Air Barriers (Building Envelope)
The Building Envelope is essentially the “skin” of a building. The quality of the Building Envelope will determine how well a building will function and its life span. The requirements of the Building Envelope will differ with the climate of the area. In areas where insulation is necessary the following requirements have been identified by Dr. Neil Hutcheon in the Canadian Building Digest – CBD48 (1963). Examination of building problems clearly indicates that the requirements of the Building Envelope most in need of solutions are air flow, water vapor flow, rain penetration, and durability. Building Envelope failures are evident as rain penetration, high energy costs, early deterioration of building components, and Sick Building Syndrome/Indoor Air Quality (IAQ) problems. Air leakage is the uncontrolled movement of air through the building envelope. This movement of air is caused by wind, stack effect, and fan pressures. The combined forces are significant and must be resisted by the air barrier system. Uncontrolled air leakage translates into: These issues have proven to be significant enough to effect building code changes. Air barrier technology is a rapidly growing concern for all designers and specifiers, and Henry® leads the industry with over 18 years of experience with successful, high profile projects. With over 17 completely integrated systems, our architectural services team can assist building owners, designers, and specifiers create an effective plane of air tightness throughout the building envelope. Theory On Air Barriers The history of air barriers can be traced to the early 70s during the energy crisis. Building professionals were looking for ways to make buildings more energy efficient and eventually realized this could be achieved by stopping uncontrolled air leakage through the building envelope. The term “air barrier” was quickly adopted. Air Barriers were first incorporated into the National Building Code of Canada in 1986. In the United States, requirements for air barriers can now be found in the Massachusetts Energy Code. Many other states and ASHRAE are currently planning to incorporate requirements for air barriers in their next code revisions. An air barrier must first and foremost resist air leakage. The loads involved are more significant than many designers realize. The Massachusetts Energy code, section 1304.1.2, states and air barrier shall “have an air permeability not to exceed 0.004 cfm/ft2 under a pressure differential of 0.3 in water.” Testing of air leakage is based on American Society for Testing of Materials (ASTM) E283, E330 and E2178. In these tests, a mock-up wall is constructed and covered with a membrane. The mock-up is then subjected to air pressures ranging from 1.6 lb/ft2 to 62 lb/ft2. The air leakage through the membrane is measured at all pressure levels and is inspected for visual delamination. All Henry air barriers have been tested by independent testing laboratories. Air Barrier membranes can be categorized in the following two types of air barrier: 1. Vapor Permeable Air Barriers: Henry vapor permeable air barrier membranes resist air leakage and rain penetration through the building envelope. However, since they are vapor permeable, they allow the diffusion of moisture, in the form of vapor. Therefore, they are not vapor barriers. In essence they can let the walls of your building “breathe.” Vapor permeable air barriers offer designers more flexibility in the positioning of the air barrier within the wall assembly. 2. Non-Permeable Air Barriers: Henry non-permeable air barrier membranes resist air leakage, rain penetration, and vapor diffusion. Therefore, they act simultaneously as an air barrier, a vapor barrier, and a rain barrier. Since these membranes also act as a vapor barrier, the positioning of non-permeable air barriers within the wall assembly is critical in avoiding potential condensation problems. Liquid Air/Waterproofiing Barriers Waterproofing systems are a combination of materials that act together to prevent water infiltration through the building envelope. No other manufacturer can offer you a more diverse selection of waterproofing products. • 790-11 Hot Rubberized Membrane “As much as 90% of all water intrusion problems occur within 1% of the total building or structure exterior surface.” Effective waterproofing starts with the proper selection of materials for your particular projects. Foam Air Barriers Air Barriers control the unintended movement of air into and out of a building enclosure. Air barrier systems are made up of a number of materials which are assembled together to provide a complete and total barrier to air leakage. The building enclosure includes all walls, roofs and floors of the building and can include connected parts or separations within a building. The air barrier system essentially “wraps” the building shell and ensures that it protects the building from air leakage and its adverse affects. These effects can range from energy, mold, occupant discomfort and more. They can also reduce the life span of a building. A properly functioning air barrier system provides a barrier against both the air leakage and the diffusion of air caused by weather, wind, stack and mechanical equipment pressures. Spray Foam Insulated Air Barrier Systems are fully-adhered, providing a seamless, monolithic air barrier that conforms to irregular shapes, slopes and allows easy detailing around penetrations such as pipes, windows, doors and sheathing fasteners. SPF air barriers contribute to improved building durability, energy efficiency, and to occupant comfort, health and safety. Not only does SPF provide the highest level of thermal insulation, it provides a monolithic, fully sealed air and moisture barrier. Its spray applied installation process speeds construction and reduces labor costs substantially. Alternate air barrier systems such as sheet goods require a great deal more labor for installation. Sheet goods do not possess the insulation (R-value) characteristics and are often susceptible to tears, and air leaks due to their reliance on proper seeming, adhesion and interface with the building’s façade. For the occupants to be comfortable, we condition the air in buildings. In summer or in cooling climates, we normally cool and dehumidify the air to a lower temperature and humidity that the exterior environment. In winter or heating climates, we normally heat and humidify the air to a higher temperature and humidity than the exterior. An air barrier assembly is a collection of air barrier materials and air barrier components assembled together in a specific manner. A wall air barrier assembly would include the main air barrier material and then use additional materials and components to join the air barrier materials together. The performance of a total air barrier assembly is far more important than the air permeance of the material itself. When conditioned air (heated, cooled or filtered) leaks out of a building, and unconditioned air leaks into a building, additional energy is consumed to re-condition the remaining air. Air leakage can result in increased energy consumption costs of up to 30%-40% in heating climates and 10-15% in cooling costs. Buildings which have a properly installed air barrier system can operate with smaller HVAC systems since they do not have to compensate for a leaky building. In many cases, the reduction in mechanical equipment size and cost can offset the cost of the air barrier system. Air barrier systems also provide a barrier to pollutants and other contaminants entering the building or the building enclosure. Water vapor, suspended particulates, dust, insects, odors/smells, are all contaminants we want to keep out of the building. Water vapors that leak into the building (from the inside in heating climates and from the outside in cooling climates) can condensate and forms liquid water a key ingredient to corrosion and the potential development of mold.
The Theory of Air Movement
1. Vapor Permeable or 2. Non-Permeable.
• Cold Applied Membranes
• Self-Adhered Membranes
• Thermofusible Membranes
• Prefabricated Drainage Composites
• Expansion Joints
• Waterstops
