Waterproof Membranes
Waterproofing is fundamental in a successful green roof design. When retrofitting an existing building with a green roof, an audit of the existing membrane must be undertaken by a qualified professional. Usually the green roof application will trigger the installation of a new membrane that meets green roof specifications.
There are several choices of waterproof membranes.
- Thermoplastic membranes, such as PVC (polyvinyl chloride) or TPO (thermal polyolefin) using hot air infusion
methods are commonly used.
- Elastomeric membranes like EPDM (ethylene-propylene rubber materials) have high tensile strength and are well-suited to large roof surfaces with fewer roof Modified bitumen sheets are usually applied in two layers and are commonly available.
- Liquid-applied membranes are generally applied in two liquid layers with reinforcement in The quality is variable.
Membrane types used on green roofs are:
- Liquid- applied
- Single-ply sheet membrane (specifically designed for green roofs)
- Built up layer system consisting of 3+ layers
Waterproof Membranes (continued)
A factor in choosing a waterproofing system is its’ resistance to root penetration. Protection of the waterproof membrane should be provided by either adding a root barrier or using a membrane that is resistant to penetration (more cost efficient). (Van. SSCDG.
2005.)
Some membranes (usually bitumen or organic materials) are susceptible to root penetration and micro-organic activity and need to be separated from the growing medium by a continuous root barrier unless they contain an adequate root repelling chemical or copper foil. (Ngan, 2003.)
Chemically incompatible materials such as bitumen and PVC require a separation layer. (FLL, 2002).
When the installation is complete, the waterproof membrane should be tested by flooding and inspection. On advice, an electronic leak detection system may be installed under the membrane. In best practice, a building professional will identify the areas that re- quire waterproofing, recommend the appropriate systems and products and provide technical specifications. (Van. SSCDG. 2005)
