6 Best Galvanized Shims For Leveling Roof Supports

Leveling a roof support system is rarely a perfect science, as structural framing often shifts, bows, or settles over time. Relying on makeshift materials like wood scraps or plastic shims creates weak points that invite long-term structural failure and moisture infiltration. Using proper galvanized steel shims ensures that load paths remain intact and the assembly remains impervious to the elements. Selecting the right shim is the difference between a roof that performs for decades and one that develops sagging support columns or uneven load distribution.

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Precision Brand Slotted Steel Shims: Best Overall

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These slotted shims are the industry standard for a reason: they offer a perfect balance of consistency and versatility. The slotted design allows for rapid installation around existing anchor bolts without the need to fully remove hardware.

Precision Brand provides a wide range of thicknesses, which is critical when dealing with slight variances in base plate elevation. They are cold-rolled for high compressive strength, meaning they won’t crush under the weight of heavy steel rafters or roof-mounted equipment.

For projects where the base plate must be perfectly plumb before grout or sealant application, these shims provide the necessary stability. Stick with the standard carbon steel galvanized finish for interior-protected zones, or opt for stainless variants if the shim will sit in a high-moisture drainage path.

Dayton Superior T31 Horseshoe Shims: Pro’s Choice

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Dayton Superior focuses on the heavy-duty demands of commercial structural steel. The horseshoe shape is engineered to provide maximum surface contact area once the nut is tightened down, reducing the risk of point loading on the shim itself.

These are favored by steel erectors because they stack reliably without slipping or walking during the torque-down process. When setting large-scale roof support columns or heavy beam connections, this predictability saves significant time on the job site.

The durability of these shims holds up even when subjected to the high-pressure loads common in industrial roof assemblies. Avoid the mistake of using cheaper, thinner alternatives that might deform under high torque, as that deformation often leads to loose connections over time.

Custom Hot-Dip Galvanized Plates: Max Durability

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When a roof support sits in an area prone to standing water or constant condensation, standard plating often fails. Custom hot-dip galvanized plates offer a thicker layer of zinc protection compared to standard pre-galvanized sheets.

These are essential in coastal environments or near chemical exhausts where salt or acidity can accelerate corrosion. If the roofing system involves a flat membrane like TPO or EPDM, the integrity of these shims is paramount because they are often buried under ballast or insulation.

While they may require a slightly longer lead time for custom orders, the peace of mind is worth the cost. Always match the shim material to the base plate material to avoid galvanic corrosion, which happens when two dissimilar metals touch in the presence of an electrolyte.

U-Shims Steel-U Leveling Shims: Easiest to Install

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U-shims are designed specifically for speed when working with anchor bolt patterns that are already set in concrete. The U-shape allows the shim to slide horizontally under a plate, which is a major advantage when headspace is limited or when the assembly is too heavy to lift significantly.

These shims are often used in residential deck or roof patio framing where small adjustments are needed to ensure a level walking surface. Because they are lightweight and easy to carry in a tool belt, they minimize the back-and-forth trips to the truck.

Be mindful of the gauge thickness when choosing these for structural applications. While they excel at leveling light-gauge steel, they are not designed to bridge massive gaps in heavy-duty primary framing.

The Steel Supply Co. Slotted Shims: Budget Pick

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For contractors working on high-volume projects where costs are strictly managed, The Steel Supply Co. offers reliable performance without the premium brand markup. These shims provide consistent dimensions across every piece in the bag, which is rare at this price point.

Consistency is key when you are shimming a long run of purlins where each support must meet an identical elevation. If the shim thickness varies from one piece to the next, the entire slope of the roof or support beam can become compromised.

While they lack the heavy-duty certification of some industrial brands, they are more than adequate for light-to-medium structural loads. Just verify the load-bearing requirements of the specific roof section before committing to a lower-cost option.

Meadow Burke Full Steel Shims: For Heavy Loads

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When dealing with massive structural loads—such as large-scale HVAC roof curbs or heavy-duty solar array mounting systems—full steel shims are the only responsible choice. Unlike slotted or horseshoe shims, a full shim plate provides 360-degree support under the base plate.

This eliminates any stress concentrations that can occur when the load is concentrated solely on the bolted areas. By spreading the load across the entire footprint of the base, the risk of cracking the concrete below or buckling the support plate is virtually zero.

These are mandatory for critical connections where structural engineers have calculated precise load distributions. Expect a tougher installation process, as they often require fully lifting the assembly, but the structural integrity provided is unmatched.

How to Choose the Right Shim Thickness and Size

The golden rule of shimming is to keep the shim stack height to an absolute minimum. A stack of thin shims will always be less stable than a single, thicker plate.

• Measure first: Use a laser level to determine the exact gap across all support points before sourcing your shims.
• Match dimensions: Ensure the shim width is at least equal to the width of the base plate it is supporting.
• Consider load capacity: Use thicker, solid plates for primary structural columns and thinner, slotted shims for secondary framing or leveling of support hardware.

If you find yourself needing more than three shims per bolt, rethink the base plate or the framing strategy. Excessive shimming is usually a red flag for a poorly installed foundation or base support.

Hot-Dip Galvanized vs. Electro-Galvanized: Which Lasts Longer?

Understanding the galvanization process is vital for the long-term health of your roof structure. Electro-galvanized shims have a thin, uniform coating applied through an electrical current, while hot-dip galvanized shims are submerged in molten zinc.

Hot-dip galvanization is significantly thicker and provides a sacrificial barrier that lasts much longer in exterior environments. If the shims are exposed to the elements, always spec hot-dip.

If the shims are tucked away inside a conditioned crawl space or under a fully sealed roof curb, electro-galvanized options are usually sufficient. Don’t waste money on over-specified materials, but never cut corners where moisture is present.

Best Practices for Installing Structural Roof Shims

The secret to a successful shimming job is stability. Always ensure the bearing surface is clean of debris, ice, or loose concrete before placing the shim.

Once the shim is in place, the anchor bolt should be tightened to the manufacturer’s specified torque. Never “over-torque” to compensate for a shim that is slightly off; this can warp the base plate and negate the leveling work you just performed.

If the gap between the structure and the foundation is significant, consider using a high-strength, non-shrink grout to fill the void after the shims are set. This locks everything in place and provides a solid, uniform bearing surface that won’t vibrate loose over time.

Shimming and Code: Load Path and Bearing Essentials

Building codes are unforgiving when it comes to load paths. Every ounce of weight from the roof must be transferred cleanly through the supports and into the building’s foundation.

When a shim creates a gap in that path, it acts as a lever point, putting shear stress on the anchor bolts. Ensure all shimmed connections are inspected as part of the overall structural package, especially in seismic or high-wind zones.

If you are unsure whether your shimming approach meets local code requirements, consult the structural drawings or an engineer. A small, unapproved shim stack can become a major failure point during a storm, turning a simple leveling task into a massive liability.

Roof support is only as good as the bearing points beneath it, and choosing the right galvanized shim is a fundamental step in ensuring long-term structural integrity. By prioritizing material quality and correct installation techniques, you secure the assembly against both premature failure and the hidden dangers of environmental corrosion. Keep the shim stacks low, match your materials to the environment, and always maintain a clear, unobstructed load path to the structure below.