Environmental Design + Construction - October 2008 - (Page 28) Cool Roofing additional insulation should be included in the design knowing the in-place R-value will be reduced when the insulation contains some amount of water. NRCA recommends a waterproofing membrane be used for green roofs, and that it be adhered to the substrate. NRCA believes this is the most appropriate method to ensure a long service life for a green roof system waterproofing membrane. Even though a green roof uses a waterproofing membrane, there should be positive drainage. Positive drainage should be provided by sloping the deck. Anticipating localized deflection will help ensure positive drainage. Perhaps additional structural suppor t is required to prevent localized deflection. Insulation is installed above the membrane. Insulation should have high compressive strength — adequate to suppor t the weight of all components and the expected live load — and be resistant to deterioration from moisture. Many of the traditional waterproofing membranes are used with green roofs. NRCA recommends five membrane types for green roof systems: 28 Cool Roofing • Hot-fluid-applied polymer-modified asphalt membrane. • APP- and SBS-polymer-modified bitumen sheet membrane. • EPDM membrane. • PVC membrane. • One- and two-component, fluid-applied elastomeric membrane. Installation guidelines and construction details for each membrane type are provided in The NRCA Green Roof Systems Manual–2007 Edition. DESIGN CONSIDERATIONS There are many other design considerations to bear in mind when designing a green roof system. Membrane flashing details should terminate at or above the top surface of the growth medium. Membrane flashings and counterflashings below the top of the growth medium are more susceptible to leakage and are more difficult to maintain. With that in mind, NRCA’s green roof construction details include access to the flashings at perimeters and interior penetrations. Installing pavers or gravel along the flashings > Fall 2008
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.