G-SKY | Planning | Roof Membrane

There is an efficiency threshold that waterproof membranes must meet to qualify for the installation of a Green Roof above them. Waterproofing, durability, environmental friendliness, tensile strength and root resistance qualities are the most important characteristics of the membrane. Once a waterproof membrane has a Green Roof installed on top of it, the cost and time involved to inspect and repair the membrane significantly increases. However, if a durable roof membrane is selected, then adding the Green Roof will extend the life of the waterproof membrane and significantly reduce the life cycle costs of the roof. With a wide installation base and a long reliable service record, asphalt-base (bituminous) and PVC membranes are best suited for Green Roof installations.

	Dur- ability	Water- tight- ness	Tensile Strength	Root Resist- ance	Environ- mental Friendli- ness
Asphalt (Bituminous) Membranes Sheet or Liquid-applied, Seamed	20~60 Years					Long durable service life, high tensile strength and superior watertightness. No resistance to roots, Root Guard must be added.
Thermoplastic Membranes PVC, TPO, Single-ply, Sheet-applied, Seamed	10~20 Years					Good wear resistance, often used on roofs with foot traffic. No additional root protection needed with non-invasive plant species.
Thermoset Membranes EPDM, Single-ply, Sheet-applied, Seamed	10~15 Years					Lightweight and flexible, good for roofs that will not see any foot traffic.
SPF Membranes Sprayed Polyurethane Foam, Liquid-applied, Seamless	10~13 Years					Easy-to-install seamless membrane. Cannot withstand continuously damp conditions.
FRP Membranes Fibreglass-reinforced plastic, Liquid-applied, Seamless	10~15 Years					Quick installation. Can easily crack if shifted by tremors, earthquakes or settling.

Professional Remarks from the 2nd Waterproofing Symposium in Osaka, Japan, June 2003. Courtesy of the Architectural Institute of Japan, from pages 226 and 228.
Checking and repairing leaks in the waterproof membrane after a roof garden is installed is difficult. Therefore, a long term trusted waterproof membrane system must be designed that will not require detailed inspection or general repair in order to maintain its waterproofing ability.	a) Intensive Green Roofs When planting a garden or vegetable-garden, where there will be deep soil with trees, it should be assumed that inspection of the waterproof membrane will be impossible after the garden is installed. Therefore, it is necessary to design the roof with a waterproof membrane that has the durability and service life of at least 50 years.	a) Extensive Green Roofs The trend of installing thin inaccessible green roofs is increasing. On these shallow soil depth green roofs, leaks can occur, but repair is still possible. Given that, a standard roofing membrane with a durability of 20 years should be installed.

Shovels, scissors, cutters and other sharp objects are used to construct and maintain a Green Roof. Occasionally (even when being careful) these tools can be dropped or used with excessive force resulting in physical damage to the roof membrane. Therefore, before any construction on a Green Roof begins, a protective layer should be installed on top of the waterproof membrane to protect it against physical damage.	Concrete Protection Layer Frequently accessed roofs often employ concrete pavers or poured concrete to protect a membrane. 60~80mm thick concrete is poured above the roof insulation. A flexible expansion joint is located at least every 3m.	GR Protection Board Easy adhesion makes this a good choice for vertical applications. A hollow core corrugated polypropylene board. ~6mm thick, flexible, lightweight, easily cut or folded. Less than 6mm thick inhibits waterflow.
Asphalt Barrister ~6mm thick board of formed asphalt. Comes in sheets 500 x 1000mm. Can be used as a temporary protection layer against lightweight equipment such as a bobcat.	GR Mat A recycled fabric mat that can handle extended exposure to the elements outdoors. Very lightweight and thin.	Mortar Approximately 20 to 30 mm at the time of placement, compacts over time. Can crack easily over time.

Mopped-down or Torch-down / Rolled Roofing
(continuous waterproof layer with several layers of redundancy)

Mopped or torched-down membranes are continuously pasted together over multiple layers creating a highly reliable waterproofing system.

Liquid-applied Seamless Roofing
(extremely strong against physical damage)

Fibreglass membranes form a hard shell over the building similiar to the shell of a fibreglass boat. Liquid application is much more difficult and requires special knowledge, care must be taken to ensure a continuous thickness throughout.

PVC or TPO Heat-Welded Seams
(heat-welded seams of like plastics that are stronger than the material)

Sheets of the strong plastic sheet are often custom made in very wide rolls to reduce the number of seams. They are stretched over the roof to create a waterproof layer.