Of all the choices the owner or specifier has to make when designing green roof systems, the choice of waterproofing is easy. The Hyproof membrane is a high-performance Coal Tar Elastomeric Membrane (CTEM). Incorporating the modern benefits of DuPont™ Elvaloy® and the time-proven properties of coal tar pitch, Hyproof has passed the 2-year FLL root barrier test and proved itself a superior waterproofing barrier for green roof systems.
The Hyproof membrane, along with our full line of accessory products, will provide the optimal, long-lasting waterproofing choice for any and all green roof systems.
The structural capacity of the building and roof deck must be able to support the added dead load of the green roof when saturated with water following a rain event. For a simple extensive roof using lightweight media this will be about 7.5 lbs. per square foot of roof per inch of media depth. For intensive roofs with heavier media and larger plants, this could be much greater. Roofs with a slope greater than 2 in 12 may require supports to stabilize the roof system. Insulation, if used, must have sufficient compressive strength that can withstand the dead and live loads.
Drainage is needed to allow excess rainwater to flow off the roof. Drainage can be a coarse granular material or a synthetic layer. Granular drainage may be lightweight aggregate like lava rock, or expanded clay, slate or shale. If the structure can support the weight, gravel or crushed brick or other similar material can be used. Granular drainage layers are typically 2″ thick. Using granular drainage can replace some of the media thickness required. Synthetic drainage sheets will be lighter and are typically 1/2″ thick. Regardless of the type of drainage used, it should always be separated from the media by a filter fabric to prevent fines from the media filling the drainage.
Media selection is critical to the success of a green roof. Considerations include weight, stability, water-holding capacity and hydraulic conductivity. Most lightweight commercial media combine a lightweight aggregate like expanded clay, slate or shale (80-90% by volume) with organic compost (10-20% by volume). For extensive green roofs using commercially available lightweight media, the optimal media depth is 3.5″ to 4.5″. This gives the best balance when considering the necessary structural strength of the building, the cost of media and vegetation, the moisture-holding capacity (stormwater management) and maintenance requirements. If the building can support greater weight, less-costly materials like fine gravel and sand can be used. In either case, the media should be tested and meet FLL guidelines for the type of roof.