Typical exterior noise sources
For the purposes of building codes and ordinances, exterior noise sources are sometimes classified as mobile noise sources, stationary noise sources, or construction noise.
Planes
Aircraft noise is generally perceived as a discrete event, and although it is not always a problem for occupants, the sound of flyovers and take-offs are often audible inside buildings. The Federal Aviation Administration (FAA) produces contour maps of flyover noise expressed in terms of Ldn levels, for use in planning and assessing the impact of aircraft noise. It is important to have access to these maps when designing sound-sensitive buildings near an airport or flight path.
Trains
Train noise is treated similarly to aircraft noise, although train pass-by events are generally of longer duration than aircraft flyovers. Location of rail lines, especially for freight, must be taken into consideration when planning construction of sound sensitive buildings. The Federal Transit Administration (FTA) uses one-hour Leq or Ldn as the principal noise descriptors for mass transit noise, depending on the adjacent land use. Both are useful for planning and assessing new building design near railways.
Automobiles
The noise signature for vehicular traffic is characterized by fluctuating levels, punctuated with periodic noise ‘spikes,’ caused by trucks and buses. Design guidelines published by the Federal Highway Administration (FHWA) allow the use of one hour Leq or L10 in the analysis of traffic noise assessment.
Construction
Construction noise sources comprise both mobile (e.g. vehicles) and stationary (e.g. compressors, piledrivers, and power tools) sources. Noise levels generated by long-term construction projects must be considered when assessing the environmental noise level of a new building site.
Mechanical
Mechanical equipment associated with industrial operations and building ventilating systems are the primary external stationary noise source that designers must take into consideration. This equipment includes condensing units, chillers, transformers, emergency generators, cooling towers, exhaust fans, and rooftop air-handling units (AHUs). As sound pressure levels may approach 100 dBA within 3 m (10 ft) of some equipment, it is vitally important to be aware of the location of such equipment when designing for new sound-sensitive buildings nearby.
Other
Other stationary sources worth noting include crowd noise related to playgrounds or spectator events and noise from amplification systems. Although people are not usually considered stationary noise sources, sound generated at outdoor gatherings may cause considerable annoyance to adjacent communities. For example, the sound pressure level generated by spectators at outdoor sporting events may exceed 90 dBA.
Code requirements regarding noise
There are various forms of noise ordinances. Some define absolute sound pressure level thresholds
of acceptability, while others provide a maximum incremental limit, or threshold of change above existing background noise levels at neighboring locations. Some noise ordinances are even source-specific.
For example, according to the Philadelphia Department of Public Health’s Noise and Excessive Vibration Regulations, amplified sounds from restaurants and bars cannot exceed 3 dBA above the ambient sound level at the neighboring property line. Similarly, sound from commercial air-conditioning systems cannot exceed ambient levels by more than 5 dBA. Elsewhere, fixed daytime and nighttime sound level limits may be established, tabulated with daytime and nighttime maximum levels similar to what is shown in Figure 1. It is also not unusual to encounter a requirement for the maximum permissible increase above ambient at the property line to be limited to 10 dBA during daytime hours, and 5 dBA at night.
An understanding of the applicable local noise ordinance sets an expectation for normal maximum environmental noise levels in an area that is otherwise not burdened by loud mobile or stationary noise sources. The new building envelope can then be designed with these limits in mind.
