Green Roof Drainage Board

Green roofs are amazing ecological solutions that transform buildings into thriving, breathing ecosystems. But, there’s one crucial component that is often overlooked: the drainage layer.

Cuspated, waffle-like plastic drainage layer materials come in two forms: drainage plates and drainage mats. The latter are flexible composite materials packaged into rolls and include a filter fabric on one or both sides.

1. High-Density Polyethylene (HDPE)

Known for being extremely tough and abrasion-resistant, HDPE is also lightweight and waterproof. It’s used in a wide range of applications and industries, including packaging, plastic bags, and water pipes. It’s also used to make playground equipment and furniture, due to its excellent chemical resistance properties. Because of these properties, HDPE is often considered safer than other types of plastics.

Most people are familiar with HDPE through plastic water bottles. It’s ideal for these products because it won’t leach into the drink’s contents and it’s safe to recycle. It’s also used to make rope, corrosion-resistant piping, and geomembranes. It’s resistant to mildew, rot, and insects and it holds up well against chemicals.

HDPE is made through a process of polymerisation using one of several different catalysts such as Ziegler-Natta, chromium/silica or metallocene. The resulting material has a relatively low degree of branching, which gives it stronger intermolecular forces and better mechanical properties than LDPE, as well as higher strength, density, and temperature resistance.

Green roof drainage boards, which are usually made of HDPE, contain perforations for drained surplus rainwater and high capacity dimples (height c.40mm) for water retention. The drainage plates are laid between the nonwoven geotextile and the root holder foil without overlapping on these two layers. The drainage plate is then covered with a geomembrane.

2. Nonwoven Geotextile

A green roof drainage board requires a separation fabric, and nonwoven Green roof drainage board geotextile is one of the best choices. Nonwoven fabrics are available in many different thicknesses and designs, allowing you to choose the one that meets your specific needs. They separate growth media from drainage media and help to keep the soil in place, while allowing rainwater to pass through. Most geotextiles are available with test results for permeability and water flow rates, which are important considerations when selecting a fabric for your green roof project.

Woven geotextiles are made by weaving together polypropylene tapes in a crisscross pattern, which makes them super strong and hardwearing. They’re a great choice for separation applications, such as under patios or paths, and are often used in traffic areas to prevent mud build up. They also have a high tensile strength, meaning they can hold a lot of weight.

Woven and nonwoven geotextiles perform a variety of functions, including separation, filtration and reinforcement. They can also be combined to provide multiple functions, such as a drainage, root barrier and soil filter. This is a common approach on larger projects where space and budget are limited. For example, the Southeast EcoManor in Atlanta features a green roof system that combines drainage, water retention, root barrier and soil filter fabric into a single product.

3. Root Holder Foil

The drainage layer is one of the most important components of a green roof. It ensures that the growing medium is not saturated and prevents the waterproofing membrane from being damaged by the roots.

Several drainage layer options are available for different goals regarding water retention. Our specialists will advise you on the most suitable solution for your project.

The ArchiGreen SedumDrain 25 drainage board is a multifunctional water reservoir and runoff-delay drainage layer for extensive, semi-intensive, and intensive green roofs as well as paved surfaces subject to vehicle traffic. It is made of recycled high-impact polystyrene (HIPS). The top surface of this drainage layer has precise 2 mm perforations, which serve as diffusion openings. In addition, it has raised shoulders all over the drainage cell that function as a water retention and attenuation element.

These shoulders slow down the stormwater flow and allow it to be used by plants for longer periods of time, which also helps to avoid anaerobic soil conditions.

This drainage core provides a complete green roof system in one easy lightweight product. It combines drainage, aeration, water storage, root barrier, and waterproofing membrane protection in a single layer. Moreover, its unique waffle pattern and filter fabric top layer prevents the growing medium from clogging the drain. The drainage core is bonded to the non-woven geotextile for additional protection against root pressure.

4. Filter Geotextile

A filtration geotextile is a layer that prevents soil particles from migrating into the drainage system. In loose or gap graded soils, groundwater flow can carry these fine soil particles toward the drain where they may clog the system. Geotextile filters provide alternatives to graded filter media.

US Fabrics offers a wide variety of needle punched nonwoven and woven geotextiles that can serve as effective filter fabric for green roof drainage boards. These fabrics are Black Color Geocell designed to be resistant to foreign particle clogging from dirt, gravel, and other debris that might clog the drainage core during installation. They also have sufficient strength and elongation to resist damage during the construction process.

These fabrics are not meant to replace a drainage stone layer in the drainage system, but can be used underneath a stone slab to help improve permeability. The pore size and number of openings in these fabrics is critical for ensuring adequate filtration. For the best results, this material should be matched to the soil grading.

For instance, a needle punched nonwoven would be a good choice to place beneath a stone slab for a French drain or as a layer in a perforated pipe or trench drain system. Woven polypropylene is a robust, high-tensile filtration fabric that can bear heavy loads and tolerate road rut, extend pavement life, and act as a sediment barrier.