The Importance of Soil Structure on Green Roofs

Posted in Blog, green roof, Soil on October 25, 2022

We take soil seriously at rooflite. We provide our clients with ASTM and FLL-certified, engineered green roof soil. Our clients know our soil will work long-term and will help their project vision come alive.

Sometimes soil isn’t given the same importance as other components of a complex green roof project with many moving parts. But without the right soil, the long-term health of a green roof project will be at risk. In the last two decades, the demand for engineered soil has significantly increased due to problems associated with using natural soils, such as compaction and poor drainage. 

So why is soil so important? Soil has a basic set of properties – hydrological, physical, and biological – that are all interconnected and determine whether a soil will last into the future. We all know you need good soil for plants to grow, whether it’s a house plant or an outdoor landscape design, but the equation changes quite a lot when you move soil to a roof.

One of the keys to creating a long-lasting green roof soil is a focus on the proper blend of soil aggregates and structure. At its most basic, soil structure is the arrangement of the solid parts of soil and the pore space between them. Over time, many “normal” soils will break down because of environmental stress, compaction, irrigation, or exposure to the elements. For projects at-grade, you may be able to replenish soil now and then as these forces negatively affect the overall soil quality. On a green roof? Or in a large permanent planter? That’s not so easy.

Soil structure is often the determining factor on how a green roof performs over time. That’s why we’ve spent so many years perfecting the structure of our rooflite soil products. Green roof soil is a precise mix of organic materials and lightweight aggregates. Too much organic material, for example, will cause the soil to break down more quickly. Too little of aggregates creates an environment without enough support for the plants because it affects air and water exchange. 

rooflite products combine the perfect mix of lightweight aggregates and organic materials. The lightweight aggregates support microorganisms and retain both water and air while the organic material is the right amount for plants to remain healthy. The combination provides an ideal environment for plants to grow and thrive over time.

The key to a long-lasting green roof is the right soil with the right structure to support your plants and overall project vision.