Washing machine noise nuisance
Residents in a newly built state of the art care home raised complaints about noise nuisance due to the operation of washing machines located in a room above their bedrooms. These were industrial-sized washing machines that were operational almost constantly during the daytime until late in the evening to cater for the needs of the 250-bed care home.
Typically, utility rooms would be located on grade, that is either on the ground floor or the basement, rather than a thin suspended floor slab. However, since staircase free space is at a premium in care homes due to the fragility of its occupants, it is typical for care home designs to locate “back of house” activities on the upper floors.
A noise consultant was not appointed during the design stage and the two washing machines were built on top of a 100 mm thick concrete plinth (as a mitigation measure). For security reasons, the units were rigidly attached to the concrete base using two stabilisation screws. The general background sound level in the en-suite bedroom directly below the washing machines was an LAeq of around 25 dB. However, when one of the washing machines was operational, and when it reached the rinse cycle, noise levels in the room below were increased to an LAeq of 48 dB. During this measurement, it was subjectively noted that noise levels were dominated by the rattling of the door leading into the en-suite bathroom. Applying pressure onto the door made the rattling noise disappear, but noise levels were still above ambient levels. The movement of the ceiling light was also clearly evident during the measurement.
In order to increase the damping associated with the source of vibration, a wooden structure was built surrounding the washing machines, the restraining bolts on the washing machine were removed and a stabilisation balloon manufactured by Steady Spin Ltd (www.steadyspin.co.uk) was placed on top of one of the units and was inflated in order to provide movement stabilisation of the unit (this is a simple noise reduction solution to your home washing machine as well – give it a try). The noise measurement was repeated with this arrangement in place, and an LAeq level of 35 dB was measured in the room below, a substantial decrease of around 13 dB. The washing machine was then placed on various rubber mats, and these provided a further 3 dB of noise reduction.
Even though these measures reduced the noise impact of the washing machines substantially during the non-rinse/spin cycles, where the impact was now deemed acceptable, it was still considered to be a problem during the limited time spans when the machine’s drum was moving at high speeds, especially during the spin cycle.
As such, it was recommended that the solid suspended ceiling rods should be replaced with acoustic hangers utilising springs and neoprene bearings that provide at least 20 mm of deflection under load. Finch did not revisit the premises to retest the noise levels after the acoustic hangers were put in place since we were informed that the care home rooms below the utility room are now “quiet like a whisper”.
The same end client was in the process of designing a new care home nearby, and due to our success with the other scheme, we were appointed early this time around, to design a more fitting solution to the timber structure/balloon and rubber pads solution. In this development, the acoustic ceiling below the utility room was also put in, but the washing machines were placed on a carefully designed concrete inertia base. This base was “floated” on spring bearings that had a natural frequency under load sufficiently lower than the fundamental natural frequency of the suspended floor slab (and the forcing frequencies from the vibrating washing machine). A far more expensive solution, but clearly a lot more “elegant” as the architect said. Even if it was for a utility room.