17 October 2012 — US academic John Goins is one of the authors of a research paper that looks at the issue of noise in buildings with operable windows. Sure, these can provide better thermal comfort, he says, but what about the noise from traffic or congestion when the windows are open?
Professor Goins, who will be Sydney on 13 November to deliver his views of thermal comfort at the Property Institute of Australia/Property Funds Association conference, Profitable Sustainability, looked at 23,000 office building occupants’ perspectives on the issue. Fellow authors of the original paper User perspectives on outdoor noise in buildings with operable windows, are Chungyoon Chun, PhD, Yonsei University, Hui Zhang PhD University of California, Berkeley.
Following is an edited version of the paper.
Office workers generally prefer access to a window. Studies suggest that the sunlight windows provide is relaxing and the presence of a window is thought to increase motivation. Windows that are operable provide additional benefits to occupants such as an improved ability to manage their comfort. In fact, occupants can be comfortable over a wide range of temperatures in some buildings with operable windows. Since occupants can be comfortable during more conditions in such a building, the heating, ventilation and airconditioning system demand is reduced, which also saves energy. Unfortunately, most office buildings include sealed – rather than operable – windows in the name of tightly controlled indoor environments. Therefore, most occupants miss these additional benefits and building owners miss potential energy savings.
While there are many positives to operable windows, there are potential negatives too. Dust, pollen and other pollutants may enter the building via outside air. Operable windows may present safety concerns by offering additional entry points into the building. Additionally, occupants in buildings with operable windows will likely be exposed to more outdoor noise than occupants in a sealed buildings will. These aspects may hinder the inclusion of operable windows in new buildings and retrofit installations in existing buildings.
This paper analyses occupant perceptions of outdoor noise in an attempt to addresses concerns about outdoor noise intrusion. More specifically, it presents analysis of six variables related to outdoor noise. It compares noise responses in operable and sealed buildings between differing land use densities, for example suburban or downtown; from occupants near and far from windows; by how far above ground-level noise the occupant sat; whether the building had double-paned glass in its windows; and over several window to wall ratio groupings. The study’s sample is 92 office buildings in four countries, representing approximately 23,000 occupants.
The effect of noise on office occupants is certainly worth considering.Poor acoustic environments can interfere with communication, create annoyance, stress and impede work performance. The World Health Organization recommends a background noise level lower than 45 decibel(A) for good speech intelligibility – the ability to understand others. The American Society of Heating, Refrigerating and Air-Conditioning Engineers also suggests a noise level less than 45 dB(A) for open plan offices.
Noise from outdoor sources would add 15dB(A) to any existing interior noise so that interior noise levels in operable buildings would need to be lower than in sealed buildings to meet these levels. It is not known how many office buildings in operation meet these standards. Better monitoring and reporting is needed according to the National Institute of Building Sciences. The literature makes clear however, that acoustics in general, falls short of office workers’ expectations.
Workers in open office environments report the worst acoustic problems and this pattern persists even in “green” rated buildings. Occupant comments express frustration and distress about poor acoustic environments, which may affect morale. Finally, absenteeism may also increase if acoustic conditions are bad enough.
The relationship between noise and the performance of office workers is especially well researched. One study showed that noise under 85dB – the level of a commercial truck – slowed work performance, but did not affect accuracy. Noise of this sort would also hinder telephone and other conversations. More recent work has expanded on these findings by showing that reading tasks are most affected by noise, a common task among office workers. The frequency of noise matters as well, with unpredictable noise also being problematic for occupants. Construction noise and sirens might fall into this category.
Noise is clearly a problem for occupants. This paper’s concern is the degree outdoor noise is perceived to be a contributor to noise problems in offices. More specifically, noise from traffic, construction and other outdoor activities and equipment. It is well established that traffic noise is a particular source of noise annoyance.
Data and Methods
The Centre for the Built Environment has developed a web-based survey about indoor environmental quality. The survey asks about seven indoor environmental quality areas including noise and acoustics. When respondents indicate dissatisfaction with noise, they are asked follow-up questions about the sources of their dissatisfaction. The list of sources includes both interior and exterior noise concerns. Respondents can write in additional sources of dissatisfaction if needed. Occupants are also offered the opportunity to write free-text comments about noise.
The survey has been continually administered in buildings since 2000. The complete dataset now includes responses from over 575 buildings and over 65,000 people. The set of buildings is a convenience sample. Still, the database is statistically very powerful due to its size. The survey instrument is largely the same in each building, so responses can be compared across buildings. Questions include:
You have said you are dissatisfied with the acoustics in your workspace. Which of the following contribute to this problem? (Check all that apply)
- People talking on the phone
- People talking in neighbouring areas
- People overhearing my private conversations
- Office equipment noise
- Office lighting noise
- Telephones ringing
- Mechanical (heating, cooling and ventilation systems) noise
- Excessive echoing of voices or other sounds
- Outdoor traffic noise
- Other outdoor noise
For each building, CBE also captures over 100 building characteristics, including indicators of land use density, window to wall ratio, number of storeys, whether the windows have double-pane glass and whether the windows open. The data used in this paper represent the buildings for which all of the aforementioned factors are completed. This resulted in a sample of 92 buildings and approximately 23,000 occupants.
Numeric data for each respondent were analysed, as were the 2100 free text comments about noise. Numeric data were analysed in Excel. All numeric results are statistically significant to a 99 per cent confidence level unless otherwise noted. Text data were analysed in SPSS Text Analytics for Surveys. Over 80 per cent of the comments were categorized and included in our results.
About two-thirds of the sample buildings are in the US. The remaining buildings are in Finland, Canada and Australia. A majority of the buildings are situated in central business districts – downtowns – densely populated areas likely to have high levels of outdoor noise. Eighty per cent of the buildings were sealed, while 20 per cent offered operable windows. For both sealed and operable buildings, a majority of occupants site more than 15 feet from their nearest windows.
The data show that occupants in buildings with operable windows are more satisfied than their counterparts in sealed buildings. More specifically, occupants near windows in operable buildings are more satisfied than their counterparts near windows in sealed buildings. This pattern continues to be true even in potentially noisier areas like downtowns and other urban areas. When asked about specific sources of dissatisfaction, interior noise sources were much more of a problem than outdoor ones like traffic noise. This may explain why noise satisfaction does not respond much to operable windows, as indoor noise is a much greater concern for occupants.
People talking was the greatest concern. While 80 per cent of those dissatisfied and near windows in operable window buildings cited people talking as a problem, only 20 per cent cited traffic noise as a problem. People talking is cited nine to eleven times more frequently that outdoor noise sources.
People that complain about phones ringing are likely to be among the occupants most dissatisfied with noise. People talking follows this. Traffic noise and other outdoor noise sources are towards the bottom of the list, suggesting that these are not extreme annoyances when they are a problem. The respondents are like to be only slightly dissatisfied whereas the aforementioned would be very dissatisfied.
Among outdoor noise sources of concern, the free text comments highlight that construction noise can be a significant problem when present. It is the second most mentioned outdoor noise source with 37 occurrences among over 1000 free-text comments about noise sources. It is however, very temporal and generally recedes with time. By far most text comments relate to physical features of the office or the design of individual workspaces.
While there is only small dissatisfaction with outdoor noise, it is still worth considering what design elements might help attenuate dissatisfaction. There may be locations where outdoor noise is of special concern. For this reason, we consider traffic noise (the more problematic of the two outdoor sources) and the effect of insulated (double-pane) glass, window to wall ratio, and the floor on which the occupant sits, for occupants near windows for all buildings. We consider both operable and sealed buildings together here since it is likely that an occupant would close an operable window when outdoor noise is a problem. Thus, the sealed and operable building would have the same condition in this circumstance.
There is a small increase among those near windows that cite traffic (and other outdoor noise sources) as problems in buildings without insulated glass. This suggests that double-pane glass (or greater) may help attenuate dissatisfaction with outdoor noise to a small degree.
There are also small differences in traffic noise dissatisfaction between floors. The data show a constant decrease in traffic noise as a source of dissatisfaction as the floor number increases. This pattern holds for floors 1 through 9. Traffic noise dissatisfaction increases at floor 10 however.
Buildings with a facade composed of one-quarter to one-half windows show the most traffic dissatisfaction. Strangely, buildings with more windows have less traffic noise issues reported. This suggests that there is no relationship between window-to-wall ratio; some other building characteristic, a confounding variable, might be at play here.
While noise more generally is a problem for occupants in many buildings, these data suggest outdoor is not a significant problem for office occupants as survey respondents near windows are more satisfied with noise than people without windows. Occupants near operable windows are the most satisfied overall. Among occupants dissatisfied with noise, indoor noise sources – like people talking – are about 10 times more prevalent in offices. Among problematic noise sources, a phone ringing is most likely to create the strongest negative response.
Construction noise is of concern to occupants when present. The number of reports of problems with construction noise is small, but the comments are very passionate. For this reason, this noise source deserves special attention.
When outdoor noise is a problem, several options exist to attenuate dissatisfaction. Traffic noise complaints recede in the presence of double-pane windows and when occupants are on higher floors. This suggests that one way to respond to outdoor noise complaints is to move noise sensitive occupants to a higher floor or put them near windows with two or more panes of glass.
The authors would like to thank the anonymous reviewers of this paper for their insights and Charles Salter for his advice on this work.
This paper first appeared in the University of California’s escholarship website