Overburden systems, any material or assembly installed above the roofing membrane, have become an integral feature of modern building design. From green roofs and pedestal paver plazas to outdoor amenity decks and solar arrays, overburden assemblies offer aesthetic, environmental, and functional benefits. But while these rooftop enhancements are highly visible and often the focus of the roof, what lies underneath them is more critical to long-term success.
When specifying traditional exposed roofing, much of the structure below the roof drive that roofing system—what we refer to as "bottom-up" considerations. However, when the roof includes overburden, the approach must incorporate "top-down" considerations as well. Do we have a vegetated overburden with potential for aggressively rooting plant material? Are we storing stormwater for a period or indefinitely? Do we have point loads with hardscape solutions? All of these considerations will help us to determine the best membrane technology for the application.
The roof overburden systems put significant and continuous loads on the roof and create challenging conditions for water management. Moreover, once the overburden is in place, gaining access to the waterproofing membrane becomes labor-intensive and costly for maintenance and replacement. That's why waterproofing beneath overburden must be approached with proper design, planning, and incorporating high-performance materials.
Why Waterproofing Beneath Overburden Is Uniquely Demanding
Waterproofing/roofing solutions beneath membranes have two fundamental functions: keeping the structure watertight and maintaining comfort through insulation (if the space is occupied). Designing a commercial roof with overburden is not just about selecting attractive finishes; it is a matter of robust system engineering. While all roofs require reliable waterproofing, those under overburden face intensified risks, including:
- Constant Load: Unlike conventional roofs, overburden systems apply continuous weight on the waterproofing membrane, which can lead to compression-related wear, fatigue, and eventual failure if not properly accounted for.
- Water Retention: Vegetated roofs and pedestal paver systems may retain moisture by design or incidentally, creating a consistently moist environment where water may sit for extended periods. This constant exposure increases the risk of leaks and damage.
- Limited Access: Once the overburden is installed, accessing the membrane for inspection or repair is a major undertaking. Excavating soil or removing heavy pavers can be time-consuming, expensive, and disruptive. This makes early prevention and long-term durability important.
Because of these factors, the consequences of membrane failure in an overburden system are exponentially more severe than in a conventional roof. That's why designing and selecting the right waterproofing solution from the outset is crucial.
Design Considerations for Overburden Waterproofing
Effective overburden waterproofing should start during the design phase with the input from the critical stakeholders, not as an afterthought after the overburden concept is finalized. Roofing assemblies must be engineered to anticipate the unique stresses that overburden will introduce. That includes:
Evaluating load-bearing capacity
Ensuring the membrane is puncture-resistant enough to withstand installation abuse and long-term pressure
Accounting for water retention and drainage strategies
Specifying materials resistant to root intrusion (especially for green roofs)
Design teams should also consider how the overburden will impact future maintenance. Can inspection ports be incorporated to ensure that drains and other critical elements of the roof can be inspected and maintained regularly? How can components be modular or phased to allow localized access if repairs are needed later? Is a leak detection monitoring system advisable?
These considerations must be incorporated into the project strategy early on. Reactive design choices later in the process often lead to cost overruns and performance shortfalls.
Selecting the Right Waterproofing System: No One-Size-Fits-All
With the stakes so high, the selection of a waterproofing membrane should never be a generic choice. Site-specific variables such as the deck, insulation, coverboard, climate, structural slope, anticipated foot traffic, overburden type, and intended use of the space should guide every waterproofing decision.
As a leader in high-performance waterproofing solutions, Siplast understands that no two overburden applications are the same. Overburden adds complexity to waterproofing design, making membrane selection and installation critical. Removing overburden to locate and repair leaks can be difficult and costly, so getting it right the first time is essential.
Siplast promotes membrane systems that are designed for buried applications, feature monolithic installation, and often include reinforcement and redundancy to help ensure watertight performance. Proper membrane selection, integrity testing prior to placement of the overburden(such as flood testing or electronic leak detection), and protecting the membrane during installation are key to long-term success.
To address the diverse demands of overburden conditions, Siplast offers a portfolio of waterproofing systems engineered for durability, reliability, and performance:
Teranap: The Teranap Waterproofing System is compatible with a wide range of overburden assemblies, including vegetated roofs, pedestal pavers, poured-in-place concrete, stormwater management systems, mortar-set pavers, and even road-grade asphalt. Made with durable SBS-modified bitumen and reinforced with non-woven polyester, Teranap is root-resistant and designed to perform in soil- and moisture-rich environments.
Parapro® Roof Liquid-Applied Waterproofing: The Parapro Roof and Flashing Membrane system is a seamless, fully reinforced solution consisting of a primer (if needed) and two layers of PMMA resin that encapsulate a polyester fleece. This creates a high-mil-thickness membrane with excellent flexibility and resistance to water intrusion. Parapro is ideal for vegetated roofing assemblies and offers inherent root resistance, making it well-suited for both extensive and intensive green roof applications and stormwater management systems that may retain water indefinitely
PA-750 Hot-Applied Waterproofing: The PA-750 Hot-Applied Rubberized Asphalt Waterproofing System is designed for use over approved, properly prepared substrates in plaza decks, protected membrane assemblies, and other covered conditions. It provides a fast-setting, fully bonded, monolithic membrane that delivers continuous coverage and exceptional adhesion to the substrate, which is key for withstanding the demands of vegetated roof and amenity overburden, ensuring long-term waterproofing performance.
Each of these waterproofing technologies has unique performance, installation, logistical, and cost considerations that may make it preferable for a given project over another. This project specific approach ensures durability, simplifies maintenance planning, and controls long-term costs.
Best Practices for Long-Term Performance
To ensure long-term success when designing overburden assemblies, consider the following best practices:
Work with manufacturers early: Engage partners like Siplast during the design phase to review system compatibility, transitions, and load concerns.
Design for drainage: Plan for water to move away from the membrane quickly. Incorporate drainage mats, slope-to-drain strategies, and overflow protection.
Consider protection layers: Use slip sheets, root barriers, or insulation boards to protect the membrane from overburden elements.
Plan for maintenance access: Even if direct membrane access is limited, incorporate inspection ports or leak detection where feasible.
Plan for adequate loads: Not all overburden assemblies have the same weight. Understanding the load that the overburn will impose on assemblies is critical to address in the design stages.
Waterproofing Is the Foundation for Overburden Success
The demand for rooftop amenity spaces, green roofs, and other overburden systems continues to rise. But focusing solely on aesthetics is not enough. The success of any overburden assembly depends on the careful design and engineering of the waterproofing membrane beneath it.
Every successful overburden system starts with a high-performance waterproofing solution—one that accounts for weight, moisture, accessibility, and long-term durability. With no margin for failure, choosing the right membrane is not just a technical detail. It is the foundation of the entire roofing strategy.
Waterproofing under overburden is never one-size-fits-all. It requires a solution engineered for your project's specific demands. With decades of proven performance, a portfolio of specialized systems, and expert guidance from design through installation, Siplast is a trusted partner in building roofs that perform from the bottom up and from the top down.
