Besides the color and type of wall panels, you need to determine how those panels should be joined together. There are two different methods of fastening wall panels together. One costs more than the other and differences in style may recommend one over another for your specific project.
Wall panels may be joined with exposed fasteners or concealed fasteners. We’ll take a look at when to use each style of fastening, its advantages and disadvantages and the various types of fasteners available.
Exposed Fastener Panels
As the name suggests, exposed fasteners are visible and exposed to the environment. Exposed fasteners originated with corrugated sheet-metal buildings where the panels are fastened much like through-fastened roofing, using self-drilling screws or other fasteners. The wall panels are attached directly to the frame supports. Panels are two to four feet wide and limited to 40 feet in length for ease of shipping and handling.
The fastener penetrates the overlapping sections of the wall panel, locking them into place. The method is often referred to as "through-fastened." Sealant and a washer are placed between the fastener head and the surface to prevent water seepage. After installation, the fastener head remains visible against the exterior of the wall.
- Exposed fastener installation is less expensive than concealed fastener and is often found in agricultural or industrial structures where aesthetics is not a concern.
- Exposed fasteners are also quicker and easier to install than concealed fasteners, optimal for simple structures erected by unskilled labor.
- Typically used for vertical panel installation, exposed fasteners can also be used with horizontal panels as long as the selected panel has deep ribs rather than flat ribs.
While the advantages of exposed fasteners include ease of installation and low cost, there are several disadvantages.
- Since the fasteners pierce the panels, they create points where water can leak into the wall.
- Overtightened fasteners can dimple or bend a panel.
- Panels fastened with exposed screws are unable to move with temperature changes; eventually, the panel may slot around the fasteners that may cause the fastener to loosen or leak.
- Metal fatigue sets in and causes cracks and panel failure under wind loads.
Exposed fastener walls require more frequent inspection and maintenance to prevent panel failure.
Concealed Fastener Panels
Once installed, concealed fasteners are not visible on the exterior of the wall. They are hidden inside interlocking panel joints for protection from the elements, creating a smooth appearance that is more aesthetically pleasing than exposed fastener designs. The most common configuration for concealed fastener panels is snap lock joint .
Concealed fastener panels are commonly used for architectural and residential applications.
Concealed fasteners attach to the panels with clips, leaving the panel surface intact. The seams are snapped together manually. Wall panels installed with concealed fasteners are more secure than their exposed fastener counterparts because it is more difficult to reach and remove the fasteners and they are unlikely to back out during panel movement.
- Snap-together panels are simple to install and replace when needed.
- The clips used in concealed fasteners allow the panels to “float” during thermal movement, eliminating problems with metal fatigue and torn fastener holes.
- Concealed fasteners can be installed on substrates of lumber, plywood, cold-formed Cee and Zee sections, hot rolled beams or concrete and masonry.
- Concealed fastener construction typically costs more than exposed fastener construction due to the required skill and longer installation time.
The fastener’s size requirement is determined by panel and clip fastener clearances. The manufacturer’s installation guide includes the required fastener length, point and thread type according to the underlying type and thickness of the substrate.
The panels tend to be narrower than those used in exposed fasteners applications, requiring additional skill, time and materials to use. Concealed fasteners can be difficult to trim around framed openings, also taking additional time to complete.
Types of Fasteners
If the wrong fastener, whether exposed or concealed, is used the wall may suffer premature failure. Always use the fasteners specified by the steel building manufacturer; do not use substitutions that appear similar. If there is no specification, the rule of thumb is to select a screw designed for attaching into the thickness of the girt as well as long enough to allow three full threads to extend beyond the girt.
There are four critical determinants in selecting the appropriate fastener.
- Thickness (gauge) of the steel girt into which the fastener is installed, limiting the choice of fastener diameter and point configuration.
- The spacing of the girts and the fasteners along the girts determines the surface area of the panel dependent on the fastener's ability to resist pulling out of the substrate or pull the panel over the head of the fastener.
- Design wind loading determines the actual forces exerted upon the wall panel and defines the minimum strength requirement for resistance to pullout and pull-over.
- The gauge and configuration of the metal wall panel determine the diameter of the fastener head or the sealing washer to resist pull-over forces.
Fasteners may be galvanized to resist corrosion, although not all fasteners are so coated as it adds to the cost. Material performance is impacted by dissimilarities between the metal of the panel and that of the fastener, which could result in galvanic reactions.
Carbon steel is the most commonly used fastener material since it is cost-effective and has reasonable performance ability. Carbon steel allows exposed fasteners to be created with self-drilling or self-tapping points. For some applications, ductile tapping screws are produced from a special steel alloy that allows it to bend without fracturing in environments with excessive thermal movement or vibration.
Fasteners have either a pancake or hexagonally shaped head. Hex-head screws are less prone to stripping and can be used in exposed or concealed applications where clearance is not a consideration. Pancake screws are commonly used in concealed fastener situations where the joint has limited space.
Which is best, exposed fastener or concealed fastener?
It depends on the application, the skill of the installer and your budget. Exposed fasteners create an unfinished appearance that may be better for simple, work-a-day structures where looks don’t count. They are also less expensive and easier to install.
However, if weather-tightness, minimal maintenance and smooth appearance are important, concealed fasteners are the better choice.