What is Ballast for a Roof?
When discussing commercial flat roofing systems, the term ballast often comes up. In roofing, ballast refers to a layer of heavy material, typically gravel, river rock, or concrete pavers, that is used to weigh down the roof membrane. Rather than being adhered with glue or fasteners, the roofing system is held in place by the sheer weight of the ballast. They play a critical role in the performance, longevity, and even the appearance of certain types of roofs. You will typically find this method used with EPDM (rubber) roofing systems, though it can also apply to TPO and PVC membranes in some cases.
At R Stevens Commercial Roofing, we believe in helping our clients make informed decisions about their roofing systems. We can help you determine if this system works for your property by walking you through how this system is used and the pros and cons.
The Purpose of a Ballasted Roof System
Ballast serves several important functions in a commercial roofing system:
- Securs the Membrane
The primary purpose of ballast is to hold the roofing membrane in place. On flat or low-slope roofs, wind uplift can pose a serious risk. Ballast helps resist this force by distributing weight evenly across the surface. This helps hold the waterproof membrane and insulation down protecting from water damage.
- Protects the Membrane
Ballast provides a protective layer that shields the roofing membrane from UV rays, foot traffic, hail, and other physical damage. This can significantly extend the lifespan of the roof.
- Adds Fire Resistance
Stone ballast is non-combustible and can improve the fire resistance of the roof. Many ballasted systems meet Class A fire ratings.
- Improves Drainage and Insulation
The ballast layer can promote better drainage and reduce the heat island effect by reflecting sunlight. In some cases, it can also help insulate the roof.
Common Materials Used for Roof Ballast
Various materials can be used for ballast, each with its own specific application and look. The selection depends on the roof’s structural capacity, budget, and intended use.
- River Rock or Gravel: Rounded river stones (typically 1.5” to 2.5” in diameter) are the most common form of ballast. They are heavy, durable, and relatively easy to install. They are also cost effective.
- Crushed Stone: More angular than river rock, crushed stone is often used for its interlocking properties and better wind resistance.
- Concrete Pavers: In plazas, walkways, or green roof applications, concrete pavers serve both as ballast and as usable surface material. They’re also ideal for roofs that experience heavy foot traffic.
- Green Roofs: Soil, drainage layers, and vegetation act as the ballast creating an aesthetically pleasing and environmentally friendly roofing system that also helps with installation.
- Ballast Mats: These are rubber mats weighed with internal material. They’re less common but are used in specific commercial applications where loose rock isn’t ideal.
How is a Ballasted Roof Installed?
Installing a ballasted roof is a layered process that relies on precision and a solid structural foundation. The components are placed on the roof deck without being mechanically attached to it.
- First, rigid insulation boards are laid directly onto the roof deck. These boards are not fastened down but are held in place by the subsequent layers and, ultimately, the weight of the ballast.
- Next, a waterproof membrane, such as EPDM (a synthetic rubber) or TPO (a thermoplastic), is rolled out over the insulation. The seams of the membrane are welded or taped together to create a continuous, watertight surface.
- Finally, the chosen ballast material is spread over the entire surface of the membrane. Engineers calculate the exact amount of weight needed per square foot to counteract the highest expected wind speeds for the building’s location. A structural assessment of the building is always the first step.
At R Stevens Commercial Roofing, our contractors are experts in various roofing systems, enabling us to offer tailored solutions for different types of properties. We understand that each project is unique, and we take the time to assess your specific requirements. Whether it’s a leaking roof that needs repair or a new roof for your commercial building, we work diligently to provide efficient, durable, and cost-effective roofing options. Contact us at (973) 535 6500 to learn more about our services.
Advantages and Disadvantages of Ballasted Roofing
Like any construction method, ballasted roofing has a distinct set of pros and cons. Understanding these helps property owners make an informed decision based on their specific needs and building characteristics.
These factors often center on cost, durability, weight, and maintenance. A careful evaluation is necessary to determine if the benefits outweigh the potential challenges for a particular project.
Benefits of Using a Ballasted Roof
There are many benefits to having a ballasted roof on your commercial building:
- Cost Effective: One of the biggest advantages of a ballasted system is its cost-effectiveness. Since there is less adhesive and fewer fasteners required, you can reduce labor and material expenses upfront.
- Quick Installation: The installation is often faster and requires less labor than fully adhered or mechanically fastened systems.
- Natural UV Protection: The ballast acts as a physical barrier between the sun and the roofing membrane protecting it from degradation caused by UV exposure. This contributes to the roof’s longevity.
- Improved Fire Resistance: Stone and paver ballast systems help buildings meet stringent fire codes due to their noncombustible nature.
- Energy-Efficient: The mass of the stones or pavers helps to absorb heat during the day and release it slowly at night, moderating the building’s temperature and potentially lowering energy bills.
- Simpler Repairs: Repairs are typically simpler and less expensive. If a section of the membrane is damaged, a roofer can just move the ballast aside, fix the membrane, and then spread the ballast back into place.
Potential Drawbacks and Considerations
The potential drawbacks and considerations to a ballast roof system are as follows:
- Heavy Load: Ballasted roofs are significantly heavier than other types. A typical stone ballast roof can add 10–25 pounds per square foot to the structure. The building must be designed to support this additional load.
- Challenging Repairs: If a leak occurs, crews must move the stone to access the membrane below, which makes repairs more time-consuming and labor-intensive.
- Wind Scour at Edges: If improperly installed or maintained, the wind can displace the stone at roof edges or corners, leading to exposed membranes and potential damage.
- Vegetation Growth: Over time, dirt and organic matter can accumulate between stones, promoting weed growth or algae buildup, especially if the roof isn’t maintained regularly.
- Limited Roofing Type: Ballasted systems are also limited to flat or very low-slope roofs. On a roof with a significant pitch, the ballast material would simply slide off, making the system ineffective and dangerous.
Is a Ballasted Roof Right for Your Building?
Is a ballasted roof right for your building? The answer lies in several key facts including the structural capacity of your building, the climate where you live, and your long-term maintenance plans.
A ballasted roofing system is ideal for:
- Large, flat commercial buildings.
- Warehouses, big-box retail, and distribution centers.
- Owners seeking a lower upfront cost.
- Buildings in regions with low seismic activity and sufficient load capacity.
They are not recommended for:
- Roofs with steep slopes (over 2:12) or residential houses.
- Buildings with limited structural load-bearing capacity.
- Facilities requiring frequent roof access or equipment servicing.
- Areas with extreme wind uplift concerns (unless additional measures are taken).
Ultimately, consulting with R Stevens Commercial Roofing is the best way to determine if this roofing system is a viable and safe option for your property. We can provide a detailed analysis and recommendation. Schedule a free inspection today.
What is Ballast for a Roof?
Ballast might not be the flashiest part of a commercial roof, but it plays a crucial role in the performance and longevity of many flat roofing systems. When properly selected and installed, a ballasted roof can offer a durable, cost-effective solution with excellent wind and UV protection.
At R Stevens Commercial Roofing, we’ve installed and maintained thousands of commercial roofing systems, including ballasted EPDM, PVC, and TPO. Whether you’re building a new facility or replacing an old roof, our team can help you determine if a ballasted system is the right fit. Come see us at 1312 Pleasant Valley Way West Orange, NJ 07052.
