Sealing air leaks in any building can make it more comfortable and efficient. But owners of existing buildings often resist spending the time and money to address the problem. In fact, addressing air leaks in existing buildings is like the Rodney Dangerfield of Rodney Dangerfields. In the words of the late comedian, "they just don’t get no respect."
Even without air leaks, existing buildings don’t get no respect unless they are historic or otherwise noteworthy.
And when there are air leaks, most owners don’t pay attention until the signs are impossible to ignore: ice dams building up, mold growth, or people near the windows are shivering. At that point an expert might be recruited to scope out the problem and recommend a solution.
Drivers for Air Sealing
Leaky buildings are often ignored in the face of other problems that are perceived as more critical, reports Jenny Carney of WSP in Chicago. “In larger commercial buildings, even if they know that they have an air leakage problem, it’s rare that fixing it rises to the level of capital investment,” Carney says. “When it does,” she continues, “it’s driven by occupant comfort or other issues.”
To make things worse, “most people don't even realize that they have a leaky building unless they are getting drafts or have freezing pipes, cluster flies, or icicles coming out of the curtainwall,” reports building forensics expert Terry Brennan of Camroden Associates.
In Canada, many architects are aware of the general importance of airtightness in building enclosures thanks to the network of provincial Building Enclosure Councils. Seeking to establish similar councils in the U.S., architect and building enclosure consultant Wagdy Anis of Anis BE Consulting, LLC connected the American Institute of Architects with the National Institute of Building Science to jointly convene the groups. This model began in Boston, according to Anis, and “there are now thirty around the country.”
These councils are mostly focused on designing new buildings, according to Anis, who helped establish the groups. “Consultants get called in for forensic work due to problems in [existing] buildings,” he says. “Architects don’t typically get called in for that.”
Owners don’t often seek out air-sealing improvements to save energy. “We would love to convince our clients of the long-term value of our approach based on energy benefits alone, but often the driver is some other problem,” says Catherine Muller, president of Air Barrier Solutions, a company dedicated to air sealing and insulating existing buildings.
Air Barrier Solutions is typically called in due one of these common performance problems:
Ice dams: warm air leaking into roof cavities melts snow on the roof. The water runs down and freezes at the eaves, where it builds up, resulting in puddles behind it and potentially dangerous icicles along the edge.
Thermal comfort complaints: leaking air makes it hard to keep people near the perimeter comfortable, either because they’re getting drafts directly from outdoors or because the whole perimeter zone suffers from cooling and heating systems that can’t keep up with the load.
Humidity control problems: air that leaks in isn’t conditioned for appropriate indoor humidity levels.
Window condensation: cold air leaking in near windows lowers their surface temperature to the dew point of indoor air.
Mold or mildew: condensation on cool surfaces inside the building or within building cavities supports microbial and fungal growth, which can release allergens or toxins, and damage building materials.
Noise from outside sources: sound travels via pressure waves in the air, so leaking air means more noise transmission.
Odors: smells from outdoors bypass a building’s filtration systems when they leak in through the walls. In multifamily buildings, compartmentalizing individual units to prevent odor from spreading is a common challenge.
Buildings with tight performance requirements, such as an historic building with old finishes or a museum housing humidity-sensitive art, are especially at risk. “It might be deteriorating plaster now that a historic building is air conditioned or controlling temperature and humidity for museum exhibits—it is amazing how many problems trace back to a defective air barrier,” notes Muller.
Buildings can also fail—at least in the commercial sense—by not keeping up appearances. In certain markets, owners will invest in reskinning a building to update its look and to keep it competitive with newer peers.
Lorne Ricketts, a building science engineer with RDH Building Science in Vancouver, British Columbia, has studied the drivers for building envelope upgrades. The Belmont is a high rise apartment building he investigated that had enclosure elements wearing out, and was starting to look old and dated. “The building is in a high-end neighborhood and the owners wanted something that reflected a more modern design while also providing needed renewal,” he explains about the building's owners.
Once the owners started looking into upgrading the look of the building, they saw the opportunity to improve it in other ways. Now that the project is completed, the owners are pleased with the energy savings, but even happier with how comfortable and quiet the apartments are.
Saving energy is usually a fringe benefit to a building envelope upgrade that is driven by other factors, but sometimes an audit points to air sealing specifically as a worthwhile energy conservation measure. “For existing buildings, infiltration is often the biggest envelope energy driver,” reports Andrea Love, building science cirector at Payette in Boston. “Unfortunately,” she continues, “very little data exists on large scale commercial buildings infiltration, and it is difficult and expensive to test whole buildings so it very rarely happens.”
Energy audits are one common way that leaky buildings are identified if their other symptoms haven’t already raised air leaks as an issue. Jenny Carney is also founder of the BIT Building program, which aims to encourage and support managers of existing buildings—including underperforming buildings where resources are limited—to improve energy, water, and waste footprints. In BIT, as in LEED, the required energy audit will show strategies that will lead to performance improvement, according to Carney. “The assessment would determine if envelope measures are part of the solution,” she explains.
Even audits tend to undervalue envelope improvements, however, because they’re often done by people whose expertise—and sometimes incentives—are tied to mechanical systems. “If software like Air Barrier Solutions’ CHIEFPlus were available to more people doing audits, they might identify air leakage as an opportunity more often,” says Carney.
How big is the energy opportunity?
According to the latest Commercial Buildings Energy Consumption Survey (CBECS), in 2012, the U.S. had more than 5.5 million commercial buildings. These buildings collectively use nearly 7 quads of energy—that’s quadrillion—or 7 x 1015 Btu. Pushing for net-zero energy in new buildings is great, but without addressing this huge energy load in existing buildings we won’t make much of a dent in near-term carbon dioxide emissions.
Only 670,000 of those 5.5 million buildings are over 25,000 ft2 in floor area, but those larger buildings are responsible for nearly 70% of the energy use. The larger buildings also contain most of the floor area, but that doesn’t explain all of their energy appetite: their average energy use intensity (EUI) is just over 84 kBtu/ft2, compared to 80 for all commercial buildings.
Almost 36% of this energy is used for heating and cooling, for a total of 1.7 quads. Adding in the energy lost during conversion and transmission, that number is 2.8 quads, or about 3% of total U.S. energy consumption.
The handful of studies that have measured air leakage in large buildings find that they vary widely, from quite tight to very leaky. When they were built and where they are located doesn’t seem to matter much, but tall buildings do tend to be much tighter than short ones.
A study that modeled the air sealing opportunity in U.S. Army barracks found that tightening them up from 1 CFM75/ft2SA (cubic feet per minute of air leakage at pascals of pressure per square foot of building shell area) to 0.25 would save between 6% and 52% of total energy use. In a military office building those numbers are lower, ranging from less than 1% in a mild climate to 14% in a very cold climate. A 2005 U.S. Department of Energy-funded study of commercial buildings predicted energy cost savings ranging from 3% to 36% by sealing up buildings from typical levels to a high standard of tightness. The low ends of these ranges, in hot humid climates, don't account for the full energy load of dehumidifying outside air—so the actual savings are higher.