Sound Transmission Indoors — Integrated Windows

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Many airport authorities have implemented a sound insulation program for residences located within the Community Noise Equivalent Level contour of 65 dBA. The effectiveness of this approach is ensured by sealing building envelopes. Increased sound insulation generally improves thermal insulation and lowers energy demand. However, this traditional method of noise mitigation has a side effect: it degrades indoor air quality (IAQ), because most of these buildings obtain their fresh air through infiltration. With reduced infiltration, contaminant concentration and humidity increases. High humidity leads to a higher risk of condensation that, in turn, can lead to other IAQ problems such mold and bacteria growth. Although IAQ problems may be mitigated by using a mechanical ventilation system, such an action increases construction costs and subsequent energy use.

The purpose of Project 26 was to investigate windows' environmental performance because the windows in a residential building are often considered the weakest link in the sound insulation program. Our current efforts represent a step to achieve an optimal solution for providing sound insulation while the improving the IAQ and energy efficiency for residential buildings near airports.

The research

There were two themes in Project 26. Theme I was a study of various issues affecting noise ingression through windows in residential buildings. Theme II focused on the energy performance and the associated effects on IAQ due to window sound insulation.

Theme I aim was to develop numerical models for evaluating the transmission of low frequency noise (LFN) through elastic panels such as windows, doors, walls, and roofs. The numerical models and simulations were optimized for applicability to residential buildings in airport neighborhoods. 

The second theme was dedicated to investigate the possible use of ventilated windows for sound insulation in buildings. In particular, the capability of energy conservation and improvement of the indoor air quality for the use of this type of windows was examined. A numerical model based on the EnergyPlus program ( a whole building energy simulation program that engineers, architects, and researchers use to model energy and water use in buildings) was developed to calculate the building energy demands during the cooling and heating seasons in seven U.S. climate zones in the U.S. The IAQ was assessed by a multizone airflow network model known as CONTAM.


Theme I – Noise intrusion

  • A series of parametric studies was conducted to investigate the effect, on sound transmission through a single-pane window, caused by fluid loadings, window frame elastic support, the window aspect ratio , and the effect of damping. The transmission of a broad band LFN was explored
  • A method is proposed to reduce the transmission of LFN through windows
  • A numerical model has been developed to assess transmission through double- and triple-pane window.

Theme II –Assessment of energy efficiency and IAQ of different types of windows
Numerical analyses were conducted to simulate energy efficiency and IAQ for different types of windows installed in typical apartments and detached houses located in different climate zones in the U.S.:

  • The modified Energy Plus program was used to simulate the energy efficiency in typical buildings. The numerical study indicated that the dual-airflow windows can achieve greater energy savings in the heating season than in the cooling season.
  • CONTAM was used to simulate IAQ in typical buildings. The numerical results indicated that  use of exhaust fans in bathrooms and kitchens could not maintain an acceptable IAQ level throughout the day. However, both supply-airflow windows and dual-airflow windows could be used for ventilation to maintain good IAQ.

For more detail on these outcomes, please read our final report, downloadable below.

Next steps

Three tasks are recommended for the next phase of study:

  • Develop integrated models/tools to analyze a few typical residential buildings, with and without energy-efficient windows, near airports, in different climate regions. The integrated model should identify the combined problems of acoustics, IAQ, and energy efficiency in residential buildings in proximity to the airport.
  • Conduct full-scale field experiments to examine the environmental performance of different types of windows including energy-efficient types (e.g., dual-airflow windows). Measurements of acoustic performance, IAQ, and energy efficiency should be conducted during two-week periods in the summer and winter at one or more geographical locations.
  • Examine the current best practices of IAQ and energy efficiency of residential buildings in conjunction with the guidelines for sound insulation for FAA-funded noise insulation projects. Conduct cost-benefit analysis of various methods (e.g., change from mechanical to natural ventilation in buildings) for improving IAQ and energy efficiency in building structures while maintaining specified noise level reduction.

Participating university

Purdue University

Lead investigator

Kai Ming Li, Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University,

Project manager

Bill He,


  • Assessment of Windows on Noise Intrusion, Energy Efficiency, and Indoor Air Quality for Residential Buildings near Airports. Kai Ming Li, J Stuart Bolton, Qingyan Chen. Project 26 final report. June 2012. Report No. PARTNER-COE-2012-004. Download (pdf 6MB)