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Title
Balancing Waterproofing and Thermal Performance for Vegetative Roof Assemblies
Balancing Waterproofing and Thermal Performance for Vegetative Roof Assemblies
Date
9/2011
9/2011
Author(s)
Matther Nornandeau; Michael Waite
Matther Nornandeau; Michael Waite
Page(s)
Keyword(s)
vegetative roof; green roof; waterproof; insulation; invertred roof; drainage; protected membrane; durability
vegetative roof; green roof; waterproof; insulation; invertred roof; drainage; protected membrane; durability
Abstract
In contrast with traditional roofing practice, many building deck waterproofing systems, including those used in vegetative roof assemblies, place insulation above the waterproofing membrane, in part to improve the system’s waterproofing performance. This assembly often is referred to as an inverted roof assembly. With this construction, water flows down through the insulation and at the membrane level compromises the insulation layer’s thermal resistance. This often is recognized as an acceptable compromise to improved waterproofing performance. The magnitude of the loss in thermal resistance is not well understood and difficult to quantify and, therefore, typically is not compared scientifically to waterproofing performance. This paper discusses the effects when insulation is placed above the membrane on the roof assembly’s waterproofing performance, and presents a thermal model incorporated into a computer energy model to evaluate the effects of water flow through a drainage layer beneath the insulation. We analyze the heat transfer effects of inverted roof assemblies for vegetative systems on building energy use by performing building energy simulations, using weather data for various locations in the U.S. The popularity of vegetative roofing and the perception of these roof systems as sustainable, energyefficient, and high-performing make research of this topic timely.
In contrast with traditional roofing practice, many building deck waterproofing systems, including those used in vegetative roof assemblies, place insulation above the waterproofing membrane, in part to improve the system’s waterproofing performance. This assembly often is referred to as an inverted roof assembly. With this construction, water flows down through the insulation and at the membrane level compromises the insulation layer’s thermal resistance. This often is recognized as an acceptable compromise to improved waterproofing performance. The magnitude of the loss in thermal resistance is not well understood and difficult to quantify and, therefore, typically is not compared scientifically to waterproofing performance. This paper discusses the effects when insulation is placed above the membrane on the roof assembly’s waterproofing performance, and presents a thermal model incorporated into a computer energy model to evaluate the effects of water flow through a drainage layer beneath the insulation. We analyze the heat transfer effects of inverted roof assemblies for vegetative systems on building energy use by performing building energy simulations, using weather data for various locations in the U.S. The popularity of vegetative roofing and the perception of these roof systems as sustainable, energyefficient, and high-performing make research of this topic timely.