Q&A with Peter Philippi: rooflite® and stormwater management

Posted in Blog, green roof, Interview, Stormwater on January 31, 2017

Peter Philippi, MLA, Vice President and Technical Director at rooflite®, shares information on how rooflite soil is a perfect solution for stormwater management and what makes rooflite uniquely suited to manage stormwater.

What role does rooflite have in managing stormwater on green roofs?

rooflite is engineered for excellent green roof performance, which covers a few different areas that all act together to provide significant stormwater retention volume. First, the soil is lightweight to minimize the structural impact on the building below. Second, soil properties are optimized for water retention and long-lasting vigorous plant growth which are both critical pieces to maximize stormwater retention and evapo-transpiration. These components are part of all our rooflite soil systems, and each of our systems is engineered to meet different requirements, depending on the specific needs of the green roof project.

What makes rooflite soil so well-suited for stormwater retention?

rooflite products are designed for different types of green roofs as specific soil systems that optimize water retention and plant performance at the same time. rooflite soil systems mimic natural soil profiles creating healthy root environments and vigorous plant growth. At the same time, they fulfill all the technical requirements for state-of-the-art green roof technology. We’ve spent a lot of time perfecting the balance of all the different soil requirements for a green roof, and we’ve seen great success with managing stormwater across our projects.

What makes the green roof environment unique for managing stormwater?

Stormwater management on a green roof simply means reducing the amount of water that runs off the roof into sewer systems. And our soil does a few different things – retains water in the soil for the plants, returns water to the atmosphere through evapo-transpiration, dramatically reduces peak flows, and significantly delays any remaining run-off.

What is the biggest challenge in designing engineered green roof media for stormwater retention?

Finding the right balance of properties to work for multiple and sometimes contradicting goals and requirements. For example, our soil maximizes water retention for stormwater goals, and we have to do that in a way that doesn’t jeopardize a healthy root environment for vigorous plant growth. Our soil also delays water run off to increase evapo-transpiration but also provides secure and proper drainage of surplus volumes to avoid unforeseen roof loads. One of our main goals with our soil is to be as natural as possible and technically sophisticated as necessary at the same time.

How do the plants on a green roof play into a stormwater management goal?

This is one of the most important parts of stormwater management on a green roof, and it’s often one that gets overlooked. Thriving plants and their roots contribute greatly to the amount of stormwater a roof can retain. Without healthy plants, a green roof can’t realize its full potential, and so healthy,
vigorous plant growth is essential to minimize and delay any water runoff from the roof.

What’s the soil made of to accomplish all of this?

Our rooflite soil systems are made up of a finely tuned set of materials, which vary by U.S. region but include various types of lightweight aggregates and high-quality organic components.

What is your production process to create rooflite soil?

We use a sophisticated process to produce rooflite, which has been developed through our many years of experience. Our rooflite soil systems are created  per industry standards with proprietary and consistent mixes to ensure long-term quality and success. They are also sourced, produced and shipped by our regional blender network based on locally available materials. And we design them to last. Our first green roof projects were installed in 2005 and they are still thriving.

What’s a real-life example of how your soil can effectively manage stormwater? 

An outstanding example is our deep intensive soil system. This system is typically used in large planters and containers, which can contain anything from perennials and shrubs to trees. In this system, the bottom layer consists of granular lightweight drainage, which can be designed as a water reservoir. Tree roots can easily tap into that reservoir without the need for complicated technical features like tanks, pumps and electronic controls. It’s a very efficient system that retains water for the plants and allows them to use it as necessary.

Are there specific projects where you’ve seen good success with stormwater management?

Yes. In some ways, all our projects are stormwater management success stories because each green roof we’ve installed prevents water from reaching the ground. Some of the more impressive projects that use our rooflite soil systems have made important impacts on stormwater management. A few of them are the Target Center in Minneapolis, which captures almost 1 million gallons of annual
stormwater, Nashville Music City Center, with 2.6 million gallons of annual stormwater capture, and Brooklyn Grange Farm (Navy Yard), with an annual capture of almost 1 million gallons of stormwater. These projects have made a major impact in their cities and neighborhoods in helping to manage stormwater.

Is all green roof media the same when it comes to stormwater management?

No. Our company was founded in 2005, and we’ve dedicated significant effort to perfecting our soil to meet all the different requirements – soil that’s lightweight, soil that supports vigorous plant growth, and soil that has good stormwater retention volume. We are confident that our rooflite soil systems are the best available for a variety of reasons, but one of the primary ones is that we specifically engineer them to optimize stormwater management and support healthy plant growth.