“Combining the testing of the individual materials and accessories, as well as testing for the wall assembly is most effective. Testing on the material alone can provide misleading results,” writes Vanessa Salvia, a freelance writer who specializes in the construction industry. 7
Whole building tests, outlined in ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization, evaluate the assembly, its installation, and measure the building’s airtightness. The most common is the whole building blower door test, which is used to verify compliance with the airtightness goal. Additional details on orifice blower door testing are found in ASTM E1827, Standard Test Methods for Determining Airtightness of Buildings Using an Orifice Blower Door.8
How the whole-building blower test works
First, every opening in the building is sealed off. A membrane is placed at the blower door with a big fan at the bottom. The fan is turned on and air is sucked out of the house, creating a vacuum, during which gauges inside and outside the building measure air pressure. Changes in air pressure, air changes per hour (ACH), indicate the tightness of the building. The lower the number of ACH, the tighter the structure.
Quality control (QC)
The difficulty with air barriers is combining different building products to create a continuous air barrier around a building, making continuity the biggest challenge.
With building wrap, every different course of the wrap must be taped against the previous course in an airtight way. Additional steps and time invested in finding issues can increase costs. Using building wrap as an air barrier is increasingly becoming uneconomical due to the shortcomings associated with mechanical fastening and penetration; some now view building wrap as more of a WRB rather than an air barrier.
Self-adhered membranes take away the risks of penetrations because installers seal each additional course to itself. With self-adhered products, installation steps are priming, laying the material accurately, coming back with a hard roller to adhere membranes, and sealing it with termination mastic to maintain air continuity. However, each of these steps requires near perfect jobsite conditions since weather elements such as wind, dust, water, or frost can impede installation and quality.
When a self-adhered air barrier is not fully airtight, workers must go back and locate potential air leakage by peeling back layers or going inside and patching leaks. Self-adhered products, if not installed perfectly, can be more difficult to problem solve and more costly due to increased labor usage.
Fluid-applied membranes are simple to install but difficult to manage, in terms of finding a straight line, maintaining appropriate mil thickness, and allowing for differing curing environments. For example, wall application can be challenging, especially where requirements call for as much as 40 mils and as little as 15 to 20 mils. If sheathing is out of plane, or concrete blocks or poured concrete have pits and high spots, a leak is bound to occur. Application needs to be consistent at thick enough milage for airtightness and water resistance, but not thick enough to break budget with excessive material and labor costs.
Overapplying fluid-applied membranes can cause the product to run or droop. Installers must understand how products go on the wall, curing time, and proper sequencing. Quality control can involve looking for pits and voids, including pinholes and areas without continuity, since fluid-applied membranes shrink, move, and change form with building once cured.
Dry time and weather conditions are also key factors as both membrane barriers often need extended, dry, temperate conditions to ensure proper application and performance. As a result, newer liquid barriers have leveraged special chemistry, allowing consistent mils, quicker cure times, and the ability to be back rolled or not, depending on substrates. Their use in a school retrofit project illustrates some of the advantages.
Integrated WRB-AB sheathings innately contains most of the two barriers at the onset since they are adhered together. When installing the sheathing, most of the barriers are also installed. The only additional step is sealing penetrations, joints, seams, gaps, and rough openings to structural members by going over fastener heads with liquid flashing or tape. As a result, the only opportunity for an air leak is if there is a hole.
The integrated product itself has uniform thickness and can be visually inspected with relative ease, simplifying the guesswork related to many issues experienced with other technologies. Other benefits of an integrated WRB-AB system include not being weather dependent, requiring little to no cure time, and coming from a single source, which leads to increased support and supplier accountability. Integrated WRB-AB sheathing systems are easier to install and manage quality control, increasing the likelihood of successful airtightness and reducing rework and callbacks.
