Editor's note: The following article was adapted from "Balancing Waterproofing and Thermal Performance for Vegetative Roof Assemblies," which was presented at the International Symposium 2011: Emerging Technologies and Roof System Performance.
Vegetative roof systems, perceived by many as durable, sustainable, energy-efficient and high-performing, comprise layered assemblies combining landscaping, thermal insulation, waterproofing components and other elements to provide a functioning system. But there are different approaches to vegetative roof system installation.
Insulation can be placed above a vegetative roof system's waterproofing membrane to improve waterproofing performance; this often is referred to as an inverted roof membrane assembly. With this construction, water flows through the insulation and compromises the insulation layer's thermal resistance at the membrane level. This often is recognized as an acceptable compromise to improve waterproofing performance. However, the magnitude of the loss in thermal resistance is difficult to quantify and not well-understood.
Inverted roof assemblies