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A well-designed green roof assembly, whether extensive or intensive, involves a series of functioning layers that must succeed in achieving the following:

The success of a green roof relies heavily on the performance of the waterproofing system. In addition to preventing water ingress, waterproofing systems must also be able to provide the building with thermal performance, roof drainage, air tightness & vapor control, and protection from any structural damage caused by root penetration. To ensure that the waterproofing membrane is protected, these systems will typically include a root barrier.

Root barriers can be used to create a protective barrier, either chemically or with a physical sheet, between the vegetation and the waterproofing membrane to protect from potential roof penetration. Physical barriers are made from dense, inorganic materials that will not break down due to bacterial activity or allow roots to penetrate. Chemical barriers contain a compound that stunts root growth on contact and therefore do not allow roots to penetrate the surface of the waterproof membrane.

Today, root barriers installed on green roofs are most commonly made of low and high-density polyethylene, often abbreviated to LDPE and HDPE. This doesn’t come as much of a surprise, especially when considering that HDPE makes up 47% of the material in all plastic milk, water, and juice bottles in the U.S. 

In addition to being a lightweight, pliable, heat weldable, and fully recyclable material, HDPE also offers outstanding tensile strength, moisture resistance, and the ability to withstand extreme temperatures. Naturally, it has proven to be a great material for green roof root barriers.

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Root Barriers for Low Profile (Extensive) Greenroof-Roofscapes®

RB20 (20 mil) is the most common root barrier product used for extensive green roof systems. It is a low-density polyethylene sheet that is ideal for systems that have typical green roof plants such as sedums, which have shallow roots and will not present a lot of penetration pressure.

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Root Barriers for High Profile (Intensive) Greenroof-Roofscapes®

RB30 (30 mil) is a high-density polyethylene sheet most common in intensive green roofs and roof gardens that will have more aggressive and larger plants like perennials and grasses. The thicker sheet provides additional protection and peace of mind that roots will not penetrate.

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Root Barriers for Specialized High Profile (Intensive) Greenroof-Roofscapes®

RB40 (40 mil) is a heavy-duty high-density polyethylene sheet that is recommended when very aggressive rooting plants are installed. This product has been used effectively with bamboo, but we recommend caution when installing bamboo on any roof due to the aggressive nature of the root system. 

*For questions regarding RB40 applications, please contact a Barrett technical representative directly.

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All Barrett root barrier products are installed in a similar manner, typically lapping the proceeding sheets a minimum of 12 inches and taping all joints with Barrett’s RB 25 Seam Tape. The barrier is to be turned past the top of the growing media to avoid roots growing around the edges of the sheet. Taping the edges is an extra measure of assurance.

These products are not biodegradable when covered and are intended to provide protection from root penetration during the life of the green roof assembly. This type of root barrier is FLL compliant. Similar to ASTM in the United States, the German FLL is an organization that has been developing and standardizing green roof technology for over 30 years.

When properly installed within one of our hot asphalt RamTough 250 and/or cold asphalt Black Pearl® Greenroof-Roofscapes®, these root barriers provide a comparatively inexpensive solution for membrane protection without compromising performance or quality.  With warranties available for up to 20 years, the solution for any green roof assembly is Barrett’s Greenroof-Roofscape®.

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NOTE: All product literature (i.e. technical & safety data sheets, specifications, application instructions, etc.) is currently available to download from the “Resource Library” on our website. 

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