ASV (Above Sheathing Ventilation)
A Radiant ASV Cool Roof complies with Title 24 California Building Standards, Section 152, and NAHB Green Building Standard, Chapter 7, which both state that roofs installed with an appropriate air gap are considered equivalent to the prescriptive definition of a cool roof (i.e cool pigment roofs)- regardless of the roof color and it's associated solar reflectance.
See: California energy commision cec title24-policy letter
ASV Studies on the Effects of ASV on Stone-Coated Metal Roofs - The Field Test Results
Miller, Wilson, and Karagiozis (2006) field tested stone coated metal roofs on adjacent attic test assemblies very similar to the assemblies used for testing tile.
A commercially available asphalt shingle with a solar reflectance of 0.093 and a thermal emittance of 0.89 (SR093E89) was selected as the control for comparing the thermal performance of the metal roof systems. A conventional dark-gray stone-coated metal shake (SR08E90) and a light-gray shake (SR26E90) were tested on identical batten and counter-batten constructions.
All attic assemblies were equipped with 1 ft2 of soffit and ridge ventilation per 300 ft2 of attic footprint for supporting attic ventilation. Miller, Wilson, and Karagiozis (2006) observed that venting the underside of the dark-gray stone-coated metal shake significantly reduced the heat flow crossing the deck during solar noon.
The dark-gray stone-coated metal shake and the asphalt shingle have almost identical reflectance and emittance characteristics, yet the heat flow crossing the roof deck of the dark-gray shake is just 70% of the heat flow crossing the roof deck of the asphalt control shingle. The 30% reduction in heat flow is due to ASV.
Miller, Wilson, and Karagiozis (2006) concluded that ventilating the deck is just as important as is increasing solar reflectance and may be the stronger player in reducing heat gain into the attic.
Source http://www.ornl.gov/sci/roofs+walls/staff/papers/19.pdf
A commercially available asphalt shingle with a solar reflectance of 0.093 and a thermal emittance of 0.89 (SR093E89) was selected as the control for comparing the thermal performance of the metal roof systems. A conventional dark-gray stone-coated metal shake (SR08E90) and a light-gray shake (SR26E90) were tested on identical batten and counter-batten constructions.
All attic assemblies were equipped with 1 ft2 of soffit and ridge ventilation per 300 ft2 of attic footprint for supporting attic ventilation. Miller, Wilson, and Karagiozis (2006) observed that venting the underside of the dark-gray stone-coated metal shake significantly reduced the heat flow crossing the deck during solar noon.
The dark-gray stone-coated metal shake and the asphalt shingle have almost identical reflectance and emittance characteristics, yet the heat flow crossing the roof deck of the dark-gray shake is just 70% of the heat flow crossing the roof deck of the asphalt control shingle. The 30% reduction in heat flow is due to ASV.
Miller, Wilson, and Karagiozis (2006) concluded that ventilating the deck is just as important as is increasing solar reflectance and may be the stronger player in reducing heat gain into the attic.
Source http://www.ornl.gov/sci/roofs+walls/staff/papers/19.pdf
US. Dept. of Energy (D.O.E. ) Identifies ASV in 'Next Generation' Thermally Efficient Roofing.
FACT- The D.O.E. Roofing Summit in 2009 identified that 'next generation' thermally efficient roofing would incorporate ABOVE DECK VENTILATION and REFLECTIVE/EMISSIVE COATINGS.
(ref. Page 19 of the D.O.E. Study in Slideshare presentation below )
Socio-Political & Technological Environment Supporting Cool Roof Initiatives
The Socio Political and Technological focus on Energy Savings in North America is intense. Canada lags behind the USA in this regard, this clearly illustrated by the fact that the Energy Star Program in Canada does not include rebates for Cool Roofing.
US Federal Government Support is at unprecedented levels and supports innovative new technologies that focus on saving Energy.
1) Why Cool Roof Energy Saving Benefits are Important?
2) Global Warming and the Macro Economic Outlook for Cool Roofing Products
2.1) Federal Stimulus Support
Provisions include:
· $5 billion to weatherize homes of up to 1 million low-income people.
· $11 billion toward smart-grid technologies to run the power grid more efficiently.
· $13.9 billion in loans to subsidize renewable-energy projects and transmission.
· $6.3 billion in state energy-efficient and clean-energy grants.
· $4.5 billion to make federal buildings more energy efficient.
2.2) Property Assessed Clean Energy (PACE Financing)
FACT - PACE financing, or property assessed clean energy financing, gives property owners the chance to make renewable energy and/or energy efficiency retrofits without any upfront costs. In participating municipalities in 16 US states, homeowners can qualify for a PACE bond which allows them to pay off the costs of retrofits through their property taxes over a 15 or 20 year period.
FACT- The Property Assessed Clean Energy initiative is in the first step in the legislative process to become a national program throughout the USA. Introduced bills and resolutions first go to committees that deliberate, investigate, and revise them before they go to general debate.
FACT- The PACE bond market has the potential to dramatically accelerate the energy retrofitting of America’s building stock by improving affordability.
FACT- “ The PACE Assessment Protection Act of 2010 ” if passed will unlock investment in clean energy and create jobs, and ensure that the underwriting standards of Fannie Mae and Freddie Mac facilitate the use of property assessed clean energy programs to finance the installation of renewable energy and energy efficiency improvements.
FACT - PACE bonds can be issued by municipal financing districts or finance companies and the proceeds can be typically used to retrofit both commercial and residential properties.
Reference: Letter from Congress to President Obama in Support of PACE July2010
2.3) Cool Roof Ratings Council
The Cool Roof Rating Council (CRRC) is an independent, non-profit organization that maintains an unbiased rating system for radiative properties of roof surfacing materials.
FACT- Since roofs are seen as the main culprit in energy loss, a new Cool Roof Rating Council has been formed to monitor, advise, and test emissions.
FACT- In hot or cold climates, ‘energy-leak’ roofs are contributing to escalating concerns. According to the CRRC, a cool roof can reduce cooling energy costs by up to 15 percent in most climate zones worldwide and reduce heating costs in winter when used in conjunction with Above Sheathing Ventilation.
2.4) Urban Heat Islands
Ross Mc Kitrick, an economics professor at the University of Guelph in Ontario, Canada, and Patrick Michaels, an environmental studies professor at the University of Virginia and Senior Fellow at CATO, published research urban heat islands, asserting that half the global warming trend from 1980 to 2002 was caused by non climatic effects, pointing to man made causes such as Urban Heat Islands.
FACT- Unlike global warming, which affects worldwide temperatures, heat islands are localized.
FACT- According to the U.S. Environmental Protection Agency (EPA), many urban areas are up to 10 degrees Fahrenheit warmer.
FACT- Along with waste heat from vehicles, factories, and AC, heat islands form as natural land cover is removed, deleting the cooling effects of shading and water evaporation, and tall buildings and narrow streets heat the air trapped between them.
FACT - The increased use of AC results in the release of more of the heat-trapping greenhouse gases that cause global warming.
FACT -The Heat Island Group, a research and advocacy organization, estimates that Los Angeles, California spends about $100 million per year in extra energy costs to offset its heat island effect.
A Cool Communities program, supported by American Forests and the U.S. Department of Energy, encourages building owners and policymakers to adopt plantings, ‘green’ roofs and light-colored surfaces.
2.5) Above Sheathing Ventilation (ASV)–The Proven Cool Roof Strategy for Tiled Roofs
FACT- Placing concrete tiles and stone-coated metal roofs on batten and counter-battens provides excellent thermal performance, although it is not the current practice used in Florida or in California because of concerns about wind uplift during storms. Counter-batten construction provides an air space between the exterior face of the roof sheathing and the underside of the roof cover so that a clear, albeit complex, air pathway exists beneath the roof cover from the soffit to the ridge of the roof. Solar irradiance absorbed at the roof’s surface is conducted through the roof and convected as heat to the air.
The warmer – and therefore, more buoyant – air moves up the inclined air passage. Miller, Wilson, and Karagiozis (2006) observed that the ventilation scheme helped remove unwanted heat and moisture from the roof deck, thereby improving the
roof’s thermal performance as well as its durability. The thermally induced airflow occurring in this air space is termed above-sheathing ventilation (ASV).
US Federal Government Support is at unprecedented levels and supports innovative new technologies that focus on saving Energy.
1) Why Cool Roof Energy Saving Benefits are Important?
- FACT- The US primary energy consumption is expected to grow 1.1% annually
- Source: Energy Information Administration (EIA http://www.eia.doe.gov/ )
- FACT- By 2030 US electricity demands will be 45% greater than today
Source: Nuclear Energy Institute (NEI http://www.nei.org/ ) - FACT- The level of oil imports will remain between 53% and 68% of total oil usage through 2030
Source: Energy Information Administration (EIA http://www.eia.doe.gov/ )
- FACT- "The cheapest, most reliable source of new energy is saved energy.
Source: Energy – Peter Turnbull PG&E (Pacific Gas and Electricity http://www.pge.com/ )
2) Global Warming and the Macro Economic Outlook for Cool Roofing Products
2.1) Federal Stimulus Support
- Cool roofing significantly addresses the issue of global warming, while growing the economy, creating new jobs, and promoting the development of new technologies.
- As weather conditions around the world place greater demands on architectural structures and eco-awareness evolves, business and government are seeking viable and innovative approaches to conserving resources, both natural and economic.
- As a result of a new economic stimulus package, homeowners who make energy efficient updates to their home, including the installation of a painted or coated Energy Star® labeled metal roof, may be eligible for a tax credit worth 30% of the material costs, up to $1,500 per home. To qualify, the metal roof must be installed between January 1, 2009 and December 31, 2010.
- The American Recovery and Reinvestment Act of 2009 provides $50 billion (of a total $790 Billion) for energy programs, much of it focused on energy efficiency and renewable energy, and $20 billion in tax incentives for renewable energy and efficiency, according to a conference report released by House Speaker Nancy Pelosi's office (
Provisions include:
· $5 billion to weatherize homes of up to 1 million low-income people.
· $11 billion toward smart-grid technologies to run the power grid more efficiently.
· $13.9 billion in loans to subsidize renewable-energy projects and transmission.
· $6.3 billion in state energy-efficient and clean-energy grants.
· $4.5 billion to make federal buildings more energy efficient.
2.2) Property Assessed Clean Energy (PACE Financing)
FACT - PACE financing, or property assessed clean energy financing, gives property owners the chance to make renewable energy and/or energy efficiency retrofits without any upfront costs. In participating municipalities in 16 US states, homeowners can qualify for a PACE bond which allows them to pay off the costs of retrofits through their property taxes over a 15 or 20 year period.
FACT- The Property Assessed Clean Energy initiative is in the first step in the legislative process to become a national program throughout the USA. Introduced bills and resolutions first go to committees that deliberate, investigate, and revise them before they go to general debate.
FACT- The PACE bond market has the potential to dramatically accelerate the energy retrofitting of America’s building stock by improving affordability.
FACT- “ The PACE Assessment Protection Act of 2010 ” if passed will unlock investment in clean energy and create jobs, and ensure that the underwriting standards of Fannie Mae and Freddie Mac facilitate the use of property assessed clean energy programs to finance the installation of renewable energy and energy efficiency improvements.
FACT - PACE bonds can be issued by municipal financing districts or finance companies and the proceeds can be typically used to retrofit both commercial and residential properties.
Reference: Letter from Congress to President Obama in Support of PACE July2010
2.3) Cool Roof Ratings Council
The Cool Roof Rating Council (CRRC) is an independent, non-profit organization that maintains an unbiased rating system for radiative properties of roof surfacing materials.
FACT- Since roofs are seen as the main culprit in energy loss, a new Cool Roof Rating Council has been formed to monitor, advise, and test emissions.
FACT- In hot or cold climates, ‘energy-leak’ roofs are contributing to escalating concerns. According to the CRRC, a cool roof can reduce cooling energy costs by up to 15 percent in most climate zones worldwide and reduce heating costs in winter when used in conjunction with Above Sheathing Ventilation.
2.4) Urban Heat Islands
Ross Mc Kitrick, an economics professor at the University of Guelph in Ontario, Canada, and Patrick Michaels, an environmental studies professor at the University of Virginia and Senior Fellow at CATO, published research urban heat islands, asserting that half the global warming trend from 1980 to 2002 was caused by non climatic effects, pointing to man made causes such as Urban Heat Islands.
FACT- Unlike global warming, which affects worldwide temperatures, heat islands are localized.
FACT- According to the U.S. Environmental Protection Agency (EPA), many urban areas are up to 10 degrees Fahrenheit warmer.
FACT- Along with waste heat from vehicles, factories, and AC, heat islands form as natural land cover is removed, deleting the cooling effects of shading and water evaporation, and tall buildings and narrow streets heat the air trapped between them.
FACT - The increased use of AC results in the release of more of the heat-trapping greenhouse gases that cause global warming.
FACT -The Heat Island Group, a research and advocacy organization, estimates that Los Angeles, California spends about $100 million per year in extra energy costs to offset its heat island effect.
A Cool Communities program, supported by American Forests and the U.S. Department of Energy, encourages building owners and policymakers to adopt plantings, ‘green’ roofs and light-colored surfaces.
2.5) Above Sheathing Ventilation (ASV)–The Proven Cool Roof Strategy for Tiled Roofs
FACT- Placing concrete tiles and stone-coated metal roofs on batten and counter-battens provides excellent thermal performance, although it is not the current practice used in Florida or in California because of concerns about wind uplift during storms. Counter-batten construction provides an air space between the exterior face of the roof sheathing and the underside of the roof cover so that a clear, albeit complex, air pathway exists beneath the roof cover from the soffit to the ridge of the roof. Solar irradiance absorbed at the roof’s surface is conducted through the roof and convected as heat to the air.
The warmer – and therefore, more buoyant – air moves up the inclined air passage. Miller, Wilson, and Karagiozis (2006) observed that the ventilation scheme helped remove unwanted heat and moisture from the roof deck, thereby improving the
roof’s thermal performance as well as its durability. The thermally induced airflow occurring in this air space is termed above-sheathing ventilation (ASV).
