6 Best Load Bearing Pads For Under-Shim Support Pros Use

Securing heavy rooftop equipment requires more than just placement; it demands a foundation that protects the roofing membrane while distributing weight effectively. When HVAC units, piping, or heavy conduits sit directly on a roof, vibration and point-loading can compromise the structural integrity of the assembly. Choosing the right load-bearing pad prevents long-term damage like membrane punctures, deck depressions, and moisture infiltration. Proper support systems turn a potential liability into a stable, code-compliant installation that protects the roof’s lifespan.

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DiversiTech E-Lite Pad: Best for HVAC Units

The DiversiTech E-Lite pad is the industry standard for lightweight, durable HVAC equipment support. Constructed from high-density polyethylene, it offers a distinct advantage by resisting the corrosive effects of weather, UV rays, and the condensation that drips from unit cabinets.

Its design includes a textured surface that prevents equipment from sliding, which is vital when units are positioned on slightly pitched roofs. Unlike concrete pads, which are heavy to hoist and prone to cracking under thermal cycling, this pad remains flexible and maintains its shape over years of seasonal temperature shifts.

The bottom line: Use this when the project calls for a cost-effective, non-penetrating solution that won’t degrade under the constant vibration of a condenser fan.

Rectorseal Pro-Pad: Most Versatile Option

Rectorseal Pro-Pads excel in applications where uniform weight distribution is the priority. These pads are engineered with a specific density that prevents “sinking” into high-performance roofing materials, such as TPO or EPDM membranes, which can soften in the summer heat.

The versatility of the Pro-Pad lies in its ability to support various mounting configurations, from simple equipment stands to custom-fabricated metal frames. It absorbs vibration effectively, keeping noise transfer to the interior of the building to a minimum.

When the job involves delicate roofing membranes, the Pro-Pad is a reliable choice. Its surface profile is designed to minimize pressure points, ensuring the roof’s structural integrity remains intact beneath the equipment’s footprint.

Miro Heavy-Duty Pads: For Extreme Loads

Miro is the go-to for heavy-duty commercial mechanical support, especially when dealing with massive chillers or large-scale exhaust fans. These pads are built to withstand significantly higher PSI (pounds per square inch) ratings than standard plastic or rubber options.

These units often feature adjustable supports that allow for leveling equipment on uneven roof surfaces. This is critical in commercial settings where flat roofs often have subtle pitches for drainage; failing to level a heavy unit can cause internal mechanical stress and premature failure.

Avoid using lighter-duty pads for heavy, industrial equipment. Miro’s robust construction ensures the weight is spread across a wider surface area, preventing the roof deck from bowing or sagging under concentrated loads.

Cantsink KnuckleHead: Best Adjustable Support

The Cantsink KnuckleHead system stands out because of its unique, fully adjustable base. It allows contractors to level piping, conduit, or small equipment runs precisely without needing custom shims or risky, makeshift support structures.

Adjustability is a massive time-saver when working on corrugated metal roofs or older flat roofs that have developed “birdbaths” or depressions over time. The “knuckle” design allows the support head to pivot, ensuring the load stays perpendicular to the base regardless of the roof’s slope.

Choose this system when the project involves complex, multi-level piping or conduit runs that require strict alignment for proper drainage or aesthetic compliance. It is an investment that pays for itself in reduced labor hours during setup.

OMG PipeGuard: Ideal for Rooftop Pipe Runs

OMG PipeGuard systems provide a dedicated, non-penetrating solution for rooftop gas lines, electrical conduits, and condensate drains. The modular design allows for multiple pipe runs to be supported by a single block, keeping the roof deck clean and organized.

These guards are specifically engineered to accommodate expansion and contraction. As metal piping heats up and expands in direct sunlight, the pipe is allowed to slide within the support bracket, preventing the entire pipe run from buckling or tearing the roofing membrane at anchor points.

For projects where high-traffic or high-volume piping is present, the PipeGuard is the most professional solution. It keeps the roof clear for maintenance crews and prevents the common “spaghetti” of unorganized piping that leads to tripping hazards and membrane damage.

Quick-Sling Roof Block: Pro-Grade Stability

Quick-Sling blocks are widely recognized for their structural integrity and ease of installation in HVAC mounting. These blocks come pre-assembled, which reduces time on the roof and ensures that the hardware used is compatible with the base itself.

The stability provided by Quick-Sling is superior because of the wide base footprint. It effectively distributes the weight of air handlers or mini-split condensers, even in regions prone to high wind uplift.

When you need a “set it and forget it” solution, look to Quick-Sling. They offer a refined balance between ease of installation and long-term durability, making them a preferred choice for contractors who need to get off the roof quickly without sacrificing quality.

Choosing Pad Material: Rubber vs. Plastic

The debate between recycled rubber and high-density plastic often comes down to the specific roof membrane in play. Recycled rubber pads are excellent for vibration dampening and friction, but they can sometimes contain plasticizers that react negatively with certain single-ply membranes.

Plastic pads (like polypropylene or polyethylene) are chemically inert and typically safer for use on TPO, PVC, and EPDM. They are lighter and easier to transport, though they may lack the high-friction “grip” that rubber provides during heavy wind events.

Always check the manufacturer’s data sheet for material compatibility. If a chemical reaction between the pad and the membrane is a risk, ensure a separator sheet is installed underneath to provide a neutral buffer zone.

How to Calculate Load Capacity for a Project

Calculating load capacity starts by determining the total weight of the equipment, including the support frame and any internal components that hold fluids or refrigerants. This total must be divided by the number of support pads to find the PSI exerted on the roof deck.

Consult the building’s structural drawings to understand the load-bearing capacity of the roof assembly. A roof designed for light foot traffic may not handle the concentrated load of a multi-ton chiller without additional structural blocking or a steel dunnage system.

When in doubt, err on the side of oversizing the pads to increase the surface area. Spreading the load is always safer than trying to keep the footprint as small as possible.

Common Installation Mistakes to Steer Clear Of

One of the most frequent errors is failing to clean the roof surface before placing a pad. Dirt, gravel, and debris trapped beneath the pad will act like sandpaper, grinding away at the roofing membrane due to thermal expansion and contraction.

Another major oversight is not checking for proper drainage. A pad should never be placed in a way that blocks the natural flow of water to the roof drains or scuppers. If a pad obstructs drainage, water will pool, leading to premature aging of the membrane and potential leaks.

Finally, avoid fastening pads directly through the roof membrane whenever possible. Every penetration is a potential leak source; using non-penetrating, weighted systems is always the preferred standard for professional installations.

Do You Need an Engineer for Your Roof Load?

If you are adding equipment that exceeds the standard dead load for which the roof was originally designed, professional engineering is mandatory. An engineer evaluates not just the roof deck, but the underlying joists and trusses to ensure they won’t deflect or collapse under the new weight.

Many municipal building departments require a structural permit for any rooftop equipment installation. A professional review provides the necessary calculations for wind-load and point-load distribution that local inspectors look for during the final walk-through.

Do not skip this step if the installation is on a commercial building or a residential home with large, heavy HVAC components. A small fee for an engineer’s sign-off is significantly cheaper than the liability and repair costs associated with a structural failure.

Properly supporting rooftop equipment is the hallmark of a professional job that prioritizes building longevity over a quick finish. By selecting the right pad for the specific load and roof type, you effectively insulate the structure from the stresses of heavy machinery. Taking the time to calculate loads and ensure proper placement remains the most reliable way to avoid long-term maintenance headaches.