top of page
Search

How Backer Rods Can Reduce Oil Canning in Metal Roofing and Siding

Metal roofing and siding offer incredible durability, sleek aesthetics, and long-term value. However, one aesthetic issue that can sometimes plague these installations is "oil canning." This wavy, buckling appearance isn't a structural flaw, but it can certainly detract from the clean lines you expect from metal.


While it's important to understand that oil canning is largely inherent to light-gauge flat metal and cannot be entirely eliminated, there are effective strategies to significantly mitigate its appearance. And one unsung hero in this battle?


Backer rods.


What Exactly is Oil Canning?


Before we dive into the solution, let's briefly define the problem. Oil canning is a phenomenon that occurs in light-gauge flat metal, causing it to appear wavy or rippled. It's often due to:

  • Tolerances in manufacturing: Even perfectly flat sheets have microscopic variations.

  • Thermal expansion and contraction: Metal naturally expands and contracts with temperature changes.

  • Uneven fastening: How the panels are secured can influence their flatness.

  • Substrate irregularities: Imperfections in the underlying structure can transfer to the metal.

While not a structural issue, severe oil canning can be visually unappealing and lead to homeowner dissatisfaction.

Backer rods are essentially compressible foam rods, typically made from polyethylene or polyurethane, available in various diameters. They are commonly used in sealing applications to create a bond breaker and control sealant depth. But their utility extends beyond just sealants, especially when it comes to metal panels.

So, how do they help with oil canning?

  1. Providing a Consistent "Soft" Bed: When installed correctly behind the metal panel, particularly in areas where the panel might "float" between fasteners or across framing, backer rods provide a continuous, slightly yielding support. This subtle pressure helps to encourage the metal to lie flatter and reduce the tendency for it to buckle inwards or outwards.

  2. Minimizing Substrate Irregularities: If your purlins, girts, or sheathing aren't perfectly uniform, the metal panel can telegraph these imperfections. A backer rod can help bridge minor gaps and inconsistencies, creating a more even surface for the metal to rest against.

  3. Controlling Fastener Pressure (Indirectly): While you should always follow manufacturer guidelines for fastener torque, backer rods can indirectly help distribute pressure more evenly across the panel's width. This prevents localized stress points that can exacerbate oil canning.

  4. Allowing for Movement: Critically, backer rods are compressible. This allows the metal panels to expand and contract naturally with temperature changes without fighting against a rigid, unyielding surface. This inherent flexibility is key to preventing stress buildups that can lead to buckling.


Where and How to Use Backer Rods


Backer rods are most effective when placed strategically:

  • Along the underside of the panel, parallel to the ribs: This is particularly useful in standing seam systems or ribbed panels where the flat pan area is prone to oil canning.

  • At intermediate supports: Between primary framing members, a continuous run of backer rod can provide consistent support.

  • Behind flat areas of siding panels: For metal siding like Board & Batten, backer rods can be run horizontally behind the panel to provide continuous backing.


Installation Tips:

  • Choose the correct diameter: The backer rod should be slightly larger than the gap it's filling to provide gentle compression without distorting the panel. 5/8" is a great standard size.

  • Securely attach: While some backer rods are self-adhesive, others might need to be secured with a small amount of adhesive or staples to ensure they stay in place during panel installation.

  • Consistency is key: For best results, ensure the backer rod is installed uniformly along its intended path.



Important Considerations


  • Not a Cure-All: Remember, backer rods are a mitigation strategy, not a complete cure. Proper panel gauge selection, careful installation techniques (e.g., avoiding over-tightening fasteners), and a flat substrate remain paramount.

  • Consult Manufacturer Guidelines: Always refer to the metal roofing and siding manufacturer's recommendations. Some manufacturers may even specify the use of backer rods in certain applications.


By incorporating backer rods into your metal roofing and siding installations, you're adding a simple yet effective layer of defense against the visual nuisance of oil canning. It's a small investment that can make a big difference in achieving that crisp, clean aesthetic you desire from your metal cladding.

 
 
 
bottom of page