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Why are There Rocks on my Commercial Roof?

If you’ve ever looked up at a flat commercial roof and thought, “Why are there giant rocks up there?”—you’re not alone. It’s a common question among property managers and building owners, especially when you’re trying to understand your roofing system or make smart decisions about maintenance and repairs. 

At Weather Shield Roofing Systems, we’ve been helping business owners navigate roofing questions like this for over 40 years. Let’s break it down simply so you can feel confident knowing exactly what those rocks are doing on your commercial roof—and whether they’re helping or hurting your roofing system. 

What Does It Mean When There Are Rocks on a Roof?

In most cases, if you’re seeing large river rocks (we’re talking two- to three-inch stones) covering the surface of a flat commercial roof, you’re likely looking at a ballasted EPDM roofing system. 

That’s a mouthful, but it basically means the roofing membrane—often EPDM rubber—is not glued or fastened down with screws. Instead, it’s “loose-laid,” meaning it’s laid over the insulation and deck without being attached, and then held in place by the weight of the rocks. 

Think of it like a giant roofing blanket held down with river rocks to keep the wind from blowing it away. 

There are other commercial roofing systems that use gravel, such as built-up roofs (BUR), but those tend to use smaller, pea-sized stones embedded in layers of tar and felt. What we’re talking about here is a very specific type of system that uses large ballast rock to literally weigh the roof down. 

Why Would Someone Use a Ballasted EPDM Roof?

While ballasted roofs aren’t as common today, there are still very specific reasons someone might choose them especially on older buildings or in particular construction scenarios. 

The biggest reason? Avoiding penetrations into the roof deck.  

If your building has a concrete roof deck or another material that doesn’t work well with mechanical fasteners (like screws), it can be better to avoid puncturing the deck at all. A ballasted system allows you to install the roof without a single fastener going into the deck, making it an attractive option for some property owners. 

These roofs were especially popular in the past for: 

• Large warehouse or distribution centers 

• Buildings with concrete decks 

• Projects aiming to avoid adhesives or fasteners due to material compatibility or environmental concerns 

How Well Do Ballasted Roofs Hold Up Over Time?

Here’s where it gets tricky. 

Leak detection and repair on ballasted roofs is significantly more difficult and expensive than with other roofing systems. 

Why? Because if you think there’s a roof leak, you first have to manually remove the rocks to even inspect the membrane. And since water can travel between layers, the actual source of the leak may be far from where the water shows up inside your building. 

Additionally, these roofs don’t perform well in freeze-thaw climates—like we see here in Michigan. The rocks themselves tend to break down over time, creating sharper edges that can puncture the membrane when walked on. 

We’ve seen it happen: A service tech steps on a sharp rock, it pierces the membrane, and you don’t find out until water starts dripping inside. Not ideal. 

Common Problems With Ballasted Roofs

Over the years, we’ve worked on a lot of ballasted systems. And while they serve a purpose, they’re not without their quirks. 

Some of the most common issues we see include: 

• Shrinkage of the membrane: As EPDM ages, it tends to shrink. That puts stress on the perimeter walls and edge metal, sometimes pulling or bridging the membrane like a trampoline. We’ve seen membranes pull away from walls and deform metal flashing. 

• Rock migration: Over time, rocks shift due to wind, water, or foot traffic, leaving areas of the membrane exposed—and vulnerable to damage. 

• Difficult inspections: Routine maintenance becomes a major task when crews have to move rocks just to check the condition of the membrane or flashings. 

• Heavy load: Those rocks are heavy. While most commercial structures are built to handle the weight, it’s something to be aware of, especially if you’re adding rooftop units or considering a re-roof. 

Are Ballasted Roofs Still Installed Today?

Not often. They’re mostly considered an older roofing solution, and modern roofing systems—like fully adhered or mechanically fastened single-ply membranes—are more common today. 

However, there are still very specific use cases where they make sense, such as: 

• Avoiding roof deck penetrations 

• Fast-tracking a dry-in for large warehouses 

• Re-roofing over existing ballasted systems (in some cases) 

What Should I Do If I Have Rocks on my Commercial Roof? 

If you manage or own a building with a ballasted EPDM roof, it’s worth taking a closer look at its current condition. Here are some practical steps: 

• Schedule a professional roof inspection: This is key to identifying any hidden damage or problem areas—especially since leaks can be hard to trace on these systems. 
• Consider Max Life Roof Care: Our preventative maintenance program includes routine inspections and maintenance tailored for systems just like yours. It’s a cost-effective way to extend your roof’s lifespan and catch small problems before they turn into major expenses. 
• Plan for eventual replacement: These systems were built to last—but not forever. If your ballasted roof is 20+ years old, it’s wise to start budgeting for replacement. Newer systems offer better energy efficiency, easier maintenance, and longer warranties. 
• Watch the perimeter walls and edges: That’s where we see the most trouble—membrane shrinkage, lifting metal, and gaps in flashing. If you see any signs of movement or wear, it’s time to call in an expert. 

What Does Weather Shield Recommend?

At Weather Shield Roofing Systems, we’ve inspected, repaired, and replaced hundreds of ballasted EPDM roofs over the years. We’re not here to scare you—but we are here to tell you the truth: Ballasted roofs have their place, but they come with real maintenance challenges. 

If your building has one, you deserve to know exactly what condition it’s in—and what options you have going forward. 

We’re always happy to walk a roof with you, review photos, and give an honest assessment. If repairs make sense, we’ll tell you. If it’s time to plan for replacement, we’ll help you do that with a clear timeline and budget. 

No pressure, just practical advice you can trust. Contact us today!