WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA wscarborough@hbig 214.491.7385
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Transcript of WALTER SCARBOROUGH CSI CCS CCCA SCIP AIA wscarborough@hbig 214.491.7385
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WALTER SCARBOROUGHCSI CCS CCCA SCIP [email protected]
D+D Specifiers Series
Sponsored by
Air Barriers
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To provide a “big picture” overview of air barriers
Webinar Intentions
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The Debate is Over
Airtightness is essential to high performance building enclosures …
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… and air barriers fulfill this critical function
The Debate is Over
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• Genesis of discovery in study of vapor barriers
• Canadians have led the way in research about vapor barriers because of severe winters
Discovery of Air Barriers
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• Vapor diffusion through materials was less than infiltration of moisture-laden air through openings in the building enclosure
Discovery of Air Barriers
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• Under controlled conditions, 4’ by 8’ sheet of gypsum board
• Vapor diffusion through board yields 1/3 quart of water
• Moisture-laden air through 1” square hole yields 30 quarts of water
Classic Experiment
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“a system of building assemblies within the building enclosure - designed, installed, and integrated in such a manner as to stop the uncontrolled flow of air into and out of the building enclosure.”
Air Barrier Defined
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Air barriers can also function as a barrier to liquid water infiltration, while allowing water vapor diffusion
An Additional Function
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Thermal imaging of air infiltration at base
Lack of Air Barriers
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Thermal imaging of air infiltration around door frame
Lack of Air Barriers
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Thermal imaging of air infiltration at base and around electrical outlet
Lack of Air Barriers
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Thermal imaging of air infiltration at window and building corner
Lack of Air Barriers
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Air barriers have been voluntarily used and included as part of a prudent
design
however
That is about to change
Voluntary to Mandatory
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2012 International Energy Conservation Code will contain requirements for air barriers
Must pass one of three levels of performance:•Material•Assembly•Building
Rapidly Approaching Future
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Air permeance of less than or equal to 0.004 cfm/ft2 under a pressure differential of 0.3 in. w.g. when tested according to ASTM E 2178
Material Performance
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Average air leakage rate of less than or equal to 0.04 cfm/ft2 under a pressure differential of 0.3 in. w.g. when tested according to ASTM E 2357, E 1677, or E 283
Assembly Performance
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Air leakage rate does not exceed 0.40 cfm/ft2 under a pressure differential of 0.3 in. w.g. when tested according to ASTM E 779
Building Performance
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Air always flows from:
•High pressure low pressure
•Warmer colder
Causes of Air Movement
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Stack pressure occurs when atmospheric pressure differences exist between the top and bottom of a building
Winter Condition
Causes of Air Movement
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HVAC equipment can create pressure in the building
Causes of Air Movement
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Winds cause pressure differentials between the interior and exterior
Causes of Air Movement
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Exterior wall surfaces should shed water
Successful Building Enclosure
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Inevitably, some uncontrolled moisture-laden air will get past the primary
building cladding, then what?
Successful Building Enclosure
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There should be a barrier that does not allow liquid water to penetrate
Successful Building Enclosure
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Depending on the geographic location of the building, a barrier that controls the passage of water vapor may be required
Successful Building Enclosure
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There should be a barrier that prevents the passage of uncontrolled moisture-laden air from penetrating into the building
Successful Building Enclosure
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There should be a thermal barrier within the building enclosure that retards the movement of heat through the building enclosure
Successful Building Enclosure
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While water is essential to sustaining life, it is the primary enemy of the building enclosure
Successful Building Enclosure
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Liquid-applied•Exterior side of the wall•Different chemical formulas•Rolled on or sprayed on•Can be applied to almost any surface•Forms continuous,
seamless membrane
Types of Air Barriers
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Sheet-applied•Exterior side of the wall•Different sheet compositions•Mechanically attached•Seams are taped•Forms continuous membrane
Types of Air Barriers
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Sprayed foam•Interior side of the wall•Closed cell type•Seals joints, gaps, and small openings
Types of Air Barriers
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There are a considerable number of opportunities for joints, cracks, gaps, and openings
Cracks and Openings
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Examples of cracks and openings:
•Joints between differing materials
•Sealants with bond line failures
•Joints between rough openings and windows
Cracks and Openings
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Examples of cracks and openings:
•Cracks in masonry
•Joints between sheathing panels
•Joints around penetrations through the building enclosure
Cracks and Openings
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Must allow water vapor to pass through the material
Attributes of Air Barrier
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Must be continuous and free of holes
Attributes of Air Barrier
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Must be durable during construction
Attributes of Air Barrier
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Must be resistant to liquid water infiltration to prevent mold
Attributes of Air Barrier
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Must be resistant to air infiltration to eliminate those cold winter drafts
Attributes of Air Barrier
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Must be resistant to ultraviolet light degradation because it may be exposed for several months
Attributes of Air Barrier
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Must be durable over the service life of the building
Attributes of Air Barrier
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Liquid-applied air barriers must have the ability to bridge cracks in concrete masonry
Attributes of Air Barrier
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Generally the air barrier is located on the outside face of the sheathing or
concrete masonry
Location of Air Barriers
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Common Myth:“Vapor barrier on warm side in winter”
Myth Clarified:Generally applies to northern climates;vapor barriers usually not required in
southern climates
Air barriers should be used everywhere
Location of Air Barriers
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Every building, large or small, needs an AIR BARRIER
Final Word
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