Green Roof Drainage Board

Effective water management is crucial to green roof health and longevity. A well-functioning drainage layer prevents issues like waterlogging and soil erosion that can compromise the stability of a green roof.

It also ensures that plants receive adequate water during dry periods. But the design of green roof drainage boards varies significantly.

Adaptability

Green roof drainage boards provide a water reservoir to supply plant growth media with a constant source of water during rain events. They are available in a range of sizes and shapes, and can be easily integrated into a green roof build-up. They are ideal for use on flat roofs where a traditional green roof is not feasible. They are also compatible with a variety of waterproofing membranes, including liquid-applied systems, single-ply sheet membranes, and built-up roof systems.

Unlike soils, green roof growing medium has limited water-holding capacity and requires regular overhead irrigation to keep plants well-hydrated during the establishment phase. This is especially true for intensive green roofs, which require a larger number of planting plugs or seeds to establish a dense vegetative cover.

The key to green roofing drainage is the combination of a porous growing medium and a water-permeable, lightweight protection layer. This layer must be capable of resisting strains induced by point loads and puncture from sharp protective elements such as root-barriers and spikes. It must also be able to withstand compression from the weight of plant material and from extreme loading.

A green roof drainage board enables the growth of plants that are adapted to the urban environment. Moreover, they help reduce the volume of stormwater runoff, thus lowering the amount of contaminants carried by the water. This helps improve air quality and reduce the amount of energy required for water management.

Energy efficiency

Green roofs offer many environmental and economic benefits, but proper drainage is essential to their longevity. When the drainage system is designed well, it can help to keep excess water from accumulating on the roof and reduce energy demands. Moreover, it can also help to lower the ambient temperature in the building and prevent ice buildup during colder weather.

A good drainage system can help to prevent problems like root rot and erosion. However, it is crucial that it be able to absorb large quantities of water during a storm event. If this is not possible, then the drainage system should be able to redirect water to a roof drain.

To ensure that excess water is drained quickly and efficiently, a drainage system should use a material with high transmissivity. This can be Green roof drainage board achieved by using a filter geotextile or a perforated pipe. The system should also have a reservoir layer and a granular draining/capillary storage mat.

The ArchiGreen SedumDrain 25 is a black water reservoir and multi-directional runoff-delay drainage board made from recycled high impact polystyrene. It has precise 2 mm perforations on the centre of the studs that compose its top surface, known as diffusion openings. These are distributed evenly, so that the studs form small drainage channels that allow the rainwater to spread out. This allows for rapid drainage, preventing water from being pushed into the surrounding vegetation and allowing it to attenuate stormwater runoff.

Water retention

The drainage layer is the backbone of green roofs. It ensures the proper movement of water in a green roof assembly, and it supports the aeration of plant roots while decreasing the volume of stormwater runoff that floods sewer systems and damages buildings.

This layer is also responsible for storing rainwater and irrigating plants during dry periods. As such, a drainage layer must not only be highly permeable but must also hold a substantial amount of water to meet the demands of a green roof’s ecosystem.

To meet this need, green roof drainage boards are designed to retain and discharge a high volume of rainwater, even under load. They have a strong compressive strength and can support the weight of heavy vegetation without clogging.

In addition, the filtration layer around the drainage mat prevents the penetration of fine particles and protects the roof membrane from damage. The drainage board’s geocomposite filter material is an effective permeability barrier that allows green roofs to breathe while protecting the waterproofing system.

For example, the ArchiGreen SedumDrain 25 drainage board is a black, heavy-duty water storage and runoff delay layer made of recycled high impact polystyrene (HIPS) for intensive and semi-intensive green roofs or paved surfaces subject to vehicle traffic. It is thermoformed on both Green roof drainage board sides and features precise 2 mm holes, known as diffusion openings, covering its top surface.

Maintenance

Green roofs are often marketed as ‘low-maintenance’. However, this is not entirely accurate. While they are a great way to enhance a building’s aesthetics, they still require some level of maintenance from time to time. The maintenance needs of a green roof are similar to those of any other garden. They should be weeded regularly, fertilized, and checked for water levels.

One of the most important components of a green roof is a drainage layer that is designed to capture and hold excess stormwater. This helps to prevent excessive puddling or pooling, which can damage the plants and lead to a collapsed green roof. It is also important to check for leaks and repair any areas that are damaged or leaking.

The drainage layer is usually comprised of a mixture of soil and coir or a proprietary green roof growing medium. In some cases, the growing medium is sifted to remove large chunks of organic material, which can interfere with plant growth. This is a crucial step in preventing the growth of unwanted invasive species.

Once the planting is established, a sedum roof should be fertilized annually to insure optimal health and vigour. A granular fertilizer is recommended for the first year of a new green roof. In the spring, a sedum roof should be weeded and trimmed. Invasive weeds and unwanted seedlings can be carried to the green roof by birds and wind, so it is important to carefully inspect for these during maintenance visits.