There are three roof configurations available for selection when installing a metal roof. Although roof panels come in any color or texture you may desire, the method of fastening the panels together determines the cost, the appearance and the durability of the joints.
Roof panels can be standing seam, batten seam or through-fastened.
A standing seam metal roof looks just like it sounds; the seams are standing up from the flat part of the panels. Standing seams can be up to two or three inches taller than the panel and act as water channels. The seams can be rolled into double-locked joints, rather like the seal on an aluminum or steel can. Other seams snap together and contain a continuous bead of sealant within the seam.
Standing seam roofs are created from vertical panels that run from the peak of the roof to the eave, or valley-to-hip. Available rolling tools allow panels to reach more than 40 feet in length, and since the standing seam roof does not require a solid substrate, standing seam is appropriate for large roofs with long spans.
Standing seam panels may be manufactured with a specific edge profile to allow the connections to snap together. Modern manufacturing methods ensure tight tolerances within the joint, further reducing or eliminating the chance for moisture to enter the seam. Other methods of interlocking panels in a standing seam roof have also been developed.
Examples of Standing Seam Profiles
- Original double-folded
- Horizontal seam single-fold
- Bulb seam
- Trapezoidal rib
- “Tee” seam
- Applied cap seam
Once the panels are joined, they are indirectly attached to the roof using concealed clips formed into the seam. The standing seam design protects the fasteners from the weather and provides a finished look to the roof.
- Standing seam is appropriate for areas with abundant rain and moisture.
- This configuration reduces the number of seams required, reducing access to water.
- Standing seam is easily modified and has a uniform appearance.
Standing seam roof panels can be obtained in any color, texture or profile to create the appearance of everything from shake shingles to roof tiles. A standing seam roof profile also includes roof panels with vertical legs or lift pans and trapezoidal seams.
A batten seam is created by bending the edges of adjacent panels upward 90 degrees and snapping a cap over the upturned edges. So where did the term “battened” come from? In the past, the space between the mated edges was filled with a wooden batten strip. Now the space is left open for hidden panel clips.
The batten seam was developed to protect against the snow and ice that sometimes damaged the typical standing seam roof. The batten strengthened the seam and increased its durability. A batten cover or cap is placed over the seam to complete the joint.
- Batten seam is made up of a framework below the roof where the metal panels are mounted between a raised batten strip.
- Today’s batten seam is all metal.
- Batten seams are effective in removing water because these roofs are generally sloped.
- Batten seams also provide superior wind resistance.
- They can be used in architecturally complex or non-traditional roof designs.
The seam is visible but has a more finished appearance than the standing seam roof, while remaining a simple and economical roof. Batten seam roofs lend themselves well to modular construction. It is typically considered an architectural roof design.
The batten seam roof has a variation called a batten roll, which uses a raised “lap seam” that is formed into the panel.
A through-fastened seam configuration is one in which one roof panel overlaps its neighbor at the edge. The panels are joined by a bead of sealant. The seam is then fastened to the roof purlins, leaving the fastener exposed to the environment. Another name for this configuration is lapped seam.
Lapped seam or through-fastened roofs are the simplest and least expensive of the roof seam configurations. They are most often found on structures with very basic functionality. One variation of the through-fastened roof is the flat seam. In this configuration, the panel edges are bent 180 degrees and hooked together. The resulting seam lies flat along the roof.
- Through-fastened roofs are connected directly to the purlins.
- The fasteners are threaded.
- The fastener punctures the edges of the joined panels, moving through the panels.
- A washer is placed between the head and the panel to prevent water from entering the opening.
Through-fastened roofs are prone to leaks when they are not properly maintained. The very nature of a through-fastened panel includes an opening through which moisture can enter the building. Steel roof panels are protected against moisture damage as long as the surface is not interrupted, but when the fastener self-drills a hole, the interior edges of the panel are exposed to the environment.
Also, the fasteners may back out of their holes due to thermal movement of the roof panels during temperature changes. The heads of the fasteners may rust and corrode. Additionally, the washers deteriorate in the weather. At least once a year, a through-fastened roof requires inspection to tighten fasteners, find holes with missing fasteners and replace worn washers.
Besides the seams, roof panels are often strengthened with the addition of ribs of various shapes and sizes roll-formed into them. When oriented vertically, the ribs and seams can divert ice, water and snow, mitigating the effect of ice dams that can pry open a panel and allow water to enter the structure. Ribs are another way of creating visual distinction between roofs.
Steel roofs are highly durable and long-lasting roofing solutions that can last the lifetime of the structure if properly maintained. The methods used to fasten together adjoining panels create unique yet uniform appearances. Through-fastened roofs are the least costly choice but require more maintenance while standing seam roofs provide excellent protection and minimal maintenance but at a higher cost.
Regardless of the seam configuration, you can have a roof with any appearance you want that weighs less on your foundation, frame and pocketbook than traditional roofing systems.