Session Info

Unintrusive Building Air Leakage Visualization and Measurement Using Background Oriented Schlieren Photography


Building leakage accounts for about 4 quadrillion British thermal units of energy consumption in the US and can contribute to poor indoor air quality, occupant comfort, and building material durability. Locating and sealing leakage sites is critical to saving energy and to improving indoor building conditions and durability. State-of-the-art methods involve intrusive blower-door testing and infrared imaging, which require extensive expertise to correctly identify and interpret air leakage sites.

Air leakage visualization

Background oriented schlieren (BOS) photography detects shifts in background texture to visualize transparent fluid flow in a sequence of images. It requires very small pressure differences between the building and outdoors, so it does not require a blower door and is therefore less intrusive to building occupants, making the technique more adoptable in the market. Since air is visualized directly, there is no risk of incorrectly identifying areas of leakage. Furthermore, BOS can measure the flow rate of individual leakage sites so that leaks can be prioritized during sealing efforts.   


This approach to locating and measuring air leakage in buildings is quicker and less intrusive than current approaches, which is critical to enabling the energy retrofits of millions of existing buildings in the U.S. New laws will require better than state-of-the-art methods to finding air leakage in buildings. These include New York City Local Law 97, which requires most buildings greater than 25,000 square feet to meet stringent energy efficiency and greenhouse gas emission limits by 2030. The added capability of measuring the flow of individual leaks means that sealing leakage can be prioritized, sealing the biggest leaks first, which ensure buildings meet energy efficiency requirements with reduced time and effort.


Boudreaux, P., Venkatakrishnan, S., Iffa, E., and Hun, D. 2022. “Application of reference-free natural background oriented schlieren photography for visualizing leakage sites in building walls.” Building and Environment 223, 109529.

Boudreaux, P., Iffa, E., Venkatakrishnan, S., and Hun, D. “What does it take to see air leakage through a building envelope?” ASHRAE 2022 Buildings XV Conference. December 5, 2022. Clearwater Beach, FL.

Intellectual Property

“Building leakage detector using reference-free background oriented schlieren photography,” Invention Ref. No. 202205206


For more information, please contact Andreana Leskovjan (865-341-0433,



Philip Boudreaux

Philip Boudreaux