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Title
Decision Making Process for Green Options in Reroofing
Decision Making Process for Green Options in Reroofing
Date
9/2011
9/2011
Author(s)
Steven Bentz
Steven Bentz
Page(s)
Keyword(s)
sustainable; green roofing; reroofing; vegetative
sustainable; green roofing; reroofing; vegetative
Abstract
By definition, sustainable roofing systems should be long-lasting, recyclable, and reduce a building’s effect on the environment. Good roofing practice also requires that the roof system be durable and repairable. In many cases, a roof is a staging area for servicing mechanical equipment, window washing, façade access, and maintenance; it must be durable enough to support these functions. Green roofing has placed a few new demands on the roof system: the ability to reduce the energy burden of the building, reduce contributions to the heat island effect, offer storm water retention, and provide new green space. While meeting all of these requirements, a green roof must also be functional and maintain a watertight condition during its expected useful life (EUL). In order to enhance the roof’s contribution to environmental requirements, “green” roofing has evolved in to one of two categories: highly reflective or “cool” roof systems, and vegetative roof systems. To most of the general public, vegetative roof systems have become the default definition of a green roof. Vegetative roof systems have captured the interest of many municipalities as the answer to the need for sustainable roofing, with many tax incentives being based around promoting its use. Both vegetative roof systems and cool roof systems offer challenges when assessing appropriate replacements for existing roof systems. Cool roof systems that rely on a high solar reflectance index (SRI) offer a generally easier path to sustainable roof systems that meet current environmental-based requirements. The challenge of a cool roof system as a reroofing option is to ensure wind-uplift and durability requirements are met with an exposed membrane and meet building code requirements. Repairability of an exposed membrane offers advantages over vegetative roof systems or protected membrane roof assemblies (PMAs). A vegetative roof system is difficult to repair because of the buried nature of the membrane. Additionally, the added weight of a vegetative roof system and PMA can necessitate upgrades to the building structural frame in order to increase structural capacity. The purpose of this paper is to present a practical decision-making process for selection and design of a sustainable or green, reroofing system. The process will consider the various assemblies currently available in the market today, compare the advantages and disadvantages of each, and illustrate which assemblies meet cool roofing and vegetative roofing guidelines. Specific aspects of the roofing systems to be compared will include the following: • wind-uplift resistance • fire rating • thermal resistance • membrane durability and expected life cycle • potential for reusing insulation and insulation durability leak identification and repair methodologies • reduction of heat island effect • Solar Reflectance Index (SRI) • storm water retention • roof top accessibility • roof top use considerations • fall protection, façade access and window washing rigging • mechanical equipment staging • parapet heights and aesthetic effects • structural implications, • social, economical, and environmental effects of each system. It is expected that the reader will take away from this paper a better understanding of “green” roof options that are viable to reroofing.
By definition, sustainable roofing systems should be long-lasting, recyclable, and reduce a building’s effect on the environment. Good roofing practice also requires that the roof system be durable and repairable. In many cases, a roof is a staging area for servicing mechanical equipment, window washing, façade access, and maintenance; it must be durable enough to support these functions. Green roofing has placed a few new demands on the roof system: the ability to reduce the energy burden of the building, reduce contributions to the heat island effect, offer storm water retention, and provide new green space. While meeting all of these requirements, a green roof must also be functional and maintain a watertight condition during its expected useful life (EUL). In order to enhance the roof’s contribution to environmental requirements, “green” roofing has evolved in to one of two categories: highly reflective or “cool” roof systems, and vegetative roof systems. To most of the general public, vegetative roof systems have become the default definition of a green roof. Vegetative roof systems have captured the interest of many municipalities as the answer to the need for sustainable roofing, with many tax incentives being based around promoting its use. Both vegetative roof systems and cool roof systems offer challenges when assessing appropriate replacements for existing roof systems. Cool roof systems that rely on a high solar reflectance index (SRI) offer a generally easier path to sustainable roof systems that meet current environmental-based requirements. The challenge of a cool roof system as a reroofing option is to ensure wind-uplift and durability requirements are met with an exposed membrane and meet building code requirements. Repairability of an exposed membrane offers advantages over vegetative roof systems or protected membrane roof assemblies (PMAs). A vegetative roof system is difficult to repair because of the buried nature of the membrane. Additionally, the added weight of a vegetative roof system and PMA can necessitate upgrades to the building structural frame in order to increase structural capacity. The purpose of this paper is to present a practical decision-making process for selection and design of a sustainable or green, reroofing system. The process will consider the various assemblies currently available in the market today, compare the advantages and disadvantages of each, and illustrate which assemblies meet cool roofing and vegetative roofing guidelines. Specific aspects of the roofing systems to be compared will include the following: • wind-uplift resistance • fire rating • thermal resistance • membrane durability and expected life cycle • potential for reusing insulation and insulation durability leak identification and repair methodologies • reduction of heat island effect • Solar Reflectance Index (SRI) • storm water retention • roof top accessibility • roof top use considerations • fall protection, façade access and window washing rigging • mechanical equipment staging • parapet heights and aesthetic effects • structural implications, • social, economical, and environmental effects of each system. It is expected that the reader will take away from this paper a better understanding of “green” roof options that are viable to reroofing.