誌Hardware & Fastener Components - no.62/2024◢ Metal Roofing101

Industry Focus >>◢ Roofing Materials

Today there are a variety of material choices. When properly
installed some of these materials are known to last a hundred yearsor more.
•Steel: Steel is the strongest and least expensive metal roofing
material. It is usually galvanized or coated with an AluminumZinc alloy called Galvalume and then painted. Steel roofing
panels will generally last 30 to 50 years.

•Aluminum: Aluminum is lighter, softer, and more expensive
than steel but will withstand the elements better than steel,
especially in areas of salt air or acid rain. Aluminum roofing
panels are almost always painted and will last 30 to 50 years.

•Copper: Copper is the longest lasting, most expensive, andperhaps most attractive of the metal roofing material choices.
Copper forms a natural patina over time and copper roofs havebeen known to last up to 200 years.

•Terre: Terre used to refer to a roof made of tin with a lead coating.
Today it is stainless steel that is sandwiched between layers of tin.
It does not hold paint but can last more than one hundred years.

•Zinc: Zinc is often alloyed with Titanium for added strengthand corrosion. It will last 80 to 100 years.

Figure 2: Example of a Standing Seam RoofFigure 3: Installation of Exposed Fastener Metal Roof System◢ Challenges

Hardware & Fastener Components - no.62/2024

Although all three metal roof types exhibit application
challenges, the exposed fastener system exhibits the greatest
challenge related to the fasteners. Thus, purchasers of thesesystems must wrestle with the question of whether the added costfor premium longer lasting solutions is justified while installers
must be very careful and intentional about how they install thefasteners that are specified. To perform properly, some of thefastener challenges that must be overcome with exposed fastenersystems are:102•

Condition of the Seal: The screw must be able to cleanly penetrate the metal panel and generate an effective and long-lasting seal.
Screws that are installed off-angle, under tightened, or over tightened may upon installation or over time begin to leak. Thus, a
successful roof seal is not only a function of how well the installer seats the screw but often also a function of the screw design, qualityof manufacture, and type of sealing element.

•Sealing Material: Sealing washers come in two varieties and two different materials, bonded
Figure 4: Example of Bonded
Dealing Washer
and non-bonded washers and EPDM (Ethylene Propylene Diene Monomer) and Neoprenematerials. A bonded washer is one where the rubber gasketing material is bonded (adhered) to thebottom of a slightly beveled metal washer (See Figure 4). The ID and OD of the rubber gasket
are slightly smaller than those of the metal washer it is attached to. This provides an overhang at
the outer edge protecting the gasket from UV rays and a small amount of interference from theID to retain the washer to the screw and to guarantee a tight seal around the screw itself. During
installation, the bevel in the metal washer flattens providing an even stress distribution acrossthe surface of the rubber washer. This prevents the screw head from embedding into the washer
and squeezing out at its periphery. This is particularly advantageous because when overtightened
the rubber gasketing material will want to creep away from the ensuing stress concentration which contributes to loss of clamp loadand sealing capability. Bonded washers can also be larger in diameter because the metal washer is able to distribute pressure over its
entire area. This provides a greater sealing area and makes it harder for water to penetrate the roof panel. Non-bonded washers arelimited in diameter by the size of the bearing diameter of the hex flange or washer head or, when utilized, a head cap. Both EPDMand Neoprene are good choices for roof sealing, although EPDM is considered superior since it has better heat, light, and ozone
resistance than Neoprene.

•Embrittlement of the Sealing Material: One of the challenges of using Neoprene and EPDM sealing material is vulnerability toenvironmental exposure. These materials are susceptible to temperature changes and get stiffer in the cold and creep in the heat.

惠達雜誌Industry Focus >>Prolonged exposure to such temperat ure cycles
eventually weakens the gasketing material. Worsethan the temperature cycling, however, is the exposure
to UV radiation. These materials are embrittled byUV rays so that the unprotected periphery that is
exposed ultimately breaks down and potentially opens
pathways for water intrusion.

•Damage to Sealing Material: Burrs and debris that are
created when the screws pierce the roofing panel cantear the gasketing material creating pathways for water
intrusion. It is important, therefore, that the screws bedesigned with sharp and efficient piercing points thateither prevent or minimize the creation of burrs.

•Corrosion and Head Appearance: Exposed screws
must be durable so that they do not corrode while inservice. Screws that begin to rust will, in the best case,be unsightly against the uncorroded roof panels but,in the worst case, begin to weep and leave streaks orstains of rust from each fastener. Additionally, caremust be taken in proper fastener material selection
to prevent negative galvanic interactions with someof the roof panel material types. Galvanic corrosion
can result not only in corrosion to the fastener, but
depending on the metal pairing, to the roof panel.
Once again, this could result in unsightly corrosion but
also damage to the roof panel around the screw, opening
leak pathways (See Figures 5 and 6). Head appearance
is also important and usually screws are painted tomatch the color of the roofing panels. Not all paint is
the same, however, with liquid applied paint being
far less durable than powder coated paint. Paint
type is important because paint methods that provide
poorer adhesion may be vulnerable to damage during
installation which can lead to premature corrosion.

◢ Screws•For Wood Applications: Screws for wood applications may be madeof either hardened carbon steel or stainless steel. Naturally, the stainlesssteel variety has superior corrosion resistance to those made of carbon
steel. However, the austenitic grades of stainless steel make poor choices
for self-drilling or self-piercing points. Therefore, many of these roof
screws may be made of the stronger but poorer corrosion resistant
410 martensitic stainless steel. Screws for wood to metal applications
usually have either a sharp Type #17 point or a small #1 drill point. In
either case, the point provides sufficient piercing capability to make itthrough the thin roofing panel but not enough strength to pilot holes inthicker metal trusses and purlins. These screws are usually Hi-Lo or
spaced high-thread styles of threads for easy tapping into wood. Headstyles are shared between wood and metal applications with the mostcommon head form being hex flange or washer head varieties.

•For Metal Applications: Screws for metal applications are usuallyeither hardened carbon steel or bi-metallic. Since stainless steel does
not perform well in drilling through thicker metal, screws entirely
made of stainless steel are seldom used in these applications. Insteaddrill point screws made of carbon steel are most common. There is adrill screw variant, however, that is bi-metallic with the upper body andhead made of stainless steel and the drill point and thread forming zone
made of hardened carbon steel. These are produced by friction welding
the two materials together. The lower half is hardened carbon steel andhouses the drill point and thread forming threads while the upper half is
stainless steel and houses the upper threads and head. Screws for metal
applications usually come with either a #3 or a #5 drill point. The #3point is capable of self-drilling thicknesses up to 0.210” and a #5 capableof 0.500” thick material. Like screws for wood applications the heads
are usually either a hex flange or hex washer head design.

◢ Sealing Washers•Non-Bonded: A Non-bonded sealing washer is simply a washer of EPDMor Neoprene. It can be slipped onto the screw and retained by making
the ID of the washer a little smaller than the OD of the screw. Thesewashers perform similarly to an O-ring except that the cross-sectional
geometry of these washers is not narrow and round like an O-ring but flatand rectangular like a flat washer. These washers rely on the underhead
bearing surface of the screw to distribute load and compress them. With
the head of the screw providing the only protection from exposure, they
are more prone to potential embrittlement from UV rays.

•Bonded Washers: A bonded washer adheres the EPDM or Neoprene
washer to the underside of a flat or slightly beveled metal washer. The
metal washer is slightly larger in OD and ID, so that the smaller rubberwasher ID retains it to the screw and the slightly larger OD of the metal
washer protects the rubber washer underneath from most UV exposure
as well as providing more evenly distributed compression. Naturally,
bonded washers are more expensive than the non-bonded variety.
However, neither is completely effective in protecting the rubber washer
from exposure to the elements and, most importantly, from UV radiation.

•Capped Heads: Although technically not a washer, there are somepremium roofing screws that have added a zinc-aluminum alloy orstainless-steel cap to the head. These oversize caps serve not only toimprove the corrosion resistance of the hardened carbon steel screw
below, but they fit over the rubber washer completely encapsulating itfrom the surrounding environment. In this way it is pretty well protectedfrom the elements and far less prone to embrittlement.

Figure 5: Example of Corrosion to the Roof Panels
Around the Fastener

Figure 6: Example of Corrosion to the Head of theFastener and the Metal Roofing Panel惠達雜誌

Hardware & Fastener Components - no.62/2024•103

Industry Focus >>◢ Solar Fasteners
Increasingly solar panel installations are being made on residential and commercial buildings these days. Although the screws associatedwith mounting these solar voltaic panels are completely independent of the screws used to fix the roofing panels, it is worth a mention here.
Like roofing panels, roof mounted solar panels must be firmly fixed to prevent them from being damaged or torn off in a storm or by gustingwinds. Therefore, the panels are fixed to a framework of mounting rails. These rails must be rigidly fixed to the structural underbody of theroof. The screw systems that typically make up this mounting hardware are a sophisticated combination of screw, sealing washer, bracket,and mounting nut (See Figure 7). Like the roofing screws described above, the screws in these systems are also designed with self-tapping
threads and self-piercing or self-drilling points to effectively work in wood or steel. Although usually much larger in diameter than the screws
for fixing roofing panels, these screws often are bi-metallic to provide hardened carbon steel on the portion of the fastener going into the roof
substructure and stainless steel for the portion extending above the surface of the roof. Like the exposed fastener screws, these fasteners havea sealing washer to seal the roof penetration from water intrusion.

◢ Wrap-up
Exposed metal roofing screws, although simple in concept, must address
multiple challenges. Like many similar fastening situations, there are
multiple choices for a user to make, and various levels of performance thatcan be achieved. The user, therefore, must educate themselves on whether
it is wiser in the long run to purchase a more premium fastener for theinitial installation and avoid potentially costly rework later in the life of theroof or use less costly fasteners to ease the cost of roof installation. In any
event though, there are many choices and those producing, purchasing,and installing these fasteners should know a little bit about them to be able
to make the most informed choices on how to proceed.

Hardware & Fastener Components - no.62/2024

Copyright owned by Fastener World / Article by Laurence Claus

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惠達雜誌

Figure 7: Example of Roof Mounting Solar Fastener System