If you’ve ever been involved with a green roof project, you know there are a lot of moving parts that go into a successful project. Each component of a green roof, from the roof layer on up to the soil and plants, is an integral part of bringing the project to life.

In our view, the green roof soil is one of the most important parts of a green roof project, and it’s not just because we produce green roof soil.

Why? Because using the wrong green roof soil can cause a lot of problems, not just with your plants but with the overall green roof installation.

We like to think most people involved in a green roof project know how important the soil is, but sometimes, people don’t focus on it nearly as much as the other technical pieces. That’s a mistake.

Imagine every single piece of your green roof is perfect – the decking, the waterproofing membrane, the irrigation system, the lighting, the benches, the pavers – but your green roof soil isn’t optimized for a rooftop installation or isn’t made up of high-quality ingredients. Using green roof soil that isn’t high quality can ruin your project and cause you a lot of time and expense to correct it.

So what do we mean by high-quality green roof soil?

To start, it’s engineered soil that is designed to meet several goals:

• To be lightweight
• To retain and drain water
• To contain the right amount of nutrients for the plants of the roof
• To be long-lasting for long-term success of the green roof

That makes sense, right? But how can you tell if your soil provider is producing high-quality green roof soil?

There are a few ways to be sure.

First, your green roof soil provider should be designing its soil according to industry standards.

These standards include ASTM E2777-14 (Standard Guide for Vegetative [Green] Roof Systems) and the FLL Green Roofing Guideline (Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. [FLL] Landscape Development and Landscaping Research Society, 2008). You’ll want to be sure they are using these standards to create and produce their green roof soil.

At rooflite, we design and produce all our green roof soil products to meet these standards. The test methods and performance standards we use are considered state-of-the-art within the worldwide green roof industry, backed by decades of testing, research and development in the field.

Second, you want to understand what testing protocols they use.

In order to know that green roof soil will stand up to the rigors of a rooftop environment, you want to be sure your soil provider has a regular testing program for their soil.

At rooflite, we’ve developed a rigorous Quality Assurance Program (QAP) to make sure that every bit of rooflite soil we produce and deliver meets our high standards and the high expectations of our customers. With a proprietary mix for each product, we are able to guarantee that every batch of rooflite soil produced is consistent across all our blender network.

Our QAP involves both internal and independent laboratories to ensure the performance of our soil. Our internal lab analyzes our rooflite soil products on a regular schedule to ensure they will stand up to demanding green roof applications throughout the life of a building. Independent labs validate compliance with established green roof media specifications and performance requirements.

We’ve designed our QAP to deliver the best products possible to our customers and to ensure they will perform well over many years.

Third, you want to ask for a green roof soil test report.

A test report will show a soil analysis that details the particle size distribution of the soil, dry weight density, density at maximum water-holding capacity, total porosity, and air-filled porosity. It will also provide details on pH, soluble salts, organic matter, phosphorous, potassium, calcium, magnesium, nitrate, and ammonium. A soil test report will give you a good, baseline view into how the soil will perform on a green roof.

We also recommend you ask for details on the lightweight aggregates used, including whether they pass a freeze/thaw process, whether perlite, vermiculite, or styrofoam are used, which can cause issues during heavy rain events, and details on compost used, including test data and the amount of wood particles used, which can cause compost to degrade over time.

At rooflite, we are always happy to provide a green roof soil test report or coordinate with you so you can conduct your own testing. We stand by our products and know they will perform well for your project.

For almost 20 years, we’ve been creating and producing high-quality soil for green roofs. We know a lot about what goes into developing green roof soil that will work, that will have longevity, and that will help you create your green roof vision.

Knowing more details on how your green roof soil provider develops green roof soil and knowing what’s in the green roof soil will set you up to have a successful green roof project for many, many years to come.

Interested in how rooflite can help? We offer a full range of green roof soil products for a variety of green roof applications. Our products are developed to meet our high standards and the high expectations of our customers.