Air Barriers:¬† An Evolution
The building envelope has become the focal point of architects, engineers and consultants during the very recent past. The wall assembly is now viewed with the same scrutiny that roofing systems have experienced for many years. In order to make a building energy efficient and to control moisture infiltration, air/vapor barriers are commonplace on almost all commercial structures today. Increasing awareness of the importance of the building envelope has occurred due to reports such as the United States Department of Energy’s conclusion that up to 40 percent of energy needed to heat and cool a building is lost from air leakage. State building codes typically reference or adopt ASHRAE Standard 90.1 – Energy Standard for Buildings Except Low-Rise Residential Buildings.
As with any other product or business, the air/vapor barrier business continues to evolve from its earliest forms of black tar paper found behind stucco systems, and siding in older residential homes. Roofing felt paper was used in residential and commercial construction for a number of years with varying degrees of success. The next step in the evolution was the use of building wraps that were more durable than roofing felts. Today’s building wrap systems include detailing tapes for laps plus window and door openings to create an airtight barrier.
As the industry continues to mature, commercial construction has seen a dramatic growth in the use of fluid-applied barriers along with self-adhesive detail tapes. These types of barriers have distinct advantages over previous materials, with the ability to provide total continuity of the barrier, as we know even the smallest of gaps can significantly affect performance. The newer fluid-applied materials provide a “structural” building envelope barrier with continuous contact to the substrate capable of resisting forces from wind, mechanical pressurization and stack effect. One of the challenges associated with fluid-applied products is the ability to control application thickness, but with more contractors becoming experienced installing the fluid-applied systems, that concern seems to be diminishing somewhat. Manufacturer jobsite inspections are becoming increasingly important to verify proper installation methods.
The debate continues within our industry: “breathable or non-breathable.” Many believe that all wall systems should be able to breathe and allow vapor transmission through the wall assembly, while others still believe Northern climate wall systems with outboard rigid insulation should incorporate a complete air and vapor barrier system. The breathable air barrier actually does not have a specific location within the wall assembly, and, in many cases, ease of an effective installation may determine its location. In most cases, no matter the type of barrier system used, the normal placement is on the outer face of CMU or exterior sheathing, which provides the optimum location to create a totally complete and continuous barrier.
One of the biggest issues confronting designers and installers today is the compatibility of numerous components with the masonry wall. Air barriers, thru-wall flashings, wire reinforcement and anchoring systems must work in conjunction with one another. Fluid-applied and peel-and-stick barriers, unlike previous weather barrier materials, provide self-sealing characteristics that are extremely important with anchoring products that are normally penetrating at 16 inches on center throughout the wall. With many types of flashing materials on the marketplace such as stainless-steel, copper laminates, flexible membranes must be determined as to their compatibility with the barrier material and detail tapes being used. Another compatibility concern involves silicone and polyurethane sealants with all of the above mentioned materials at locations such as door/window openings, where the sealant can become the transition from the barrier membrane to the frame of the opening. As more compatibility issues are discussed, the ability for the specifier to be sure that all components will function together becomes increasingly important. Manufacturers must have various materials tested together as a complete system to ensure a complete functioning wall assembly. Our industry has already made great strides in this area with the development of a new testing procedure, ASTM E-2357, which expands upon the basic material testing of the past and now tests the assembly of the barrier, anchoring system and flashings. This is a tremendous step forward; however, since few manufacturers offer all three parts of assembly, it will become incumbent upon various manufacturers to work together with products to meet this new criteria. For too many years, the architect was tasked with pulling together all of the materials without much coordinated help from those manufacturers to create a wall system that will meet today’s high-performance wall types.
Another type of barrier system showing up in the marketplace today is the spray foam insulation within the cavity area, which can provide a continuous layer of insulation and a barrier system as well. There are two different types of spray foam materials, with one being a closed-cell formulation that acts as an air and vapor barrier when installed, and the other an open-cell material that gives you a breathable air barrier layer. The biggest issue with the spray foam system is the ability for the applicator, normally trained and licensed by the manufacturer, to maintain a controlled thickness of product. The number of qualified applicators at this time is small, due the lack of a major presence of this type of system being used. This system seems to be much more popular in northern climates of the United States and in Canada at this point.
Although barriers have become an integral part of today’s masonry wall systems, careful consideration still must be taken in selecting anchoring systems that will perform well with the barrier material. The systems must also perform the No. 1 goal of properly holding the veneer in place. The growth of selecting an anchoring system based strictly on the recommendation of a barrier manufacturer, with little to no knowledge of the criteria for effectively holding a veneer in place, can be a dangerous situation for all parties involved. This is exactly why material manufacturers must work together to provide the most complete information possible for the designer and contractor. Just as important is the roll of the applicator for the proper installation of the system.
As the air barrier industry continues to grow and mature, newer issues become more prevalent, and all parties involved from the architect to the product manufacturer to the installer must have an understanding of each of their roles in developing effective continuous barrier systems. Detailing is extremely important, especially the details where the barrier ties into a roofing system and also the below-grade waterproofing. Failure to tie these systems together will result in an ineffective building envelope that does not perform its intended purpose. To be sure, growth will continue and with that will come more questions and issues that everyone must together solve.
- 57High-performance buildings are constructed to maximize energy efficiency, durability and overall occupant comfort. As the demand for these buildings continues to increase, it is important to understand that one of the key aspects of achieving this is proper building enclosure design and overall wall system performance.