Care must be taken to locate noise-producing mechanical equipment—such as heat pumps, air conditioners, and generators—so the noise produced during its operation is not excessive for neighboring properties. The city has maximum sound levels which must be met at each property line. These apply to equipment located on the roof, on the ground, outside the building, at an exterior wall, and inside a building where noise may be transmitted to an exterior wall through a duct and/or louver. Most noise problems occur between mid-evening and sunrise when ambient sound levels in the neighborhood are low due to less outdoor activity and traffic.
The City of Bellevue
The noise ordinance is located in Bellevue City Code Title 9.18, Noise Control. It restricts the noise level at the property line in residential zoning districts to 45 dBA at night (10 p.m. to 7 a.m.) and 55 dBA during the day.
Land Use Code Section 20.20.525 requires an owner to build a new single-family home or add more than 1,000 square feet to an existing home to locate mechanical equipment in the rear yard, placed no less than five feet from any property line.
Other mechanical equipment (not a new home, not adding more than 1,000 square feet to an existing home) placed in the side yard outside of the minimum side-structure setback must include sound screening to reduce noise impacts.
City of Seattle
Seattle Municipal Code 25.08.410 regarding exterior sound level limits, states A. The exterior sound level limits are based on the Leq during the measurement interval using a minimum measurement interval of one minute for a constant sound source, or a one‐hour measurement for a non‐continuous sound source. For sound sources located within the City, the exterior sound level limits are as follows:
District of Sound Source
Residential Commercial Industrial
District of Receiving Property
Residential (dB(A)) (Leq)
55 57 60
Commercial (dB(A)) (Leq)
57 60 65
Industrial (dB(A)) (Leq)
60 65 70
Seattle Municipal Code 25.08.420 regarding night-time noise limits, states A. Between the hours of 10 p.m. and 7 a.m. during weekdays, and between the hours of 10 p.m. and 9 a.m. on weekends and legal holidays, the exterior sound level limits established by Section 25.08.410 are reduced by 10 dB(A) where the receiving property lies within a residential district of the City.
The nighttime noise level of 45 dBA is similar to bird calls. Manufacturer specifications for mechanical equipment typically include decibel ratings. For example, heat pumps and air conditioners are tested to a standard that gives them a manufacturer’s sound power rating usually in the 70–80 dBA range. This would require the mechanical equipment to be placed from 40 to 100 feet from the property line to meet maximum nighttime noise levels.
Contact us for a noise survey meeting City Code.
