Published in the ECHO Journal, July 2009
Roofing products have taken on an important role as the consciousness for the need to improve our environmental conditions increases. These products can help reduce the carbon footprint, reduce dwelling energy requirements, provide a platform for sustainable energy, improve air quality and reduce storm water runoff. To better understand these issues it is important to know some general “green” terminology, what cool roofs are, what is the relationship between solar energy and roofing, what a green roof is and what rebates are available to help offset the costs of environmentally friendly roof systems. The current status of roofing is “Green,” and the future will see it getting greener.
Green Terminology
Some base line “Green” terminology will help provide both background information and clarity for this dissertation on current roofing technology.
Carbon Footprint – The amount of CO2 and other gasses we create through our normal living choices that have a negative effect on the atmosphere.
CFCs – Chlorofluorocarbons are known as all green house gasses that negatively affect the atmosphere.
Alternative Fuels – Fuels generated from renewable resources such as wind and solar.
Sustainability – The ability to meet the needs of today without jeopardizing the needs of tomorrow.
Solar Reflectivity in Roof Products – A product’s ability to reflect solar energy and ultimately reduce the energy requirements needed to cool a dwelling, given in percent.
Thermal Emissivity in Roof Products – The ability of a roof product to emit or radiate back to the atmosphere any absorbed energy, thus reducing the energy requirements to cool a dwelling, given in percent.
Aged Reflectivity – The reflectivity of a roof product after three years from installation, given in percent.
SRI – The Solar Reflective Index is a number used to measure a roof’s operating temperature scaled from 1 to 100 with 100 being the best.
CRRC – The Cool Roof Rating Council is an independent nonprofit group that measures solar reflectance and thermal emissivity in roof products.
LEED – Leadership in Energy and Environmental Design is a voluntary program created by the U.S. Green Building Council to determine a building’s use sustainability and carbon footprint. Building systems are given LEED point credits.
Energy Star – Energy Star is a joint Federal Government program between the Energy Department and the Environmental Protection Agency to establish minimums for solar reflectance and thermal emissivity, as well as other energy related items.
Title 24 California Energy Code – The California code establishes building energy efficiency standards for residential and non residential buildings.
In 2006 Title 24 established energy code requirements for low-sloped (< 2:12) roofs on commercial buildings and high-rise residential (> four stories). The term “Cool Roof” although already in use became a requirement at this time. A cool roof for low-sloped applications is defined as one with initial reflectance of 70%, an emissivity of 75%, an aged reflectance of 55%, and an SRI of 64.
Cool roof products must be tested by the CRRC and meet the requirements of Title 24. The most commonly used low-sloped cool roofs are: 1) PVC (polyvinyl chloride) and TPO (thermoplastic olefin) single ply membranes, 2) Fluid applied membranes, and 3) built-up asphalt cool roofs. All of these systems are readily available in the market place and will vary in cost for material and installation.
Single Ply Roof System
The single ply systems are typically white thermoplastic reinforced membranes. They are most commonly attached to the roof deck with plates and screws at the seam edge and the overlapping seam is heat welded providing a cohesive attachment. There are occasions where the membrane is fully adhered to the substrate. The membrane can be applied over an existing roof or applied over a fire barrier after the old roof is removed. The single plies have gained in popularity as a result of the cool roof requirements and the recent increased cost of asphalt products.
Fluid Applied Roof System
Fluid applied membranes are typically acrylic or elastomeric coatings that are installed over an existing roof, typically a cap sheet built-up roof system. They consist of a primer, a base coat and a white top coat, which accommodate the cool roof requirements. A polyester reinforced fabric can be embedded into the system to provide greater tensile strength. The coating systems can be a cost effective alternative for extending the life of a current roof system and fulfill the cool roof requirements.
Built-Up Cool Roof
Asphalt built up roofing (BUR) manufacturers have created a cap sheet product which qualifies as a cool roof. The granulated cap sheet is coated with a white roof coating at the plant, prior to shipping. Once installed, the asphalt roof is white and if CRRC tested and Title 24 approved qualifies as a cool roof. These BUR systems are still popular today in spite of the increase in asphalt prices; however, the single plies and fluid applied systems are gaining market share.
Beginning August 1, 2009, Title 24 requirements apply for all low-sloped roofs, both non-residential and residential. Additionally, new requirements for steep-sloped (>2:12) roofing will be added. For roofing material weighing less than five pounds per square foot (typically composition shingles), Title 24 requires a 75% emissivity, an aged reflectance of 20% and an SRI of 16. For product weighing greater than or equal to five pounds per square foot (typically tile), Title 24 requires a 75% emissivity, an aged reflectance of 15% with an SRI of 10.
Many of the composition shingle manufacturers have created new products that meet the new Title 24 requirements, without limiting their colors only to white. They have been able to coat the granules with a reflective product prior to adding the color coat, thus achieving the cool roof requirements. Additionally, some tile manufacturers have created similar technology to allow their products to qualify as well. These products still must pass the testing of the CRRC and achieve the minimum standards set by the energy code.
The California Energy Commission has broken our state into climate zones. These zones will dictate Title 24 requirements for roofing products, particularly the new steep-slope products. The Bay Area and most of the central coast are in zone three and are exempt from the new Title 24 codes as they relate to steep slope roofing. However, tax credits as well as other rebates may be available to owners if they choose to install one of these steep slope cool roofs.
Solar Panels
Solar panels have been in use for many, many years. Their early use was primarily to heat water either for swimming pools or domestic use as a way of reducing energy consumption. Today, the popularity of photovoltaic solar panels to generate energy is rapidly increasing. A photovoltaic cell is defined as the ability to generate current or voltage from radiant energy. Most cells capture about 10 to 15 percent of the sun’s energy. New technology states up to 30 percent can be captured. With today’s technology and costs it takes about ten years to return the installation investment.
Photovoltaic cells and roofing are often mentioned concurrently because it is common to place panels on the roof. Additionally, some tile and single ply membrane manufacturers have incorporated photovoltaic cells into their roofing products. When considering solar panel placement on a roof, it is imperative that the mount design is compatible with the particular type of roof you have, is engineered properly to withstand the weight without damaging the structure or the roof and takes into consideration both the necessary waterproofing and ease of re-roof.
Green Roofs
“Green” or garden roofs have been popular in Europe for some time. More recently green roofs have become popular in North America. A green roof consists of a waterproof membrane, a root barrier, drainage mat, the growing medium, irrigation system and the vegetation. The benefits of these systems include year round energy savings as the vegetation acts as a thermal blanket and minimizes heating and cooling needs, drastically reduces water run off (up to 70%), reduces the ambient air temperature, helps reduce CO2 pollution through the photosynthetic process of the vegetation, extends the life of the roof membrane by protecting the system from damaging UV radiation, and provides for up to 14 LEED credit points.
It is popular to combine many of these energy saving roof systems to maximize sustainability and reduce future costs such as installing photovoltaic panels on a green roof or incorporating photovoltaic tiles on a cool tile roof. Most of these systems, whether stand alone or combined, may qualify for some form of rebate.
Rebate and Tax Credit Programs
There are many rebate and tax credit programs available for energy saving roof systems. For instance, although we are in a state designated climate zone that does not require cool residential roofs, federal tax credits are still available which may or may not make it cost effective to install. Utility companies such as PG&E provide rebates for cool roofs as well as other roof related items such as insulation and mechanical and solar equipment. There are state and local rebate programs for photovoltaic energy that are too numerous for this article. Solicit your construction experts to help in compiling the programs available for your needs. The following list of websites provide information resources for tax credits and rebates related to saving energy:
- roofknowledge.org
- dsireusa.org
- energy.ca.gov
- coolroofs.org
- PGE.com
Brian Seifert heads the Roofing Division at Draeger. He is the chair and long-time member of the ECHO Maintenance Resource Panel. He is also a frequent contributor to the ECHO Journal and speaker at ECHO seminars.