Acoustic Analysis of Proposed Buildings

A

TERM PAPER

ON

ACOUSTIC ANALYSIS OF PROPOSED BUILDINGS

BY

ADEKUNLE KEHINDE JAMES

ARC/09/7343

AND

ADEBISI TOYOSI RAPHAEL

ARC/09/7341

SUBMITTED TO

THE DEPARTMENT OF ARCHITECTURE,

SCHOOL OF ENVIRONMENTAL TECHNOLOGY,

FEDERAL UNIVERSITY OF TECHNOLOGY,

AKURE, ONDO STATE.

COURSE TITLE- BUILDING SERVICES III

COURSE CODE- ARC 507

LECTURER-IN-CHARGE

PROFESSOR O. O. OGUNSOTE

JULY 2014.

TABLE OF CONTENT

1.0Introduction

2.0Acoustic analysis of proposed buildings

2.1Workspace and office designs

2.2Classrooms

2.3Multifamily housing designs

2.4Library designs

2.5Common area designs

3.0Application of acoustic analysis

3.1HVAC noise issues

3.3HVAC acoustical strategies

3.4Natural ventilation

3.5Sound masking

4.0Conclusion

References

1

1.0INTRODUCTION

Acoustics of buildings is that part of the science of physics which deals with the control of sound in buildings. Room acousticsorbuilding acoustics is the science and engineering of achieving a good sound within a building and is a branch ofacoustical engineering. Architectural acoustics can be about achieving good speech intelligibility in a theatre, restaurant or railway station, enhancing the quality of music in a concert hall or recording studio, or suppressing noise to make offices and homes more productive and pleasant places to work and live in. Since the purpose of this control is to create conditions by which people can hear with comfort, it is necessary to consider not only the principles of sound but to take into account also the phenomena of hearing.This science analyses noise transmission from building exterior envelope to interior and vice versa. The main noise paths areroofs,eaves,walls,windows,doorand penetrations. Sufficient control ensures space functionality and is often required based on building use and local municipal codes.

2.0ACOUSTIC ANALYSIS OF PROPOSED BUILDINGS

During the design process, the architect is expected to put into consideration the acoustic functionality of the spaces created in his design. Good acoustic planning would lead to better designed and comfortable interior spaces. People live in the interior of buildings hence spaces where people are expected to spend more time should be positioned in areas with less noise. Possible noise paths can be controlled with the use of insulation and good acoustic materials.

2.1WORKSPACE AND OFFICE DESIGNS

The acoustical environment of a workspace is typically given little or no attention during project planning and design. The functionality and aesthetics of the workspace are usually the primary focus of the designer. Too often overlooked, are the factors contributing to the productivity of employees occupying the work space. Providing a comfortable environment for employees contributes significantly to their optimum performance and reduced absenteeism. Workspace comfort is really a combination of factors that includes daylighting and electric lighting, indoor environmental quality, temperature, and acoustics. The assault on ears in the workplace can come from traffic noise outside, mechanical equipment in adjacent spaces, and copiers, phones, and voices within the workspace.

Besides the design team's focusing on the project's functionality and aesthetics, building acoustics is so often given low priority because it competes for limited project dollars with a number of other project goals, including: sustainable design/development, physical security/anti-terrorism, information technology/telecommunications, and building automation and controls. Though there are some differences in the acoustical requirements of offices, classrooms, and conference rooms, several common noise problems affect these occupancies:

• Too much noise outside the building entering the space
• Too much noise from adjacent spaces, and
• Lack of sound control in the space itself.

Noise in these occupancies is typically not at a high enough level to be harmful to human hearing. Rather, the noise is distracting from concentration on work or study and provides less than ideal working and learning environments.

SITE SELECTION

A satisfactory indoor acoustical environment actually starts by knowing what is going on outdoors. Follow these guidelines when selecting a site for an office building or educational facility:

• Avoid sites in high noise areas such as airfields, highways, factories, and railways.
• Ensure compatibility with existing facilities. It is a fatal error to site a school in an industrial area, for example.

Determine what else is planned for the site in the future. Your building may be the first one built, but if future buildings are acoustically incompatible with yours, significant remediation measures may be necessary to return the interior sound environment to an acceptable level.

What do you do when the site is predetermined by the client?

When the site is predetermined and is too noisy for an office building or educational facility:

• Incorporate appropriate sound control measures
• Avoid through-the-wall, package terminal air conditioners (PTAC)
• Zoning- position quiet spaces away from outside noise sources.

To protect the spaces in a building from noise from a nearby highway or railway, lay out the building so that restrooms, mechanical and electrical equipment rooms, and other less noise-sensitive spaces are adjacent to the roadway. When designing a campus near high noise activity, locate gymnasiums and other less noise-sensitive facilities closer to the noise source and place buildings needing quiet surroundings in the shadow of those facilities.

As always, while siting for noise control, incorporate sustainable site planning into the decision-making process. For example, an earth berm with low-growth, drought-tolerant plants can act as a noise barrier from highway traffic, can meet sustainable development principles, and can help meet security requirements for standoff distance from buildings. This system is also known as screening.

GLAZING

Windows and glazing are key elements of the building envelope. These elements must allow daylight to enter the space, reject heat and glare, control sound and, for some projects, be blast resistant. The extent of windows and glazing, and their size and location are decisions that must be made in the project concept phase to ensure proper windows and glazing are chosen. Keep in mind that multiple glazing types are likely for many projects based on the building orientation, proximity of intrusive noise sources, and vulnerability assessments and risk analysis.

OPEN OFFICE ENVIRONMENTS

Open office environments provide greater flexibility than enclosed offices by using easy to relocate low-height, moveable partitions or systems furniture to form individual workspaces, rather than employing full-height permanent partitions. The initial cost for open office environments is less than that for enclosed offices and reconfiguration can be done rapidly at minimal cost. These factors have led to an increased use of open office environments in both the federal and private sectors. Acoustical problems have surfaced in open office environments causing employees distraction, stress, and interference with telephone conversation and normal work routine. How serious is the problem of poor workplace acoustics? The Centre for the Built Environment (CBE) at U.C., Berkeley conducted post-occupancy Evaluation (POE) of 15 buildings by 4,096 respondents in a variety of office configurations. Over 60 percent of occupants in cubicles think acoustics interfere with their ability to get their job done.

2.2CLASSROOMS

Classrooms are environments designated for learning, not just for school-age children, but for adult training as well. Classrooms have become multimedia communications environments, further increasing the importance of classroom acoustics. Good acoustics for learning support easy verbal communication, which requires low noise levels and very little reverberation. In the past, classrooms may have been constructed without adequate consideration of sound acoustical principles. Sources of noise hampering students' concentration include: outside of the school (vehicular traffic and aircraft flyover) the hallways (foot traffic and conversation) other classrooms (amplified sound systems and inadequate partition sound transmission loss) mechanical equipment (compressors, boilers, and ventilation systems), and inside the classroom itself (reverberation).

To reduce noise from adjoining classrooms, do not have doors adjacent to each other or have doors directly across from each other. Rather, offset the door locations to extend the sound travel path from one classroom to the next. This strategy works well with conference rooms and private offices as well.

2.3MULTIFAMILY HOUSING DESIGNS

There are several issues that must be addressed concerning acoustics in a multi-family project. These issues stem from the two types of sound that must be controlled: airborne sound and impact sound. A typical airborne sound is music or talking. A typical impact sound is the footfall sound of an upstairs neighbour.

Many builders seek to increase the marketability of a development by promoting "luxury" acoustic conditions. While potential residents will certainly appreciate the effort, you can expect construction costs to increase as a result. There must be a balance between the acoustics and the budget while, at the same time, the expectations of the residents should be met. It should be noted, however, that even when the acoustical issues in multi-family housing are addressed, some noise transfer between units is inevitable. Describing the units as "sound proof" or making statements such as, "you'll never hear your neighbours" creates unreasonable expectations and should be avoided.

Factors that contribute to noise transmitting into a neighbouring unit include residents' living habits, background noise and the isolation quality of the partitions. Obviously, the amount of transmitted noise will be highly dependent on the amount of noise created in the adjacent spaces. Additionally, if a room has a relatively high background noise level, this will help to mask the transmitted noise. However, if a room has a relatively quiet background noise level, the transmitted noise will be more noticeable.

The following points should be considered in mass housing or multifamily building designs.

• All air-gaps and penetrations must be carefully controlled and sealed. Even a small air-gap can degrade the isolation integrity of an assembly.
• The perimeter of the wall and any penetration must be sealed air-tight with a non-hardening acoustic sealant.
• Avoid the installation of back-to-back penetrations (outlets, light switches, and phone jacks). Consider installing a putty pad to the back of all outlets in party walls.
• Ideally, elevator shaft footings, floor pads, masonry shaft walls, elevator equipment mountings, etc. should be totally isolated from the building structure. Structure borne noise/vibration from elevator operation may be extremely annoying. Additionally, any penetration or air gap in or around the wall must be sealed airtight with a non-hardening acoustic sealant.
• The building code specifies that the entrance doors from interior corridors shall have an STC rating of 26 or higher. Obviously, the higher the STC rating of the doors, the better the isolation. However, if the seal around and under the door is not maintained, selecting a high rated door is meaningless. Ideally, drop seals that seal to a threshold (not carpet) can be installed. An acoustically absorptive ceiling and carpet in the corridor will help to control the noise levels within the corridor.
• The majority of noise concerns can be alleviated through proper space planning. Sensitive areas should not be located near potentially noisy areas. Potentially annoying sound transmission from floor to floor (for example, from a restroom or kitchen above a bedroom) can be mitigated through the vertical mirror of spaces. Horizontally, potentially noisy areas (such as elevators, vending rooms and laundry facilities) should not be adjacent to bedrooms.
• Although the building code does not address plumbing noise, this issue can be a major source of noise complaints. Plumbing noise can be both airborne and structure borne. To reduce plumbing noise, pipes should be resiliently mounted, that is, adequately insulated from their supports. To further reduce plumbing noise, the pipes should be wrapped with pipe lagging material.
• Any roof-mounted equipment should be analysed for potential noise/vibration impact.
• Be concerned about exterior noise impacting the interior rooms (such as a nearby airport or freeway). The majority of this noise is transmitted through the windows. Upgrading the window assemblies might be necessary.

2.4LIBRARY DESIGNS

For proposed library design, the following points should be considered

• Recommended reverberation time is 0.8 to 1 second.
• Absorptive materials are needed to reduce the reverberation time.
• If domes or other concave surfaces are desired, they must be treated with absorptive materials to reduce unwanted reflections.
• Beware of potential noise impact to your space from exterior sources and/or excessive HVAC noise. To help protect your design, the NC level should not exceed 30 to 40. When specifying NC, specify an actual rating, such as NC 35, rather than a range, such as NC 30-35. Although specifying a lower number will ensure minimal background noise, it might be cost prohibitive to achieve. Be realistic about the amount of acceptable noise and the project's budget when specifying an NC level. NC is not a consideration for an outdoor space.
• The majority of noise concerns can be alleviated through proper space planning. If possible, place noisy equipment and activities in remote areas.

2.5COMMON AREA DESIGNS

The main goal of good acoustics analysis in a common area is to absorb excessive noise from employees conversing, televisions, snack machines, etc… while ensuring noise within this space does not distract employees working nearby.Many noise control issues can be alleviated through proper space planning. Avoid placing potentially noisy spaces, such as break rooms, close to critical areas. Also consider using an absorptive ceiling system in this type of space to help control reflections and the building up of noise.

3.0APPLICATION OF ACOUSTIC ANALYSIS

3.1Daylighted Offices and Classrooms

When open ceilings are designed into a building project to optimize daylighting into offices and classrooms, quite often suspended acoustical ceilings are eliminated and the exposed surfaces are painted with highly reflective paint to throw daylight well into the space. The sound absorption value lost by the absence of the suspended ceiling must be replaced in other ways to prevent the space from becoming a highly reverberant field. High reverberation times are not conducive to concentration and effective learning.For office areas with exposed ceiling structure, specify low reverberation times (0.6-0.8 seconds) to minimize echoing and unwanted sound reinforcement.In other words, the majority of the effective sound absorbing materials in a space are in the suspended acoustical ceiling. If you design the space without a suspended acoustical ceiling, you must provide sound absorption somewhere else: partitions, banners, drapes, etc. Carpet on the floor does not replace the lost overhead sound absorption though it reduces footfall noise.

3.1HVAC Noise Issues

HVAC systems should be specified to have an ambient sound level compatible with the occupancy. If HVAC system is too noisy, conversation may be difficult. If HVAC is too quiet, unwanted conversations and other distracting noises will be heard. Productivity is affected. Follow recommended background noise reduction design criteria for typical occupancies in Architectural Graphic Standards. For example, in office buildings:

Small conference rooms NC 30-35

Small private offices, libraries NC 30-35

General offices NC 35-40

Computer rooms NC 40-50

3.3HVAC acoustical strategies

Avoid through-the-wall air return louvers that draw air from one room through another in private offices, conference rooms, and other rooms where confidential discussions are expected to occur. All air returns should be ducted.

Do not locate air supply or return registers close to each other on opposite sides of a partition wall. Doing so will cause sound to pass directly from one room to another, negating the acoustical value of the partition.

3.4Natural Ventilation

Natural ventilation using operable windows is desirable in appropriate climate zones. Before committing to that strategy, be aware of the outdoor acoustical environment around the building. Unacceptable levels of continuous or intermittent noise outside can preclude the use of this sustainable design strategy.

3.5Sound Masking

Sound masking introduces unobtrusive background sounds into the office environment to reduce interference from distracting office sounds and render speech from co-workers virtually unintelligible. Sound masking works by producing sound electronically, similar to that of softly blowing air, which is projected through speakers installed above the tiles in the ceiling. This sound is evenly distributed throughout the area being masked and can be adjusted to the individual privacy requirements in any given area. In an open plan office without a suspended ceiling, speakers could be set on the systems furniture or even under the raised floor. Sound masking should be used in open and closed office designs when ambient sound level is too low. It increases productivity, improve worker morale, and enhance speech privacy.

4.0CONCLUSION

Acoustic is one of the factors that most affects the deterioration of environmental qualities i.e. factors that are likely to cause discomfort in buildings. Acoustical analysis takes into account the study of sound in a room including its transmission, intelligibility of voices and the level of ambient sound inside a building.