Post on 15-Dec-2015
WALTER SCARBOROUGHCSI CCS CCCA SCIP AIAwscarborough@hbig.us214.491.7385
D+D Specifiers Series
Sponsored by
Air Barriers
• 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
• Vapor diffusion through materials was less than infiltration of moisture-laden air through openings in the building enclosure
Discovery of Air Barriers
• 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
“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
Air barriers can also function as a barrier to liquid water infiltration, while allowing water vapor diffusion
An Additional Function
Air barriers have been voluntarily used and included as part of a prudent
design
however
That is about to change
Voluntary to Mandatory
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
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
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
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
Stack pressure occurs when atmospheric pressure differences exist between the top and bottom of a building
Winter Condition
Causes of Air Movement
Inevitably, some uncontrolled moisture-laden air will get past the primary
building cladding, then what?
Successful Building Enclosure
There should be a barrier that does not allow liquid water to penetrate
Successful Building Enclosure
Depending on the geographic location of the building, a barrier that controls the passage of water vapor may be required
Successful Building Enclosure
There should be a barrier that prevents the passage of uncontrolled moisture-laden air from penetrating into the building
Successful Building Enclosure
There should be a thermal barrier within the building enclosure that retards the movement of heat through the building enclosure
Successful Building Enclosure
While water is essential to sustaining life, it is the primary enemy of the building enclosure
Successful Building Enclosure
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
Sheet-applied•Exterior side of the wall•Different sheet compositions•Mechanically attached•Seams are taped•Forms continuous membrane
Types of Air Barriers
Sprayed foam•Interior side of the wall•Closed cell type•Seals joints, gaps, and small openings
Types of Air Barriers
There are a considerable number of opportunities for joints, cracks, gaps, and openings
Cracks and Openings
Examples of cracks and openings:
•Joints between differing materials
•Sealants with bond line failures
•Joints between rough openings and windows
Cracks and Openings
Examples of cracks and openings:
•Cracks in masonry
•Joints between sheathing panels
•Joints around penetrations through the building enclosure
Cracks and Openings
Must be resistant to air infiltration to eliminate those cold winter drafts
Attributes of Air Barrier
Must be resistant to ultraviolet light degradation because it may be exposed for several months
Attributes of Air Barrier
Liquid-applied air barriers must have the ability to bridge cracks in concrete masonry
Attributes of Air Barrier
Generally the air barrier is located on the outside face of the sheathing or
concrete masonry
Location of Air Barriers
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