Duct Sealing Tech Seals Project After Drywall

ohio state university aerosol sealant

Ohio State University finds aerosol sealant out of Berkeley Labs a project saver when a nearly completed building failed a pressure test. 

It had been nearly five years since construction first began on Ohio State University’s (OSU) new William Hall dormitory building. School administrators were working closely with contractors in preparation for the dormitory’s grand opening just weeks away. So it was with more than the usual amount of concern that project managers reacted to news that the building’s ventilation system failed to pass pressure tests needed to meet fire code regulations and targeted LEED requirements.


The state-of-the-art dormitory was designed with safety and energy efficiency in mind. With a goal of exceeding ASHRAE 90.1 energy ohoi state university air sealing standards by 30%, architectural considerations included naturally lit spaces, on-site renewable energy technologies, and a storm water sewage system, among other innovations. The building’s ventilation system consisted of 19 individual exhaust shafts, each made up of three layers of fire-rated drywall.


Still, the pressure tests revealed significant leaks in every shaft. So while the fire-rated dry wall was sufficient to keep out fire for up to three hours, with leaks, it did little to keep smoke from spreading from room to room.


The leaks would also have a significant impact on driving up energy usage. Results from initial tests showed that 30% to 45% of heating and cooling energy was being lost through the various leaks throughout the shafts. Additional energy would be needed to drive the exhaust fans at sufficient levels to ventilate all areas of the building.

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It was clear the leaks needed to be sealed. However, to do so, workers would have to access the entire length of each of the shafts, and that meant tearing down most, if not all, of the building’s newly constructed walls, manually locating and sealing each leak, and then rebuilding.


“This was no minor setback,” says Ruth Miller, senior project manager, OSU. “We were planning to open the doors to the new dormitory in just a matter of days, and now it looked like we would have to rip out a major portion of the work that had been completed and start over. This would put us way behind schedule and add hundreds of thousands of dollars to our construction costs.”


Then an engineer remembered hearing about a new duct sealing technology developed at Lawrence Berkeley National Laboratory that used an aerosol-based approach to sealing ductwork. Delivered as a mist of microscopic particles, the aerosol sealant travels along the inside of the ventilation shafts where it locates and seals leaks from inside out. After initial testing and proof of concept, the duct sealing team began work on tightening up all 19 shafts.


The process begins by blocking the wall registers so air can only escape through the leaks in the ductwork. The duct system is slightly pressurized to 0.1 in. WC, increasing to a maximum of 3 in. WC during the sealing process. The sealant is then heated up and blown into the ventilation shaft through an existing access point or through a temporary entranceway cut into the system. The dry, 7-10 micron-sized adhesive particles remain suspended in air as they travel throughout the ductwork until they reach a leak. Here they begin to accumulate around the leak, bonding to other sealant particles until the entire hole is permanently filled.


Unlike some sealants, such as those used for weatherization or material bonding, the aerosol sealant, or Aeroseal, is a vinyl acetate polymer with a rapid cure rate of approximately two hours. The sealant exhibits minimal VOC off gassing and its non-toxic properties afford it no OSHA maximum exposure limitations. The aerosol technology has been used to seal leaks in school buildings, health clinics, and hospital buildings among other facilities and, in many cases, has been used to successfully treat buildings while being occupied.


In less than two weeks, workers had each ventilation shaft sealed and operating to both fire code and stringent LEED Silver specifications. Aerosealing had located and sealed 98% of the leaks – without tearing down a single wall or disturbing any of the completed construction.


“Finding out about this new approach to duct sealing was a huge relief,” says Miller. “The innovation turned a nightmare situation into a relatively minor problem. It allowed us to stay on schedule and ensured that the new dormitory is the model of energy efficiency that it was designed to be.”


John Dixon is a freelance writer who has written a variety of published articles relevant to HVAC and related industries. He is headquartered in Portland, Ore.