Chapter 4 — Acoustics, Sound Insulation and Noise Control

Acoustics, Sound Insulation

and Noise Control

4.1        purpose

 The purpose of this chapter of the Code is to provide acoustical, sound insulation and noise control requirements in buildings.

4.2        Scope

 In this chapter, each of the different occupancies is covered basically in two parts. The first part identifies different areas and aspects of outdoor and indoor noise sources. The second part specifies the planning and design recommendations covering the spatial, architectural and technical aspects of noise reduction measures within or outside the building.

4.3 TERMINOLOGY

 This section provides an alphabetical list of the terms used in and applicable to this chapter of the Code. In case of any conflict or contradiction between a definition given in this section and that in Part 1 or any other section, the meaning specified in this section shall govern for interpretation of the provisions of this section.

        BEL :  See Sound Intensity Level.

        CYCLE : See FREQUENCY.

 dBA :  Result of a sound pressure level measurement when the signal has been weighted with a frequency response of the A curve. The dBA curve approximates the human ear and is therefore used most in noise control regulations. The relationship of various internationally standardized weighting curves for sound levels is given in Appendix D.

        DECIBEL (dB) :  See Sound Intensity Level.

 DIRECT AND REVERBERANT SOUND : When a noise source is operating in a room, the noise level at any position may be regarded as consisting of, first the direct  sound, that  is the sound travelling directly from the source to the position under consideration, and second the reverberant sound, that is the sound reaching the position after multiple reflections from the room surfaces. As a working rate, the direct sound  is considered to predominate for a metre or so from the source.

ECHO : Echoes are long delayed discrete sound reflections of sufficient intensity to be clearly heard above the general reverberation in a room.

FLUTTER ECHO :  A quick succession of echoes; it may be present in small rooms as a disturbing phenomenon.

 FREQUENCY : The frequency of sound is the number of vibrations per second of the molecules of air, generated by the vibrating body. One complete movement to and fro of the vibrating body  is referred to as a 'cycle'. Frequency is expressed as the number of cycles per second (cps); it is also referred to  as Hertz (Hz).

 INTENSITY : Intensity at a point is the average rate at which sound energy is transmitted through a unit area  around the point and perpendicular to the direction of propagation of sound.

        L10  :  L10 is the average of all hourly values of sound level (in dB) of traffic noise which is exceeded 10 per cent in a given period of time.

 LOUDNESS : Loudness is the sensation produced in the human ear and depends on the intensity and frequency of sound.

 NOISE : Noise is defined as unwanted sound. Noise condition vary from time to time and a noise which  may not be objectionable during the day may be increased in annoying proportions in the silence of the night, when quiet conditions  are essential.

 NOISE EXPOSURE FORECAST (NEF) : Noise exposure forecast at any location is the summation of the noise levels in perceived noise level (PNdB) from all aircraft types, on all runways, suitably weighted for the number of operations during day time and night time.

        NOISE REDUCTION (NR): Noise reduction (NR) is a general term for specifying sound insulation between rooms.  It is more general than SOUND TRANSMISSION LOSS (TL). If all boundary surfaces in the receiving room are completely absorbent, the NR will exceed the TL by about 5 dB, i.e.  NR  =  TL + 5dB.

 PERCEIVED NOISE LEVEL : Perceived noise level expressed in decibels (abbreviated PNdB) is a quantity developed to evaluate aircraft noise to account for greater human sensitivity to high frequency sound. PNdB calculated from measured noise levels are more high frequency weighted than dBA and correlate very well with an average listener's response to aircraft noises of widely varying character.

 REVERBERATION : The prolongation of sound, as a result of successive reflections in an enclosed space, when the source of the sound has stopped is called reverberation.

        Reverberation Time (RT) :  The reverberation time of a room is defined as the time required for the sound pressure level in a room to decrease 60 dB after the sound is stopped, and is calculated by the formula  RT  =  

 where,

        RT        =        reverberation time

        V        =        room volume, m3

        A        =        total room absorption, m2

        x        =        air absorption coefficient

 Recommended optimum reverberation time of various uses of Assembly buildings are indicated in Appendix E.

 SOUND TRANSMISSION CLASS (STC) : To avoid the misleading nature of an average transmission loss (TL) value and to provide a reliable single figure rating for comparing partitions, a different procedure for single figure  rating, called sound  transmission class (STC) rating, of a partition is determined, by comparing the 16 frequency TL curve with  a standard reference  contour, the sound transmission class contour. STC ratings of some common walls and floors are given in Appendix F.

 SOUND TRANSMISSION CLASS CONTOUR : The sound transmission class contour is a standard reference contour with which the 16 frequency TL curve is compared to determine the sound transmission class of a partition.

 SOUND TRANSMISSION LOSS (TL) : The sound transmission loss, or simply transmission loss (TL), of a partition, is a measure of its sound insulation. It is equal to the number of decibels by which sound energy is reduced in passing through the structure.

 SOUND INTENSITY LEVEL : Sound Intensity Level is measured in terms of the unit Bel, which is defined as the logarithm of the ratio of the sound intensity to the minimum sound intensity audible to the average human ear. The unit DECIBEL (db) is one-tenth of a bel. Thus,

        Sound Intensity Level = log  bels   =  10 log  decibels

        where,         I         =        Sound intensity in watt cm2, and

                Io          =        Sound intensity audible to the average human ear taken as 10-16 watt/cm2.

 SONIC BOOM : Noise phenomenon due to the shock waves projected outwards and backwards through the atmosphere from leading and trailing edges of an aircraft travelling at supersonic speed. The waves are discontinuities of atmospheric pressure and are heard as a characteristic double report which may be of sufficient intensity to cause damage to buildings, etc.

 WAVELENGTH : The wavelength of sound is the distance between the centres of compression of the sound waves. It is dependent upon the frequency of the sound.

4.4GENERAL NOISE LEVELS : OUTDOOR

4.4.1        Adequacy  in Planning and Design

Planning and design of buildings shall take into consideration all sources of noise mentioned in             Sec 4.4.2 and keep provisions for control thereof within buildings.

4.4.2        Sources and Levels of Outdoor Noise

 The following sources of outdoor noise shall be taken into consideration for planning and design of buildings:

a) Traffic noise

(Road, rail, aircraft etc.)

Considerations for air traffic noise levels are given in Appendix G.

b) Noise from built-up areas

(Industries, commercial buildings, offices, public buildings etc.)

 For acoustic design of buildings, a noise survey shall be undertaken. (See Appendix H for frequency values and noise levels of some common sources of noise).

4.4.3        Planning and Design Considerations

 The following requirements shall be fulfilled in the planning and design process :

a) The planning shall be undertaken in such a manner that the noise can be kept at a distance. A drop of 5 dB may be considered every time the distance between the source and the recipient is doubled, provided that there are no sound reflective surfaces near the noise source.

b) Sound barriers shall be provided by placing buildings and occupancies less susceptible to noise between the source and the more susceptible ones.

c) For overall planning considerations, a noise survey shall be accomplished to examine all the possible causes of noise.

        4.4.3.1        Site Planning

a) Buildings of Occupancy A shall be located at a distance of at least  30 m from the roads with heavy traffic for example highways, where the external noise is 90 dBA or higher.

b) A distance of about 45 m or more shall be maintained between the building and the source of noise, where a greater relief from noise is desired.

c) Through traffic roads shall be excluded from residential areas.

        4.4.3.2        Orientation of Buildings  

a) The orientation of buildings shall  be planned in such a way as to reduce the noise disturbance from neighbourhood areas. Adequate setback of the building from the road shall be maintained in accordance with the provisions of Part 3.

If adequate distance between the building and the source of noise cannot be provided, rooms which do not need windows (or, windowless walls of habitable room) shall  face the source of noise.

b) Buildings which are not susceptible to noise may be used as noise baffles. These shall  be placed between the noise source and the quiet areas to be designed. Linear  blocks of buildings shall be built with the end facing noisy roads.

        4.4.3.3        Air Traffic  :  Requirements for acoustic design against aircraft noise are specified below :

a) No building for human occupancy shall be constructed where NEF value exceeds 40.

b) In case of development in areas near airports, adequate sound insulation shall be provided for buildings.

c) Educational institutions, hospitals, auditoriums etc. shall be located at places where the value of NEF is less than 25.

d) In areas exposed to less than 90 PNdB, all of the windows shall be closed and properly sealed, having double glazing, in order to provide an acceptable residential interior noise environment.

e) Industrial and commercial activities generating high interior noise environments may  be located in areas exposed to noise levels greater than 90 PNdB.

f) In airport areas of highest noise levels, relatively  sparsely manned sewage disposal plants, utility substations and similar other facilities may be located.

g) Approach and take off corridors shall be acquired so as not to impose unduly steep glide paths upon aricrafts.

        4.4.3.4         Road Traffic

a) The provision of adequate distance between the noise source and the recipient shall have to be maintained for efficient noise control measures.

b) Residential districts and special areas like hospital zones shall be segregated from expressways, highways, main streets, railways, playgrounds, industrial and commercial areas and airport.

        c)        i)        The external value of L10 shall be limited to a maximum of 70 dBA for zoning and planning new buildings in urban areas (when dwellings are proposed to have sealed windows).

                ii)        The maximum permissible upper limit of L10 shall be reduced to 60 dBA when the dwellings are proposed to have open windows.

                iii)        Major new residential developments shall preferably be located in areas with L10 levels substantially lower than those specified above.

                iv)        Where L10  is greater than 60-70 dBA, design solutions such as barrier blocks or noise buffers shall be utilized in order to reduce noise levels to at least  that level.

v) Some form of dwelling  insulation will have to be provided when the orientation of site or the density  of development does  not permit sound barriers.

vi) In the neighbourhood of residential, educational, institutional and health care buildings, legislative control shall be exercised in a bid to reduce or eliminate disturbing traffic noise particularly from buses, trucks and motor cycles, and the sounding of horns by all types of vehicles. Typical noise levels in free-flowing road traffic are given in Appendix I.

d) Greenbelts and plantations or artificial mounds may be used to reduce noise levels. Strong leafy trees shall be planted to act as noise baffles and shrubs or creepers to provide additional protection between tree trunks.

e) A comprehensive layout of traffic arteries shall have to be established by providing routes around (not through) the quiet surroundings like residential districts, schools, hospitals etc.

        4.4.3.5        Rail Traffic

a) No residential or public building (except for the railway station and its ancillary structures) shall be connected to the railway lines.

b) No mercantile or commercial buildings shall  abut the railway lines or the marshalling yards. Only planned industrial zones may be located beside the railway tracks.

c) In order to reduce the high noise levels, produced at the arrival and departure of trains, platforms in railway stations shall be treated with sound absorbing materials particularly on the ceiling.

d) The main platform floor shall be separated from the station building with a minimum gap of 50 mm so that the ground or structure borne vibrations are not transmitted to the building.

e) Less windows and other openings (as far as possible) shall be provided in the facade along the railway tracks.

f) Greenbelts and landscaping shall be developed along the railway lines. Thick belts of plantation, not less than 20 m in width may be provided.

g) A minimum distance of 50 m to 70 m between the buildings and the tracks shall be maintained where green belts and landscaping are developed.

h) Strong leafy trees shall be planted to act as noise baffles.

j) When a railway line passes close to habitable structures, residential buildings, highrise structures or apartments, emphasis shall be given to the problem of ground vibration transmitted to the buildings and proper isolation shall be installed for the critical areas.

4.5        General Noise Levels : INDOOR

4.5.1        Acceptable Indoor Noise Levels in Buildings

 The generally  acceptable noise levels  inside buildings  shall be below 20 dBA for auditoria and concert halls and 50 dBA for restaurants. The acceptable noise levels in other types of buildings shall be as shown in Table 8.4.1.

4.5.2        Planning and Design Considerations

        4.5.2.1        Buildings (or parts of buildings) which are considered to be especially susceptible to noise including hospitals, research laboratories, recording studios or the like should not be sited near sources of noise.

Table 8.4.1

Acceptable Intrusive Noise Levels

	dBA	NR		dBA	NR
Banks	50	40	Libraries, loan	45	35
Churches	35	25	Libraries, reference	40	30
Cinemas	35	25	Music rooms	30	20
Classrooms	35	25	Offices, private	40	30
Concert halls	30	20	Offices, public	50	40
Conference rooms	30	20	Open air theatres	40	30
Court rooms	35	25	Radio studios	30	20
Council chambers	35	25	Restaurants	50	40
Department stores	55	50	Recording studios	30	20
Flats, living	45	35	Shops	55	50
Flats, sleeping	35	25	Telephoning, good	50	40
Hospitals, wards	35	25	Telephoning, fair	55	45
Hotels, bedrooms	35	25	Television studios	35	25
Houses, living	45	35	Theatres	30	20
Houses, sleeping	35	25	Typing pools	55	50
Lecture rooms	35	25	Works canteens	60	55

        4.5.2.2        Buildings in which there are  some sources of noise shall have buffers separating the noise producing area from the other areas. The less vulnerable areas of the building may be planned to act as noise buffers.

        4.5.2.3        In the assessment of indoor noise levels, direct sound shall be separated from reverberant sound. As a general rule, the distance from the source to the recipient area shall be doubled to reduce the intensity of direct sound by 5 dB. The reverberant sound transmitted from one room to another shall be cut down by employing suitable sound absorption materials and by structural separation.

4.6        OCCUPANCY A : Residential Buildings

4.6.1        Sources of Noise

 Controlling  measures shall have to be taken against noise coming from outdoor and indoor sources as specified in Sec 4.4 and 4.5.

4.6.2        Planning and Design Requirements

        4.6.2.1        Space Layout  

a) Quiet and noisy quarters shall  be grouped and separated horizontally and vertically from each other by rooms (or spaces)  not particularly sensitive to noise such as entry, corridor, staircase, wall closets or other built-in building components.

b) A living room in one apartment shall  not be located adjacent to a bedroom in another apartment.

c) Bedrooms shall  be located in a relatively quiet part of the building and shall  not be adjacent to elevator shafts or mechanical rooms.

Bedrooms shall  not be planned alongside access balconies. Where the approach is  by an internal corridor, a sound baffle shall be provided by arranging bathrooms, dressing rooms or stores between the corridor and the bedrooms.

d) Bathrooms must  be separated acoustically from living rooms and shall not be planned over living rooms or bedrooms of the same dwelling or another.

Bathroom fixtures shall not be installed along walls which separate living room and bathroom.

Water closet shall  not be planned over living rooms and bedrooms, whether within the same dwelling or over other dwellings. Water closet cisterns shall not be fixed on partition next to bedrooms or living rooms.

e) Common walls between vertically staggered dwelling units transmitting footstep noises more easily into an adjacent unit shall be avoided.

        4.6.2.2        Sound Insulation Factors

a) Separation for Sound Insulation : The sound insulation criteria  in residential units are to be based on three grades :

i) Grade I criteria apply mainly to fully residential, quiet rural and suburban areas and in certain cases to luxury apartment buildings or to dwelling units above the eighth floor of a high-rise building.

ii) Grade II criteria apply to residential buildings built-in relatively noisy environments typical of urban or suburban areas.

iii) Grade III criteria express minimal requirements applicable to very noisy locations, such as commercial or business areas (like shop houses with dwelling units on the upper floors) or downtown areas.

Among the above three categories, Grade II covers the majority of residential constructions and shall therefore be regarded as a basic guide.

In all grades wall constructions and floor-ceiling assemblies between dwelling units shall have STC ratings at least equal to the values given in Table 8.4.2.

An STC rating of not less than 45 dB is to be provided in walls and floors of residential buildings,  between dwelling units of the same building and between a dwelling unit and any space common to two or more dwelling units.

Table 8.4.2

Airborne and Impact Sound Insulation Between Dwelling Units

Construction	Required Minimum Sound Insulation
	Grade  I	Grade  II	Grade  III
Walls	STC 55	STC  52	STC 48
Floor ceiling assemblies	STC 55	STC 52	STC 48

Service roof, storage areas, workshop, building maintenance room or garage serving more than one dwelling unit, shall be separated from the dwelling unit by a construction providing an STC rating of not less than 45 dB.

b) Reduction of Airborne Noise : In case of air borne noise (between the frequency range 100-31500 Hz), a sound insulation of 50 dB shall be provided in between the living room in one house or flat and rooms/bed rooms in another. The value shall be 35 dB in between different rooms of the same house. (See Appendix J for airborne sound insulation properties of walls, doors and windows).

c) Reduction of Airborne Noise Transmitted Through the Structure : Exterior walls shall be rigid and massive and have good sound insulation characteristics with as few openings as possible.

Ventilation ducts or air transfer openings (ventilators) where provided, shall be designed to minimize transmission of noise, if necessary, by installing some attenuating devices.

d) Construction of sound insulation doors shall be of solid core and heavy construction with all edges sealed up properly.  Hollow core wooden doors and light weight construction shall be avoided because these are dimensionally unstable and can warp, destroying the seal along the perimeter of the door.

Rubber, foam rubber or foamed plastic strips, adjustable or self-aligning stops and gaskets shall be used for sealing the edges of the doors. They shall be so installed that they are slightly compressed between door and stop when the door is in a closed position.  In simple cases the bottom edges shall have a replaceable strip of felt or foam rubber attached to minimize the gap between door and floor.

Separation between the two faces of the door shall be carried through uninterruptedly from edge to edge in both directions. Damping treatments shall be inserted between individual layers of the doors. Ordinary doors with surface leather padding shall not be used.

Automatic damped door closers are to be used whenever applicable and economically feasible  in order to avoid the annoying sound of doors slamming.

The difference between the TL of the wall and that of the door shall  not exceed 10 dB.

The floor of a room immediately above the bedroom or a living room shall satisfy the Grade I impact sound insulation.

4.7        OCCUPANCY B : Educational Buildings

4.7.1        Sources of Noise

        4.7.1.1        Outdoor Noise : Measures shall be taken in planning and design to control noise from external sources mentioned in Sec 4.4.

        4.7.1.2        Indoor Noise : The following sources of indoor noise shall be taken into consideration:

a) Wood and metal workshops, machine shops, technical as well as engineering testing laboratories, other machine rooms, typing areas etc. which produce continuous or intermittent noises of disturbing nature,

b) Music rooms,

c) Assembly halls, particularly those which are attached to the main building,

d) Practical work spaces, gymnasiums and swimming pools,

e) School kitchen and dining spaces,

f) Entry lobbies, foyer, lounge, corridors and other circulation spaces.

4.7.2        Planning and Design Requirements

        4.7.2.1        Site Planning :  The school building shall be located as far away as possible from the sources of outdoor noise such as busy roads, railways, neighbouring market places or adjacent shopping areas as well as local industrial and small scale manufacturing concerns.

 Where the site permits, the building shall be placed back from the street, in order to make use of the noise reducing effect of the increased distance between street line and building line.

 If adequate distance between the school/institution building and the noisy traffic route cannot be provided, rooms which do not need windows or windowless walls of  classrooms shall face the noisy road.

 Car parking areas shall  preferably be located in remote  parts of the site.

        4.7.2.2        Activities and Space Layout : The minimum requirement for sound insulation in educational buildings shall be as specified in Table 8.4.3.

        4.7.2.3        Halls and Circulation Areas : The lobby, lounge areas etc. or other circulation spaces and linking corridors shall be separated from teaching areas, lecture galleries or laboratories.  No direct window openings shall be placed along the walls of the corridors or circulation areas.

 Doors,  ventilators and other necessary openings shall be designed  with sufficient foam or rubber seals, so that they are noise proof when closed.

        4.7.2.4        Noise Reduction within Rooms :  Lecture halls of educational institutions (with a seating capacity of more than 100 persons) shall be designed in accordance with the relevant acoustical principles.

        Lecture halls with volumes of up to about 550 m3 or for an audience of up to about 150 to 200, shall not require a sound amplification system, if their acoustical design is based on appropriate principles and specifications.

 A diagonal seating layout shall preferably be used for rectangular lecture rooms of the capacity mentioned above as it automatically eliminates undesirable parallelism between walls at the podium and effectively utilizes the diverging front walls as sound reflectors.

Table 8.4.3

Minimum Requirements of Sound Insulation for Different use

in Educational Buildings

Noise Producing Characteristics	Type of Use	Minimum Sound Reduction (dB)
Noise producing	Workshops Kitchens Dining rooms Gymnasiums Indoor swimming pools	25
Noise producing but requiring silence at times	Assembly halls Lecture halls Music rooms	45
Average noise producing	General classrooms Practical rooms Laboratories Offices	35
Rooms requiring silence	Libraries Studies	35
Rooms requiring privacy	Medical rooms Staff rooms	45

4.8        OCCUPANCY D :  Health Care Buildings

4.8.1        Sources of Disturbing Noise

        4.8.1.1        Outdoor Noise : Sources of outdoor noise specified in Sec 4.4 shall be taken into consideration for planning and design. Additionally, health care service facilities like ambulance, medicine and equipment vans, store deliveries, laundry and refuse collection trolleys are also frequent sources of noise. Health care buildings shall be sited away from such sources as far as practicable.

        4.8.1.2        Indoor Noise  :  Indoor noise  sources include mechanical and mobile equipment like X-ray and suction machines, drilling equipment etc.

 Planning and design shall take into account the following sources of noise :

a) The handling of sterilizing, as well as metal or glass equipment,

b) Wheeled trolleys used for the purpose of carrying foods and medical supplies,

c) Mechanical equipment like mechanical and electrical motors, machineries, boilers, pumps, fans, ventilators, transformers, elevators, air-conditioning equipment etc.

d) Operational facilities like refrigerators, sterilizers, autoclaves etc. ,

e) Patient service facilities including oxygen cylinders or tanks, saline stands, carrier carts and instrument cases, etc. ,

f) Maintenance work of engineering services like plumbing and sanitary fixtures or fittings, hot and cold water and central heating pipes, air-conditioning ducts, ventilation shafts etc., and

g) Audible calling systems, radio and television sets.

4.8.2        Planning and Design Requirements

        4.8.2.1        Site Planning :  Site shall be selected to keep adequate distance from traffic noise from highways, main roads, railroads, airports and noise originating from parking areas. In addition to the requirements of  Sec 4.4.3, the following requirements shall  be fulfilled :

a) In the selection of a site and site planning, consideration  shall be given to:

i) Distance from exterior noise,

       ii)   Effect of high buildings adjacent to the site which can act as noise reflectors, and  

iii) Traffic conditions surrounding the site.

b) Parking areas shall  be carefully located at the farthest possible corners of the premises. If enough space is not available to provide facilities for the desired number of vehicles, parking spaces shall be provided in more than one area.  Loading platforms and service entries are to be planned in such a manner  as to minimize noise in areas requiring silence.

c) Closed courts shall preferably  be avoided.

        4.8.2.2        Activities and Space Layout : The following points shall be given due consideration in  the planning and design of health care buildings.

a) Rooms to be used for board meetings, conference, counselling and instructional purposes shall be grouped near public zones of the building in such a way that spread of noise can be avoided.  

b) Long corridors shall be avoided.

c) The main kitchen shall  be housed in a separate building and connected to the wards only by service lifts or a service stair. If this is impracticable, it shall be planned beneath the wards, rather than above them.

d) Mechanical plants shall preferably be placed in separate buildings.

e) Rooms housing equipment, operational facilities and patient service facilities shall  be designed for adequate sound insulation.

f) Closed courts shall be avoided, unless rooms facing the court are air-conditioned with completely sealed and air tight windows.

g) The units which are themselves potential sources of noise for example, children's wards and outpatient departments, shall  be treated with special care regarding the protection against noise.

        4.8.2.3        Noise Reduction in the Sensitive Area  :  In health care buildings, many sensitive areas such as operation theatres, doctor's consultation rooms, intensive care units and post-operative areas shall be provided with special  noise control  arrangements.

 These rooms shall preferably be isolated in locations (or corners) surrounded by other intermediate zones which ensure protection of the core area from outdoor noise.

 A sound reduction of about 45 dBA between  the consulting  and the waiting  rooms shall be provided in order to weaken the transmission of sound.

 A lobby like space in between the interconnecting and communicating doors shall be provided.

        4.8.2.4        Sound Insulation Factors :  The rooms and indoor spaces of a health care building, shall be treated with sound absorptive materials.

 Different STC ratings of walls  specified for separate components of buildings shall have to be considered as follows :

a) For airborne noise, the average STC rating of wall and floors shall be 50 dB.

b) An STC rating of 55 dB shall  be required between rooms whose occupants are susceptible to noise.

c) In general an average STC of 45 dB is to be provided  for corridor walls and for walls between patient rooms.

d) All doors shall  be fitted with silent closers. Doors  to opposite rooms, shall be positioned in a staggered manner.

e) For ward doors, a corresponding STC of  35 dB shall be provided.

f) PVC mats, rubber mats or other resilient materials and rubber shod equipment shall  be used in utility rooms, ward kitchens and circulation areas as floor coverings.

Other finish materials like  rubber tile, cork tile, vinyl tile or linoleum which can also help reduce the impact noise substantially shall be used alternatively.

g) Mobile equipment, such as trolleys and bed, oxygen cylinder carriers and stretchers shall  be made relatively silent by means of nonfriction rubber tyred wheels .

h) Special treatments such as thin nonporous coverings or films over some soft absorbent materials shall be used for  good sound absorption when a washable acoustical treatment is desired.

i) Door and window curtains or screens, as well as bed sheets etc. shall be used wherever the indoor openings are located to help reduce reverberation in the hard surfaced surroundings. Curtain rails, rings and runners of silent type shall be used so that they  generate as little frictional noise  as possible.

j) Ventilation ducts and conduits shall  be laid out in such a way that they  do not open an easy by-pass for spreading out any noise from other sources. These conduits and ducts  shall  be completely sealed around the pipes where they pass through walls and floors.

k) Special care shall be taken to reduce noise of plumbing equipment and fixtures. Specially made silencing pipes and flushing fixtures  shall be used to reduce the noise of water closet and cisterns in lavatories and toilets.

Ducts carrying waste or water pipes shall be properly lined with sound insulation material to prevent noise from the pipes passing through duct walls into the patients' wards or cabins or the spaces susceptible to noise.

l) Wherever available, cisterns  shall be used to replace the pressure  operated flushing system so that the disturbance becomes less irritating.

4.9        Occupancy E : Assembly

4.9.1        General  

 Buildings of Occupancy E shall be designed both for transmission of noise through the walls and openings and also for internal acoustics. Public address systems installed in such buildings shall conform to the specifications of Sec 4.12.2.

4.9.2        Sources of Noise

        4.9.2.1        Outdoor Noise  :  The following sources of noise shall be taken into account in planning and design:

a) Traffic noise (air, road and rail) and noise from other outdoor sources entering through walls, roofs, doors, windows or ventilation openings,

b) Noise from any other gathering spaces, public meetings, outdoor activities and crowds, particularly during the time of breaking of shows and performances,

c) Noise produced from parking areas.

        4.9.2.2        Indoor Noise : The following indoor noise sources shall be taken into account in planning and design :

a) Noise from other adjacent halls located within the same building used for similar performance, or  for seminar, symposium or general meetings,

b) Noise produced from ticket counters, lobby or lounge areas, rehearsal rooms, waiting areas and corridors,

c) Noise generated from other ancillary services located within the building, like cafeteria or snack bar, tea shop, post office, bank or the like,

d) Noise generated from the mechanical or electrical equipment, air-conditioning plants, ventilation channels and ducts, plumbing and water lines etc.

4.9.3        Planning and Design Requirements

        4.9.3.1         Site Planning and Acoustical Requirements : The noise control of auditoria or assembly halls shall begin with sensible site planning following the measures and precautions stated below :

a) The auditorium shall be effectively separated from all exterior and interior noise and vibration sources as far as practicable;

b) The assembly halls shall be protected from vehicular or air traffic, parking or loading areas, mechanical equipment, electrical rooms or workshops.

 The following are the acoustical requirements for good hearing conditions in an auditorium which shall be ensured in planning and design :

a) Adequate loudness shall have to be ensured in every part of the auditorium;

b) The sound energy shall be uniformly distributed in the hall;

c) Optimum reverberation characteristics shall have to be provided;

d) The hall shall be free of such acoustical defects as echoes, long delayed reflections, flutter echoes, sound concentrations, distortions, sound shadow and room resonance etc.;

e) Noise and vibration shall be excluded or reasonably reduced in every part or the hall room.

        4.9.3.2        Activities and Space Layout in Divisible and Multi-purpose Auditoria

a) A protective buffer zone of rooms between exterior noise source and auditorium proper shall be designed.

b) Rooms in the buffer zone (lobbies, vestibules, circulation areas, restaurants, ticket counters, offices etc.) shall  be  shut off from the auditorium proper by sound insulation doors.

c) The purposes of the subdivided spaces shall be clarified, in order to establish the predictable intensity of the various sound programmes.

        4.9.3.3        Noise Reduction within Rooms

a) There shall not be any use of continuous, unrecognizable and loud background noise.

b) The ventilating and air-conditioning system shall  be so designed that the noise level created by the system is at least 10 dB below the permissible background noise level specified in noise criteria level.

c) In order to protect the hall from external noise the minimum sound reduction value required in an auditorium is 65 dB for a concert hall and 60 dB for a theatre. This reduction shall be provided on all sides.

        4.9.3.4        Sound Insulation Factors

a) Rooms in the buffer zone (lobbies, vestibules, circulation areas, restaurants, counter and issue desk corners, office etc.)  shall have sound absorbing ceilings and carpeted floor. If the rooms are to be used for the purposes of verbal instructions only, a moderate degree of sound insulation (STC 40 to 45 dB) shall be accomplished by the movable partitions.

b) If audio equipment or loudspeakers are to be used, an acoustically more effective, efficient partition system shall  be used, with sound insulation of STC 45 to 50 dB.

c) An insulation of STC 50 to 60 dB shall be provided if any section of the space is selected for the performance of live music.

d) All windows shall have to be eliminated from the main auditorium walls in order to exclude excessive outdoor noises.

e) Suspended ceilings shall accommodate the ventilating, air-conditioning and electrical services above the room.

f) In order to increase the effectiveness of the suspended ceilings the following measures shall be taken :

        i)        The ceiling membrane shall weigh not less than 25 kg/m2;

ii) The ceiling membrane shall not be too rigid;

iii) Noise transmission through  the ceiling shall have to be avoided by the use of a solid, airtight membrane;

iv) Gaps between ceiling and surrounding structure shall be sealed;

v) The air space between ceiling membrane and structural floor shall be increased to a reasonable maximum;

vi) An absorbent blanket is to be used in the air space above the ceiling;

vii) The number of points of suspension from the structural floor above shall be reduced to a minimum;

viii) Hangers made of resilient substance shall be preferable to the rigid ones.

g) In order to improve the airborne or impact sound insulation of a ceiling the following specifications shall be followed :

i) The ceiling membrane shall have a minimum of 25 mm solid cement plaster layer with completely closed, airtight and sealed joints all around;

ii) If further reduction of undesirable noise is desired within a sound insulated room, sound absorptive treatment shall be provided along the underside of the solid ceiling.

        4.9.3.5        Masking Noise :  The artificial noise produced by electronically created background noise for the purpose of drowning out or masking unwanted noise, shall be provided. The process shall effectively suppress minor intrusions which might interrupt the recipient's privacy.

 The maximum permissible background noise levels in various occupancies is specified in terms of noise criteria (NC) curves. Each of the NC curves is expressed by the sound pressure level values in the important 1200-2400 Hz frequency band. The NC levels shall be used to specify the desirable lowest limit under which the background noise must not fall. (See Appendix K for details).

        Note :         The general configuration of the NC curves is quite similar to the noise rating (NR) curves established by the International Organization for Standardization, used mostly in the European practice

4.10 OCCUPANCY F : BUSINESS AND MERCANTILE BUILDINGS

4.10.1        General

        Buildings of Occupancy F shall be planned and designed to minimize noise from external and internal sources.

4.10.2        Sources of Disturbing Noise

        4.10.2.1        Outdoor Noise : The following sources of outdoor noise and those specified in Sec 4.4 shall be taken into account in the planning and design of business and mercantile buildings :

- Traffic,

- Playgrounds,

- Market places and shopping areas,

- Crowds grouped around the buildings for business purpose or other.

        4.10.2.2        Indoor Noise : The following sources of indoor noise shall be identified for noise attenuation within buildings :

a) Mechanical noise, caused by heating, ventilating and air-conditioning systems, elevators, escalators and pneumatic tubes etc. ;

b) Noise produced by office equipment or  machines such as typewriters, printers, teleprinters, reproduction, tabulating and punching machines etc.;

        c)        Noise produced by mechanical amplifiers, for example in seminar halls, conference rooms or staff training rooms or the like where public address system is used;

d) Machine noise  generated from slide rooms, projection rooms and from electrical and mechanical machines like generators, transformers, switch rooms and electric substations etc. ;

e) Typical office noise created by speech, voices in circulation areas, opening and closing of doors etc. ;

f) Plumbing systems, ventilation plants, lift machineries, air-conditioning and cooling systems.

4.10.3        Planning and Design Requirements

        4.10.3.1        Site Planning  : Rooms susceptible to noise shall be located away from the sources of noise.

        4.10.3.2        Activities and Space Layout : Spaces producing noise and those susceptible to noise shall be separated as far as practicable. The effective length of long corridors shall  be minimized. Swing doors are to be provided at intervals.

        4.10.3.3        Noise Reduction in the Sensitive Areas

a) Open plan Offices

i) The floor area may  be carpeted in order to absorb airborne noise and footstep noise. The carpet shall preferably be thick and placed on top of resilient floors.

ii) The entire portion of the ceiling shall be treated with sound absorption materials. Such treatment shall be applied to the screens and nearby walls also.

A highly sound absorptive ceiling with a sound absorption coefficient of 0.70 shall preferably be used to absorb 70 per cent of the sound energy  reflecting 30 per cent of it.

iii) Moderately noisy office equipment (like typewriters, telephones, computers etc.) shall be distributed as uniformly as possible all over the office space.

iv) Noisy office equipment shall be concentrated into specific areas of the office space. The space shall  be treated with maximum amount of sound absorptive material and visually separated from the rest of the office.

b) General Offices : Sound absorbent ceiling  shall  be provided in corridors. Hard floor finishes and batten floors in corridors shall be avoided. Floor ducts shall  be planned on one side of corridors.

        4.10.3.4        Reduction of Noise at Source : The following measures shall be undertaken to reduce noise at source depending on the degree of noise reduction desired.

a) The noise from slamming of doors shall be reduced by fitting automatic quiet action type door closers. Continuous soft, resilient strip set into the door frames as well as quiet action door latches shall be used.

b) Machines like typewriters, calculators, printers etc. shall be  fitted or installed with resilient pads to prevent the floors or tables (on which they stand) from acting as large radiating panels.

c) Noises from ventilating systems, from a uniform flow of traffic or from general office activities,  shall be considered  to generate an artificial masking noise. In open plan offices the provision of a relatively high but acceptable degree of background noise (from the ventilating or air-conditioning system) shall be provided, in order to mask undesirable office noises created by typewriters, telephones, office machines or loud conversation and to provide a reasonable amount of privacy.

The background noise masking system shall be introduced gradually without  disturbing the feeling of the occupants.

The air-conditioning system may be used to generate background masking noise if the noise level from the ceiling fans, ducts etc. can be suitably reduced to generate the desired frequency spectrum.

        4.10.3.5        Sound Insulation Factors : The acoustical performance of the partitions dividing rentable office spaces shall not exceed an STC rating of 25 to 30 dB, unless the background noise is so high that it masks the sound coming through the lightweight partition.

 If lightweight partitions are employed  for subdivision of large spaces into executive cabins and secretarial areas, the following measures shall  be taken  to increase the insulation factors:

a) Sound barriers shall be provided up to above the false ceiling with a noise reduction characteristic that will not be affected by ducts, conduits or other cable lines including electricity and water pipings installed in the ceiling space.

b) Where construction of light weight partitions is considered essential, a double skin panel shall be preferred.

The panels shall  be installed apart from each other either by use of separate framing or by  use of elastic discontinuities in the construction. Sound absorbing materials  shall be provided in the air cavity between the panels   so that more insulation can be assured.

c) All apertures, gaps and joints at side walls, floors and ceiling junctions shall be properly sealed.

d) A double panel hollow floor construction shall  be employed with heavy sound damping materials introduced between the panels for effective reduction of the structure borne noise transmitted from upper floors to the floors below, particularly  when lightweight floors are provided in multi-use spaces.

Lightweight materials having high natural frequencies  may resonate or vibrate due to an applied vibratory force  which may be  caused by mechanical equipment, road or rail traffic etc.  These materials,  if used for specific reasons, shall  be isolated from the source of noise in order to reduce the amount of vibration transmitted to the building.

e) The floor surfaces surrounding the office space may be lined with a carpet of high sound absorption.

f) For sound adsorption with floor carpeting, the following characteristics shall be maintained:

i) Fibre type  carpet shall not be used, as it has practically no effect on sound absorption;

ii) Hair, hair jute and foam rubber pads  shall be used for  higher sound absorption than the less permeable rubber coated hair jute, sponge rubber etc.;

iii) To improve sound absorption the loop-pile fabrics with increased pile height (with the density held constant) shall be applied;

iv) The backing shall be more permeable for  higher sound absorption.

4.11 Occupancy G : Industrial Buildings

4.11.1        General Noise Levels

 In the noise control of industrial buildings the following requirements are to be fulfilled:

a) An acceptable  acoustical  environment for individual workers and machine operators ;

b) Speech communication among operators to the required degree ;

c) Protection of other workers or office employees (either close to the noise source or at some other location within the same building) ;

d) Prevention of noise transmission into adjacent buildings or into the surrounding community.

        4.11.1.1        Intermittent Noises :  Intermittent noise in the form of isolated explosions, and periodic  noise related to pressure relief valves, hammering, grinding and sawing operations etc. shall be identified for enforcing controlling measures.

        4.11.1.2        Sources of Noise : The following sources of noise in industrial buildings and manufacturing plants shall be identified and investigated to find whether the machines are in smooth operation and producing minimal mechanical noise.

a) Fabrication and assembly machines;

b) Machines used for  material transport and general plant services;

c) Noise caused by impact and coupled with resonant response of the structural members, connected to the impacting surfaces;

d) High frequency sounds generated from grinders;

e) Frictional noise occurring at the time of sawing, grinding or sanding, as well as during the cutting on lathe machines and in brakes or from bearings;

f) Noise  generated  from piping systems and valves;

g) High velocity flow of air, steam or other fluids that undergo an abrupt change in pipe diameter  which  give rise to turbulence and resultant noise, and  noise  generated by rapid variation in air pressure caused by turbulence from high velocity air, steam or gases;

h) Unpleasant noise identified with rotating or reciprocating machines, which is generated due to pressure fluctuation in the fluids inside the machines.  

4.11.2        Hearing Damage Risk Criteria

 When the sound level at a particular section in a factory  or industrial building exceeds the specified level in terms of magnitude and time (as shown in Table 8.4.4 below), feasible engineering control shall be applied and implemented in order to reduce the sound to the limits shown.  Personal  hearing protection equipment shall be provided and used  if such control  fails to reduce sound levels.

4.11.3        Interference with Communication

 In industries where the operator has to follow verbal instructions during operation of the machine the background noise shall be reduced to an acceptable level.

 Precautionary measures shall be taken so that the noise generated inside may not be the cause of accidents by hindering communication or by masking warning  signals.

4.11.4        Requirements for Noise Reduction

        4.11.4.1        Noise Reduction by Layout and Location : Considerable noise reduction may be achieved by a sensible architectural layout in noisy industrial buildings following the steps mentioned below :

a) Noisy areas shall be separated from spaces requiring silence.

b) The office block is to be located in a separate building. If this is not possible, the office space in a factory shall be segregated from the production area as far as practicable.

c) The office building shall not have a common wall with the production areas. Where a common wall is unavoidable it should be of heavy construction (not less than 375 mm thick).

d) Electrically operated vehicles shall be used as far as practicable, since they eliminate most of the noise normally  associated with combustion engines.

Table 8.4.4

Permissible Exposure Limits For  Steady-State Noise

Sound Level dBA	Time Permitted hour - minute
85 86 87 88 89 90	16-00 13-56 12-08 10-34 9-11 8-00
91 92 93 94 95	6-58 6-04 5-17 4-36 4-00
96 97 98 99 100	3-29 3-02 2-50 2-15 2-00
101 102 103 104 105	1-44 1-31 1-19 1-09 1-00
106 107 108 109 110	0-52 0-46 0-40 0-34 0-30

        4.11.4.2        Noise Reduction at Source :  In order  to suppress the noise at the source relatively silent machines and equipment shall be installed. Additionally the following provisions shall be adhered to :

a) Appropriate type of manufacturing process or working method shall be selected which does not cause disturbing noise. Machine tools and equipment are to be selected carefully in order to attain lower noise levels in the machine shop.

b) Maintenance of vibrating and frictional machineries shall be ensured.

c) Impact noises in general shall be reduced; soft and resilient materials shall be applied on hard surfaces where impact noise can originate.

d) Rubber tyres or  similar other materials shall be fixed on the areas or surfaces used for the handling and dropping of materials.

e) The area of the radiating surface from which a noise is  radiated shall  be reduced to a minimum.

f) Resilient flooring (carpeting, rubber tile, cork tile, etc.) shall be used adequately to reduce impact transmission onto the floor .

g) Flexible mountings, anti-vibration pads, floating floors etc. shall be used to prevent the transmission of vibration and shock from various machines into the building or structure.

h) Mechanically rigid connecting paths must be interrupted by resilient materials so that the transmission of vibration and noise is reduced.

 4.11.4.3  Isolator Specifications

a) Isolators shall be made of resilient materials like steel (in the form of springs), soft rubber and corks.

b) Direct contact between the  spring and the supporting structure shall  be eliminated, in order to reduce transmission of high frequencies by metal springs.

c) Rubber or felt pads shall be inserted between the ends of the springs and the surfaces to which they are fixed.

d) Felt or cork shall be used under machine bases, as resilient mats or pads.

e) If the equipment is massive like drop hammers causing serious impact vibration (in larger manufacturing plants), it  shall be mounted on massive blocks of concrete, on its own separate foundation.

f) The foundation shall  have a  weight 3 to 5 times  that  of the supported machines.

g) A sound reduction of 5 to 10 dBA shall have to be realized from the vibration isolation measures.

        4.11.4.4        Noise Reduction by Enclosures and Barriers : When the plant is large  in which the overall noise level results from many machines, an enclosure shall be provided.

a) When only one or two machines are the dominant source of disturbing noise, the noisy equipment shall  be isolated in a small area of enclosure.

b) The enclosure shall be in the form of close fitting acoustic box around the machines. The box shall be of such character that  the operator can continue with his normal work outside the box.

c) An enclosure around the offending unit shall be impermeable to air and lined with sound absorbing materials  such that the noise generated by machines is reduced substantially.

d) i) When the industrial plant is a large one in which the resultant noise level is produced from a number of machines, enclosures shall be used either for supervisory personnel or operators who are engaged in monitoring the automatic machines. Such barriers may have inspection openings.

ii) Enclosures of this type shall ensure noise reduction of at least  30 dBA, and shall be made of sheet metal lined inside with an appropriate insulation material.

iii) Where curtains are used to isolate the noisy equipment in a small area, they shall  be of full length i.e. from ceiling to floor and shall be made of fibreglass cloth and lead or leaded vinyl.

e) If the size of the machine is large and asks for more working spaces, thus not permitting close fitting enclosures, the machine shall be housed in a separate room or enclosure.

The inside of the enclosure shall be lined with sound absorbing materials in order to reduce the contained noise.

f) If after all these measures are taken the noise level still remains above a tolerable degree, the workers shall be provided with earplugs for protection.

4.12 Acoustical Requirements of Special Occupancies

4.12.1        Susceptible Buildings

        4.12.1.1        Recording and Radio Studios :  A recording studio shall present optimum acoustic conditions. A differentiation shall be made among the  numerous various purposes of studio use.

a) Particular attention shall be given to the following  requirements :

i) An optimum size and shape of the studio shall be established following the design criteria;

ii) A high degree of diffusion shall be secured;

iii) Ideal reverberation characteristics shall be provided;

iv) Noises and vibration shall be completely eliminated and acoustical defects shall be totally prevented.

b) The acoustical treatments shall be uniformly and proportionately distributed over the three pairs of opposite surfaces enclosing the studio.

c) Portable acoustic screen and a reverberation chamber shall be provided so that the  desired reverberation condition can be achieved.

d) Variable absorbers such as hinged or sliding panels, rotatable cylinders, adjustable drapery etc. shall be fixed on wall surfaces and ceiling areas.

e) All surfaces shall  be carefully checked for echoes, flutter  echoes etc.

f) Parallel surfaces shall be eliminated or treated with highly absorptive acoustical materials (throughout the frequency range between 63 and 8000 Hz).

        4.12.1.2        Research Laboratories

a) In the selection of site, care shall be taken to ensure that no noise generating installations exist in the vicinity.

b) Location of laboratories shall  be secluded from the noisy zones within the building.

c) A sound insulation of at least 35 dB shall be achieved by means of  acoustical partitions where offices are attached to the laboratory.

d) Sound absorbing screens shall  be used where scientists and researchers are engaged in laboratory activities and desk work simultaneously.

e) Transmission of noise through service ducts, pipes, lifts and staircases shall  be guarded.

f) Double glazed windows shall  be provided in the noise sensitive areas. There shall be a minimum gap of 100 mm  between the two glasses.

        4.12.1.3        Music Rooms : The following provisions shall apply to music rooms, including rehearsal rooms, instructional space, practice booth etc.

a) Acoustical conditions in practice booths and listening booths shall have a reverberation time of  0.4 to 0.5 second.

b) Adequate floor area, room height, room shape and volume must be established to achieve proper reverberation.

c) Sound absorbing materials shall be applied sufficiently so that the excessive sound generated by bands or individual instruments can be soaked up.

d) Parallelism between opposite surfaces shall be avoided.

e) Entire surfaces of  at least two adjacent walls, and all the ceiling area shall  be treated with sound absorbing materials.

f) Use of suspended ceiling shall be avoided.

g) The underside of the floor construction above shall be exposed and treated acoustically to provide adequate sound insulation.

h) Ventilating and air-conditioning ducts shall not transmit undesirable sounds of music from one space to another, horizontally and vertically.

        4.12.1.4        Libraries : A quite and peaceful interior shall be maintained inside libraries. The following provisions are to be  adhered to in planning and design:       

a) Most of the cubicles area shall  be located around the central portion of the library building.  Baffle lobbies shall be planned between the library  and corridors.

b) Screening and sound insulation measures shall be undertaken in and around the reception/issue desk  and photocopying facility areas.

c) Stack rooms, store rooms and administrative offices shall be planned in such a way that the audiovisual areas are properly  isolated from external noises.

d) Walls enclosing the library shall have a sound reduction value of not less than 50 dB.

e) Fanlights shall be double glazed and nonopenable.

f) Walls facing the corridors or other noisy areas shall not have fanlights or borrowed lights unless they are double glazed.

        4.12.1.5        Law Courts and Council Chambers

a) Entrance into court rooms and council chambers (especially from circulation areas and gathering spaces) shall be through baffle lobbies, with two sets of doors fitted with silencers.

b) Offices shall be planned around the court rooms or chambers for further protection against outdoor noise and the central rooms shall have a sound insulation value of not less than 50 dB (provided by 225 mm thick brick wall) to insulate against airborne noise in the corridors.

c) The court and chamber rooms shall have floors finished with resilient materials.

d) Ceiling and upper parts of the walls of lobbies and circulation areas shall have sound absorbing treatments.

4.12.2        Public Address System

        4.12.2.1        Design of public address systems shall be performed by an engineer according to standard engineering practices. The design shall take care of equipment choice, positioning of the individual elements and other precautions to obtain optimum performance of the system.

        4.12.2.2        Passenger terminals and other public places equipped with public address systems shall as far as practicable avoid the use of sound reflecting surfaces like hard walls and floors. Reverberation time shall be reduced as far as possible by using sound absorbing materials on walls and ceilings.

        4.12.2.3        Reverberator built-up sound level shall not be relied upon. Direct sound shall preferably be audible in all areas to be covered by the public address system.

        4.12.2.4        Sound levels of the public address system in the areas covered shall be adequately high to overcome background noise.

Related Appendices

Appendix D Relationship of Weighting Curves for Sound Levels

Appendix E Recommended Optimum Reverberation Time for Assembly Buildings

Appendix F STC Ratings of Walls and Floors

Appendix G Air Traffic Noise Levels

Appendix H Frequency Values and Noise Levels of Some Common Sources

Appendix I Typical Noise Levels in Free-Flowing Road Traffic

Appendix J Average Airborne Sound Insulation of Common Constructions

Appendix K Recommended Background Noise Criteria and NC Curves