Above Sheathing Ventilation will be an integral part of next generation roofing. For a wealth of information on the subject visit abovesheathingventilation.com

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4. Natural convective air flow develops in an air space
created between a roof product and the roof
sheathing
Buoyancy forces from heated air create a flow from
eave to ridge
Air flow dissipates heat build-up and reduces heat
gain through the roof sheathing when compared to
direct nailed roof products with no air space
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Offset mounting
Batten and counter batten sub-
framing is common practice for
some roof products
Continuous air space is created
from eave to ridge
Profiled roofing products create
space above the deck
Special sandwiched sheathing
products are available with
space designed into them
Batten/Counter-Batten Frame
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Natural airspace along
with air permeability of
installed tiles promotes
air flow beneath and
around tiles.
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Roof Coatings Manufacturers Association
Tile Roofing Institute
Cool Metal Roofing Coalition
CEC PIER IRR Pigment Project
DOE, MCA and Stone Coated Metal Mfrs.
Renegade Roof Systems, Poly Foam Corp., Tile
Roofing Institute, Louisiana Pacific
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Various types of tile roofing (2001) and metal roofing
(2003)
Control: direct nailed asphalt shingle
Measurements of temperature, heat flux, weather
conditions, solar reflectance and thermal emittance
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Formulate and Validate AtticSim for Cool Color and Above-Sheathing Ventilation
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(a) As air temperature under the roof surface increases, heated air rises
toward the ridge and draws cooler air into the system through vented eave.
(b) Heated air exhausts through the vented ridge assembly. High profile
roofing products allow more heated air to exhaust through ridge vent.
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Tile, slate, metal shingles Plan view of the roof showing air flows between tiles and underlayment
Eave
are air permeable
Wind direction
Permeability 0.5-1.0% of the
laid area Ridge
Complicated flow
networks Eave
Flow influences:
Outward acting pressures
Energy performance over leeward slope
Streamlined
Wind loading flow
Driving rain performance Separated wake
(very unstable)
Batten space flows
Dispersion of moisture Area of separated
Flow near eaves
Lafarge Roofing Technical Center
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14. Control - Asphalt Shingle (SR093E89)
Shake Dark Gray (SR08E90) Batten and Counterbatten
Shake Light Gray (SR26E90) Batten-Counterbatten
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Heat Flux through Roof Deck
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[Btu/(hr · ft2)]
30%Drop
20 45%Drop
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0
-10
0
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84 24
96 12
108 24
120 12
132 24
144
Time into Week (hrs)
ASV results in a 30% drop in heat gain compared to asphalt shingle. A cool
(IR reflective) surface adds an additional 15% to reduction in heat gain. 14

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R 38 Attic Insulation with AC ducts insulated to R-6
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The lower the solar reflectance of the roof, the more ventilated
heat exits the ridge vent
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Reduced moisture content in OSB is well
below content without a vented cavity
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Empirical algorithm captures energy benefits of Above Sheathing Ventilation
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Reflectance of 0.25; Emittance of 0.90
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22. Light Gray Shake, (SR246E90)
Underside Unpainted
Batten & Counter batten
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Field Testing at FSEC (1994)
Tile roofing, variety of venting designs
Temperature and heat flux measurements
45-50% reduction in heat gain vs. dark shingle direct
nailed
Research at Lafarge Technical Center (UK)
Predicted ORNL field data on clay tile
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2008 CA Building Energy Efficiency Standards
(Title 24) 45-day language as equivalence option to
cool roofing
Passive cooling section in Energy Efficiency
Category of NAHB Green Building Standard
(under development)
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26. US Department of Energy
Energy Efficiency and Renewable Energy
Roof Material
Foil backed OSB
Upper
air channel
Radiant
barriers PCMs
Upper
air channel
Lower air
channel
Insulation w/ foil
Gypsum board
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Full System
Integration
90% reduction
in peak demand
PCM Shaves Peak
Demand
and Reduces Night
Sky Losses
July 28, 2006 27

28. Above Sheathing Ventilation alone causes a 30-50%
reduction in heat gain, compared to dark asphalt
shingle direct-to-deck
Range from metal vs. tile roofing
Reduction in heat gain is equivalent to 15 points of
solar reflectance
Combining ASV with cool surfaces reduces the heat
gain even more
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