Noise complaints are a prevalent and challenging problem for facility managers. While the most common are related to a loud residential or commercial neighbour, the source of annoying sounds may be environmental (air, rail or road traffic), generated by building-related equipment (HVAC, plumbing or electrical systems), or occupant-induced or controlled (speech, physical activity, entertainment systems).
Pump up the Volume
Two factors affect the sound (or annoyance) level of noise: the sound power produced at the noise source; and the distance and path the noise takes to the point of complaint. Sound and vibration energy can travel long distances, in all directions, and through air, water, wood, concrete and metal. Airborne sound, travelling as air pressure waves, can enter a living space or workplace through small hidden gaps and openings found around piping, ductwork and electrical junctures. Structure-borne sound, on the other hand, can travel through solid building materials, such as ceilings, floors and walls. This can be problematic (and particularly disruptive) when a commercial business, such as a fitness or childcare centre, restaurant or bar, is situated above, below or beside a typically quiet space like a spa or corporate boardroom.
A Healthy Dose of Sound
Complaints about noise do not necessarily mean there is a building deficiency. Some audible noise from building systems or adjacent units is normal for a typical commercial property and does not warrant the implementation of noise control measures. So, before embarking on a potentially complicated (and expensive) investigation into the noise nuisance, it may be worthwhile to consult an acoustical engineer who can determine whether the noise is unreasonable for the building type and whether it is due to excessive sound transmission.
In multi-residential buildings, airborne sound transmission limits are set by the building code. The limits are expressed as sound transmission class (STC) ratings. The higher the rating, the better the sound isolation. The Ontario Building Code, for example, requires a STC rating of 50 as a minimum acceptable value for wall construction and STC 55 in specific areas. The National Building Code of Canada requires an apparent sound transmission class (ASTC) rating of 47, which accounts for flanking paths, instead of STC 50.
Frequently, an acoustical assessment will find that the walls or floor assemblies meet building code standards. These requirements are sometimes lower than occupants’ expectations of quiet enjoyment of their property, resulting in disbelief that they do not support their contention and frustration.
Code compliant wall and floor assemblies often provide sound insulation that is good for high frequencies, reasonable for mid-frequencies and generally fair to poor for lower frequencies. This means voices, which are higher frequency, are typically not heard or are unintelligible, while the deep, low frequency rumbles of an entertainment system’s subwoofers can penetrate structural barriers and be heard despite the wall or floor being to code. Even for high and mid-frequencies, code compliance does not guarantee inaudibility, which also depends on the sound levels on the source and the background sound levels on the receiver side.
Clamouring For Quiet
Unfortunately, there are no criteria set out in the building code regarding sound levels and sound transmission in commercial spaces. It is often up to the discretion of the developer, building owner or facility manager to determine whether a nuisance noise should be remedied, unless limits and restrictions have been set out in a lease agreement. These may be expressed as STC and/or IIC (impact isolation class) ratings, or overall sound levels in decibels (DBA).
Potential noise intrusion issues can be anticipated before, and noise mitigation recommendations incorporated into, a lease agreement to ensure noise and vibration does not, under practical circumstances, intrude into other spaces.
In the case of a fitness club looking to rent space in a commercial building, for example, an acoustical engineer can create scenarios in order to assess the potential for sound and vibration intrusion from physical activities into adjacent tenanted areas. These scenarios may involve using a PA system in the space to recreate the rhythm, amplitude and frequency content characteristics of a typical cardio workout class, including the music played during the exercise routines.
Similar conditions can be created in areas to be used for aerobics, treadmills and weights. Analysis may indicate the need for suitable floor slab stiffeners and isolated flooring to mitigate perceptible vibration or structure-borne noise in adjacent tenanted spaces.
Since the potential for audible structure-borne noise from fitness activities can be difficult to predict, the acoustical engineer may also recommend including best practices for laying floor systems in the lease agreement. Basically, an appropriate resilient underlayment should be installed below the subfloor (usually wood, though concrete is sometimes required) before the surface floor covering (typically a sports rubber flooring) is laid. This technique is effective in controlling or damping sounds in a fitness facility located in a building with ‘sensitive’ occupant neighbours.
To ensure timely investigation by an acoustical consultant and a potentially more economical assessment and mitigation solution (if mandated), it is recommended that facility managers keep a noise log that tracks the time, frequency and characteristics of noise occurrences. While the complainant should input this information, facility management is ultimately responsible for maintaining the log. It should be regularly reviewed and used as a tool to investigate whether there may be any corresponding occurrences far removed from, or seemingly unrelated to, the occupant’s unit. This may lead to the origin or cause of the noise issue in question.
For instance, mechanical equipment (HVAC systems, pumps, motors and chillers, backup generators, elevators, and garbage compactors, among others) can generate enough vibration that, if not properly vibration-isolated, may radiate throughout the building as structure-borne noise. Occupants may perceive this as a neighbouring noise problem, however, the source is actually far removed in a remote part of the building and the sound only occurs at certain times related to that piece of equipment.
Jessica Tinianov is a senior acoustical engineer at HGC Engineering. The acoustical consulting group specializes in the analysis and design of noise and vibration controls for building services, and architectural design for residential, commercial and institutional spaces, including acoustic optimization, sound intelligibility and privacy solutions