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Standing Seam Roof Guide Part 1: Panel Design

January 18, 2019

If you are tired of re-roofing your home and want to do it for one last time, you are most likely considering a Metal Roof. After all, they do last a lifetime, and standing seam is the most common and economical form of  metal roofing used in Texas and the rest of the United States. It’s a great roof style for Texas, that is popular in San Antonio, Hill Country, Coastal Bend, and The South Texas Valley.

Not all Standing Seam Metal Roofs are the same. 

We hope that with this series of short blogs on the Standing Seam subject, you can become an informed buyer of a metal roof for your home.  Today’s edition will be about what makes a roof “Standing Seam”, and how to pick the best panel shape.

So, what is Standing Seam Metal roofing? It’s a mostly flat sheet of metal that is rolled into a pan shape with “seams” on the left and right sides of the panel. These seams allow the panels to be attached to each other. The panels are applied to the roof deck in a vertical orientation, from the eave (bottom) to the ridge (top) of the roofing deck. They may or may not be painted, and can be fastened down in number of ways.

Now that’s a very loose definition, and therein lies the problem. The more broad the definition, the more room for variation, and ultimately, quality. I like to divide standing seam into two basic categories:

  • Premium Standing Seam” usually referred to as Snap Lock, Click Lock, or Mechanically Seamed.
  • “Pseudo Standing Seam” usually refereed to as “AP” Panel, “CP” Panel, 5V Crimp, and any other branding name that a manufacturer wants to put on the product and not call it true “Standing Seam”.

Most of these variations in panel style, are a reference to the shape the panel is rolled into. Panel shape plays a large role in roof performance. In premium standing seam, the panels are mostly flat in the center, possibly with some ribs rolled into it (more on that later), and the left and right sides turn up vertically, and are then folded or snapped into each other. This connection covers the joint between the two to panels, where they are locked or folded into a closed position.

Seam Style

Snap lock, the metal is shaped to have a male and female end on them, so, when one is pushed down over the other, the lock is snapped in place. When you pull up on the panel it will not come loose. See the cross section image below.

Mechanically Seamed, the metal is shaped with an exposed tongue or tang, that when folded around the neighboring panels shape, locks the two panels together. See the image below.

AP and CP Panel, the letters in the name indicate shape of the seam. One side of the panel forms an A shape and the other side a P. The A slips over the P shape, so, that all that is visible, is the A shaped seam. This shape looks fine from the exterior, until you understand that the panels leak resistance is only as good as the height of inner P shape. That height is typically only half an inch. This is dangerously low for wind driven heavy rains in a strong storm. The wind pushes the water up inside the seams and it spills over the lower half inch barrier See the image below.

5V Crimp, Is aptly named. Bend five V shapes into a panel and that’s it. With the seam height being just half an inch, and no closing of the seam, leak resistance is at a minimum here. It’s simplicity made it a mainstay in early metal roofing, where it served a purpose. Today 5V panel is mainly an agricultural application, but surprising, homes are still roofed in this manner.

A Critical note on seam height

Seam height is a major factor in leak resistance. The higher the seam height, the farther water must go up until is leaks over the edge of a panel and possibly into the underside of the roof. Seam height can vary by region, and be as low as a half an inch and go as high at two and a half inches, for special applications.

For the Texas market, one inch (1″), and one a half inch(1.5″) is common. At AL-CO, we run an inch and a half (1.5″) seam height for better leak resistance. Other companies choose to use one inch, for the sake of saving on material costs. Just think how much a contractor would save if you cut half an inch off each side of every roof panel on an entire roof. Al-CO would rather error on the safe side when it comes to leak resistance.

Ribs and Striations

Standing seam panels can come with ribs or striations rolled into the shape of the panel. The main purpose is to eliminate the waves in the shape of a metal panel. These ribs can be a simple line or two in a panel or a series of low V shapes, that run the entire width of the panel.

Reasons to have ribs in a standing seam panel:

  • The thinner the panel the more likely it is to appear wavy on a roof. So, if a contractor saves money on using a thinner metal, they simply add ribs to make it appear more flat.
  • Wider panels tend to be more wavy, and some contractors will choose to use a wider panel to save on material costs. Ribs are added to combat the waving issue. These wide panels are actually intended for commercial use. The panel size is more efficient to install on a lager building and looks like the correct sized panel on longer roof lengths. Panels of this width tend to look to big for most homes.
  • Some ribs look fine on a standing panel, but excessive ribbing can look busy on a residential home.
  • Not all standing seam panels need ribs. Thicker will ripple less, and panels that are not too wide (12-16 inches), tend to show less waves.
  • Your house’s decking can play a big factor in how the panels will lay. The flatter the deck, the less wavy the panel will appear. A contractor your decks condition, when making a panel recommendation.

In Review

  • Seam height is a major factor in keeping water out. Seams above one inch are preferred, stay away from lower seam heights, such as half an inch.
  • Seams that are snapped ore locked mechanically fastened to each other are stronger.
  • Just because a seam “looks” tall, doesn’t mean its holds out more water. Pick the right type of seam style.
  • Ribs and striations have their place in metal panels, make sure they are there for the right reason.

If you would like AL-CO Metal Roofing to give you a quote or have any questions about this blog or Standing Seam roofing in general, click the link to contact us: https://www.alcometalroofing.com/roofing-estimate/

Please stay tuned for the next installment of the Standing Seam Roofing blog from AL-CO Metal Roofing. Next time, we will be talking about Material Choices in Metal. See you then!

Chuck Roberts is a 21 year metal roofing expert, who has worked in all phases of the industry, from installing, to fabrication, to manufacturing, and contracting.  email: chuck@alcometalroofing.com or call the office: 210-605-5671