For some time, the U.S. Department of Energy has attributed 40 percent of annual HVAC energy use in typical construction to air leakage. A newly released report by the National Institute of Standards and Technology (NIST), titled “Investigation of the Impact of Commercial Building Envelope Air Tightness on HVAC Energy Use,” confirms this hypothesis. To view this report, click here.
In the NIST report, different types of commercial buildings throughout the United States were studied, and a considerable amount of air-leakage and energy-consumption data was compiled. Using conventional ASHRAE calculations for energy consumption in HVAC operations, differences in energy usage were determined as a result of reduction in building air leakage. The reduced air-leakage numbers in this report correspond to easily attainable building air tightness where an air barrier is used. The results are quite compelling, especially for heating-dominated climates.
Target Levels with an Air Barrier
In the heating-dominated climates, the payback period for using an air barrier is less than 5 years. Further tightening of the building enclosure, which is attainable with a high-quality air barrier installation, pushes the annual energy savings in heating-dominated climates to over 40 percent!
How Does This Study Relate to Carlisle’s Air Barrier Technology?
Carlisle Coatings & Waterproofing (CCW) Inc.’s membrane air barriers, CCW-705 self-adhering and Barriseal fluid-applied, provide airtight wall construction, meeting or exceeding the air-leakage target indicated in this study. Also, the CCW membrane air barriers are completely water- and vapor-proof. Moisture management - a huge issue - was not addressed in the NIST report.
What is an “Air Barrier”?
An air barrier is a material or an interconnected assembly of materials that retard the passage of air. An air barrier may or may not be vapor permeable. According to the Massachusetts energy code, an air-barrier material must retard the passage of air similar to ½-inch-thick drywall or better. Many materials qualify as air barriers. In practice, the tricky part of properly installing a complete air barrier on or within the building envelope is continuity and durability. If the air-barrier materials are not continuous, or their junctions are not durable for the life of the building, then the building has no air barrier. CCW membrane air barriers meet the requirement of providing a true air barrier assembly over the building envelope, as they are fully adhered and airtight over the walls, including penetrations and joints. CCW membrane air barriers also maintain continuity over all six sides of the building by tying into the roof and foundation with durable, flexible, and airtight overlaps.
Is House Wrap an Air Barrier?
In the conventional-application manner, house wrap is a water-resistive barrier (WRB), not an air barrier. The NIST report mentions house wrap as an air-barrier option. Certain house wraps can be installed as air barriers. In order to provide a true air barrier, the house wrap must be fastened and anchored in a very deliberate manner with all joints completely taped and all openings, transitions, and terminations flashed and tied into the house wrap. Even when applied properly, house wrap does not provide the same security in an air barrier application as a fully-adhered CCW membrane air barrier. Tears or perforation from subsequent construction steps can completely compromise the performance of a house wrap air-barrier system. Also, the many taped joints and details of a house wrap air barrier do not have the same long-term durability as a fully adhered CCW membrane air barrier. Unlike house wrap, the CCW membrane air barriers are self-sealing around fasteners. Furthermore, since they are fully adhered, even significant flaws or damage to the CCW membrane air barrier have little effect on the overall performance.
Can’t You Just Tape the Joints Between Sheathing or Insulation Board to Make an Air Barrier?
The NIST report mentions taping of sheathing joints as an air-barrier option. Since the sheathing itself is an air barrier, taping the joints makes a continuous wall air barrier. However, unlike CCW’s full coverage membranes, tape has many exposed edges where water can get in and work the bond loose over time. Also, workmanship in taping the joints is critical, as any wrinkle or fishmouth would present a breach in the system. Then, there is still a requirement to tie the wall air barrier to the roof and foundation. CCW Window & Door Flashing over primed surface makes an effective air barrier sheathing tape. However, the CCW full wall system membrane air barriers are the best way to go.
Won’t an Air Barrier Keep the Building from “Breathing”, Causing Mold and Sick-Building Syndrome?
A building’s occupants do indeed require fresh air for health and well-being. The best way to provide fresh air to the occupants is the use of the ventilation system, which is already defined by ASHRAE code. Some buildings also have operable windows, which can be opened during fair weather. A building should not “breathe” through uncontrolled air leakage. Uncontrolled leakage of air across the building envelope often causes a number of serious problems, including:
- Occupant discomfort from drafts and cold/hot spots.
- Unwanted transfer of odors or contaminants from one part of the building to another.
- Prevention of effective function of the HVAC system.
- Increase in energy costs.
- Condensation within the building envelope, which can cause damage to the building components and mold.
So, the building “breathing” by means of air leakage generally does more harm than good. A properly installed air barrier makes a more comfortable, efficient, and long-lasting building.
