Oil Canning and Flush Metal Wall Panels

Oil canning is a broad term in the world of metal panel products and is considered one of the most vexing issues facing metal panel installations. The Metal Construction Association (MCA) defines oil canning as a “visible waviness in the flat areas of metal roof and metal wall panels.” Oil canning, also known as elastic buckling or stress wrinkling, occurs in all types of metal panels. While it is a common concern, there are steps you can take to minimize the problem.

Here, we’ll focus specifically on oil canning/distortion with metal flush wall systems, which for MBCI products includes our FW Panels and Designer Series. The type of oil canning that occurs with flush wall systems is not caused by anything dealing with the product itself or with how it’s manufactured. Rather, it is a consequence of what installers are putting the metal panels on and how the installation is done.

Installers must verify the substructure is in frame to prevent oil canning of panels.
Installers must correct any out-of-plane areas of the substructure to prevent metal panels from oil canning.

The simplest way to explain the phenomenon is that if the substructure is out of plane, i.e., not in alignment, stresses are put onto the panels that will create an appearance of oil canning. After all, as the old adage goes, you only get out what you put in. In the case of flush metal wall systems, the panels will look no better than what they are put on top of. If the substructure is wavy, out of plane, up or down, in or out, that condition will affect the panels’ performance and appearance.

Certain tolerances will have an effect on the panels’ appearance. With MBCI’s FW and Designer panels, tolerances would be 1/4 inch and 20 feet outward (away from two attachment points) and 0 inch and 20 feet inward. This means that if panels are forced into an inverted convex position, they will show stress rippling or oil canning more severely than when they’re stretched over a concave position, i.e., there can be some tolerance outward but zero inward.

With these types of panels, the biggest concerns with oil canning/distortion are aesthetics, but performance problems are also of concern, including possible engagement or sealing of the side joints.

Minimizing Oil Canning/Distortion of Panels

Prior to installation, installers should be checking the substructure with string lines or lasers and correcting or shimming any areas that are out of plane, especially since oftentimes substructures, such as stud walls or structural walls that the metal panels are attached to, are installed by other trades. Metal panel installers need to scrutinize each aspect for alignment and then either correct or shim to bring it within tolerance and within plane.

As is true with any metal panel product, for best results, proper handling and installation go a long way towards preventing the problem of oil canning in the field.

To find out more on how to minimize oil canning on your MBCI metal wall panels, contact your local MBCI representative, and sign up for our newsletter to subscribe to our blog.

Installing Metal Roofing Over Asphalt Shingles

Can Metal Roofing Be Installed Over Shingles?

When an asphalt shingle roof wears out, one of the most long-lasting solutions is to retrofit the roof with metal panels, and not remove the asphalt shingles.  While it’s a change of appearance, the metal roofing panels will provide a greater durability and longer service life.

UCI
UCI Retrofit Corporate Office installed 7.2 roof panels over the existing asphalt shingle roof

Installing Metal Roof Panels Over Asphalt Shingles

There are a number of considerations when installing metal panels over an existing asphalt shingle roof.  First, the building codes allow metal over shingles if there is only one layer of asphalt shingles.  A third roof is not allowed, so there must only be one shingle roof in place.

If you’re considering installing metal roofing over asphalt shingles, contact us today to learn more about MBCI’s panel systems.

Choosing the Correct Retrofit Metal Roofing System

Fastener choice is important for wind resistance.  As is the pull-out resistance of the deck. The panel thickness (e.g., 24 gauge), panel width, height of the standing seam, spacing between clips, and clip strength all help determine the overall wind resistance of a metal panel recover installation.  Wind design loads are specific to geographic location and height of the building; work with the metal panel manufacturer to determine the design specifications.  Importantly, use fasteners that are long enough to penetrate through the asphalt shingles and the deck by at least ½” to ensure proper strength.UCI_2

 

Because metal panels run from eave to ridge, the flatness of the existing roof can affect the appearance—the waviness—of the metal panels.  Three tab shingles are quite flat versus laminated dimensional shingles.  Consider installing a base sheet or a #30 underlayment over the shingles before installing the re-cover metal panels.  The uneven surface of the asphalt shingles can be telegraphed to the metal panels, leading to an uneven or wavy surface of the new metal panels.  And, like oil canning, it’s not a performance issue, but homeowners don’t want an unsightly roof.  Spending a few dollars on a heavy base sheet/underlayment is cheap insurance to ensure an aesthetically pleasing roof, and that means a satisfied homeowner who is willing to pay for the new roof!

Benefits of Installing Metal Roofing Over Shingles

There’s a sustainable advantage to installing metal over existing asphalt shingles.  Not removing the asphalt shingles not only saves money but also reduces the amount of waste sent to a landfill.  Roofing tear-off is one of the largest contributors to landfill waste in the U.S. And, while there’s a lot of discussion about the reuse of asphalt shingles (i.e., downcycling) in asphalt roads and bike paths, the reality is that much of the shingle tear-off is not actually reused.  For example, the Colorado Department of Public Health and Environment no longer considers asphalt shingle waste to be a recyclable material.  Not because it’s not recyclable, but because there is no significant market for its use.  These ideas will influence some homeowners, so use them when selling the idea of recovering with metal.

Installing metal panels over existing asphalt shingles is a smart choice.  Design it right, and the new metal roof could last the life of the house.

Contact us today to learn more about how our panels can be installed over asphalt shingles.

How to Help Prevent Oil Canning

Oil canning is defined as the visible waviness in the flat portion of a metal panel.  Oil canning is a visual issue, not a weatherproofing or performance issue.  However, building owners will complain about waviness in metal panels on roofs, walls, and perimeter edge metal.  Edge metal and metal wall panels are more of a concern than low-slope metal panels because edge metal and wall panels are visible from the ground.  Steep-slope metal panels and shingles are also visible, so awareness of potential oil canning is important.

Oil Canning on a Metal Roof

What Causes Oil Canning?

Oil canning can happen when unwanted stresses are introduced at fasteners, clips, and over purlins and uneven substrates.  Over-driven fasteners, clips that are slightly misaligned relative to the clip/seam interface, and too much insulation between the purlins and panels can introduce these unwanted stresses.  A misaligned panel or edge metal clip, certainly after the seam or drip edge is crimped tight, will add stresses to metal panels and edge metal

Tips to Help Prevent Oil Canning

  1. Place clips correctly: Setting clips in the proper location for edge metal and metal panels (roof and wall) is critical.  The clip needs to fit into a panel seam without forcing the vertical seam out of plane.  The clip needs to be aligned correctly and sized appropriately to not compress the vertical portion of the seam.  Clips that secure edge metal need to be positioned correctly so that crimping the drip edge won’t twist or bend the edge metal.
    Although not highly visible, low-slope structural panels can oil-can at clip locations and where insulation is draped over purlins.  Compressed insulation at purlins can “push back,” adding stress to the panel and resulting in oil canning.
  2. Consider the roof color: Sometimes oil canning is inevitable.  The color of the metal or coating won’t really make a visual difference, but darker colors panels will heat up more in direct sunlight.  This may make oil canning worse in some cases.  However, striations and small ribs (which also add strength) may help prevent or hide oil canning.
  3. Choose a thick metal: Metal thickness matters, so specify metal that’s as thick as possible to avoid oil canning.  Thicker metals are stiffer, so they may resist deformation due to unwanted stresses.  This reduces the chance of oil canning in edge metal and wall panels, which are most commonly smooth-surfaced.

For more information on oil canning and its causes, see the Metal Construction Association’s white paper on the subject, which can be found at www.metalconstruction.org.

Consider these ideas on your next job.

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