Masonry Magazine July 2009 Page. 33
Air Barriers and Building Enclosures
According to the Air Barrier Association of America, the air permeance of any air barrier material is 0.02L(sm2) at 75Pa. While many materials singularly can achieve this air permeance, the air barrier materials must be tied together in a continuous plane to form an assembly, with a maximum air leakage of 0.2 L(sm2) at 75 Pa. Finally, the actual air barrier system consists of these air barrier assemblies in a continuous plane of air tightness for the entire building enclosure, with a maximum air leakage of the whole building at 2.0 L(sm2) at 75 Pa.
While air barriers can be vapor permeable or vapor impermeable, there are several requirements of the air barrier system that must be met. An air barrier system must be able to resist live loads (e.g., wind pressure, HVAC mechanical loads, etc.) without failing, and the system must completely wrap the entire building envelope completely, without presenting any entry points for air leakage. Each air barrier component, assembly and the connections between them must be connected, from the roofing system to the below-grade structure, to resist these loads. A failure of any part of the system is a failure of the system as a whole.
While the 2006 IBC does not require an air barrier in exterior wall systems, experts suggest that we should expect a mandatory air barrier requirement with the 2009 IBC. Several factors play a part in this expectation.
Air Barrier Requirements and Standards
First, the well received National Building Code of Canada requirements specify the acceptable level of air permeability of 0.02 L/(s-m2) at 75 Pa pressure (0.004 cfm/ft2 at 1.57 psf); several states and municipalities in the United States have adopted this requirement as well.
Second and more importantly-AHRAE 90.1 "Energy Standard for Buildings Except Low-Rise Residential Buildings" was updated in 2006 requiring the use of air barriers, which is adopted by reference by the IECC, which once again will be adopted by reference by the IBC in 2009.
Types of Air Barriers
THERE ARE SEVERAL DIFFERENT TYPES of air barrier materials available:
* Mechanically-attached membranes, also commonly referred to as housewraps, that allow vapor transmission
* Self-adhered membranes, aka peel and stick, which are typically waterproof and vapor impermeable
* Fluid-applied membranes, such as heavy-bodied paints or coatings
* Closed-cell spray-applied polyurethane foam, which typically provides insulation as well
* Thermofusible materials, typically made with SBS-modified asphalt that is "melted" to the substrate.
AIR-TIGHTTM LIQUID MEMBRANE
* A latex asphalt emulsion air and vapor barrier used as a waterproof coating for a variety of applications and variety surfaces such as metal, wood, concrete and all exterior sheeting.
* ICC approved for below grade use
* 100% Asbestos Free
* VOC Free
* Available in Permeale & Non-Permable Formulations
* Dries in 15 minutes, cured in 24 hours
* Easily applied by brush, squeegee, or spray equipment, yielding a coverage of 25 sf per gallon
AIR-TIGHTTM SELF-ADHESIVE MEMBRANE
Sandell's Air-Tight™ Self-Adhesive Membrane is a fully adhered, self-adhering, Air & Vapor Barrier membrane for use with concrete, masonry, gypsum or wood wall construction. Usage shall comply with typical wall flashing details.
Sizes:
* 75-foot rolls - 8" and 36" widths
AIR-TIGHTTM TAPE
Sandell's Air-Tight™ Tape is a resistant weather barrier that protects a structure from air, vapor, wind, and rain. It resists the elements with unfailing performance and prohibits the harsh environment from entering a structure. It is applied around door and window penetrations.
Sizes:
* 30 or 40 mils thickness and in lengths of 75'
* Custom slitin 3", 4", and 6" widths
Available in:
* 5 gallon pails
* 55 gallon drums
* 270 gallon totes
310 Wayto Road
Schenectady, NY 12303
Toll Free: 1-800-283-3888
Phone: 1-518-357-9757
829-34th Street
Birmingham, AL 35222
Toll Free 1-877-Sandell
Phone: 205 263-1030
7373 S. 6th Street
Oak Creek, WI 53154
Toll Free 1-800-323-3565
Phone: 414-764-0058