41 Sound CI/SfB: (P) UDC: 534.84 Uniclass: U37
Neil Spring of Sandy Brown Associates Updated by Chris Steel of the Robin Mackenzie Partnership, building acoustics consultants KEY POINTS: Current Building Regulations in England and Wales now require completion testing or registration with a recognized provider as proof of compliance Insulation requirements now extend to include school design in England and Wales
• •
Contents 1 Introduction 2 Fundamental acoustics 3 Room shape and quality 4 Noise 5 Sound insulation 6 Acoustical test data 7 Standards and codes of practice 8 Legislation 9 Bibliography
1 INTRODUCTION Sound affects the occupants of a building in two distinct ways:
sound, not the amplitude or peak value A. This is because the rms value is the best measure of energy whether the sound is a pure tone or not. pffiffiffi For a sine wave, the rms value is the amplitude divided by 2: Audible sound pressures extend approximately from 2 10–5 Pa (the quietest sound that most people can hear – the threshold of hearing) to 100 Pa (sound so loud that it starts to be actually painful). This enormous range is telescoped by using a logarithmic notation employing the decibel. The sound power of a pure tone is proportional to the square of the pressure. The ratio of the powers of two sounds is therefore the square of the ratios of the pressures. The sound pressure level, Lp of a given sound expressed in decibels is ten times the common logarithm of the ratio of its power and that of the internationally recognised threshold of hearing: i.e. 2 p1 p21 Lp ¼ 10 log10 2 ¼ 20 log10 decibels ðdBÞ 2 10 – 5 p0 Expressed in this way, the audible range extends roughly from 0 dB SPL to 134 dB SPL. A sound usually seems twice as loud when its pressure has trebled, i.e. it has increased by 10 dB.
quality of sounds generated within, e.g. a concert hall • The Annoyance with loud noise. (Noise is a term used to describe • unwanted sound.) The factors that determine sound quality are still imperfectly understood, despite much recent research and experience. The same is true to a lesser extent of the factors affecting noise. Part of the difficulty is that asking someone how he feels about his environment may itself modify his reactions. Very loud prolonged sounds, such as occur in some industries, can result in permanent damage to the ear. The fear that they can damage buildings has been exaggerated, and need not normally be considered by the architect. Many acoustical problems in buildings can be avoided by considering the broad requirements early in the design process. Later on, rectification is rarely satisfactory or economical. Changes to the building regulations in England and Wales has increased the level of expectation in achieving the minimum sound insulation criteria set out in the Building Standards regulations and now includes acoustic comfort in communal areas, noise control in domestic like areas (i.e. halls of residents) and suitable acoustic standards in schools. These changes have increased need for designers to be aware of acoustics but also to be more aware of when the services of a qualified acoustic consultant are required.
2.02 Sound power level The sound power of a source, measured in Watts, is deduced from measurements of sound pressure in a well-defined acoustical environment, such as an anechoic chamber or a reverberation room. The range of powers being even greater than that of pressure levels, decibel notation is again used. The international reference level for sound power is 1 pW, so the sound power level Lw is given by W1 Lw ¼ 10 log10 dB 10 – 12 where W1 is the sound power in Watts. The SPL produced at a particular place will depend on the distance, orientation and sound power level of the source; and also on the amount of acoustical absorption present. It is important in any application to distinguish between sound pressure level and sound power level as they are usually numerically quite different.
2 FUNDAMENTAL ACOUSTICS Sound is perceived when the eardrum is set vibrating by variations in the air pressure just outside the ear. These pressure variations will have been caused by some vibrating object, said to radiate sound. The simplest kind of sound is a single pure tone, for which the graph of air pressure plotted against time produces a sine wave, 41.1. The greater the amplitude A of the pressure variation, the louder the tone. The more rapid the variation (i.e. the higher the frequency), the higher the pitch of the tone. 2.01 Sound pressure level The sound pressure of a pure tone generally means the root mean square (rms) value of the variation in pressure of the air due to the
41.1 Sinusoidal variation of air pressure at a point, due to a pure tone 41-1
41-2
Sound
2.03 Frequency The frequency of a pure tone is measured in hertz (Hz), equal to and formerly called cycles per second, 41.1. The human range of audible frequencies varies, but is roughly from 20 to 20 000 Hz. The ability to hear higher-frequency sounds progressively deteriorates with age. Any steady sound, however complex, can be reproduced by combining enough pure tones of the right amplitudes and frequencies. Thus, if we know the behaviour of a material, wall or room, etc. with regard to the audible spectrum of pure tones, we can predict the behaviour with any steady sound. The acoustical properties of materials or rooms are described in relation to contiguous frequency bands. Octave-band measurements are carried out where economy is needed. One-third octave bands are used when greater accuracy is required. Octave-band centre frequencies: 63, 125, 250, 500, 1000, 2000, 4000 Hz One-third-octave band centre frequencies: 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300, 8000 Hz
2.04 Reverberation time The reverberation time is defined as the time taken for an interrupted sound to fall in level by 60 dB. The reverberation time and its variation with frequency is probably the most significant measurable factor determining the acoustical character of a room and it can be calculated from Sabine’s formula T¼
0:16 S þ xV
where V ¼ room volume in m3 S ¼ total surface absorption in m2 x is a coefficient related to the sound attenuation of air. The total surface absorption is obtained by adding together the separate areas of absorbent: Sa ¼ S1 a1 þ S2 a2 þ S3 a3 þ þ Sn an where S1 is the area in m2 with absorption coefficient 1, etc. Table I gives examples of typical absorption coefficients. The Norris–Eyring formula is accepted as more accurate for rooms with a high average absorption coefficient T¼
0:16V S½ – 2:30 logð1 – Þ þ xV
The range of T varies from 0.25 s for a small pop recording studio, to over 10 s for a large cathedral. For clear speech in a lecture hall or theatre, T should be between 0.7 and 1.0 s. Outside these limits, a specially designed speech reinforcement system will be required.
Table I Absorption coefficients Frequency Hz 63
125
250
500
1000
2000
4000
Air, x (per m3)
0
0
0
0
0.003
0.007
0.023
Audience seated in fully upholstered seats (per person) m2
0.15
0.18
0.40
0.46
0.46
0.51
0.46
Orchestral player with instrument (average), m2
0.18
0.37
0.8
1.1
1.3
1.2
1.1
Carpet, pile over thick felt on concrete floor
0.05
0.07
0.25
0.5
0.5
0.6
0.65
Plaster, on solid backing
0.05
0.03
0.03
0.02
0.03
0.04
0.05
For most uses, the reverberation time should be the same for low, middle and high frequencies. A moderate rise in the bass reverberation time is acceptable for speech, and is often considered preferable for music. In large auditoria, the high-frequency reverberation time inevitably falls because the enclosed air has a high absorption value. In any case, allowance must be made for the absorption of the audience, usually the greatest single component. The acoustical shortcomings inevitable in multi-purpose auditoria can be alleviated by installing an electro-acoustic enhancement system such as the assisted resonance system at the Royal Festival Hall in London. A variety of competing systems are now available.
3 ROOM SHAPE AND QUALITY 3.01 Preferred dimensions – large auditoria The size of a room is usually determined by factors other than the acoustics. Very large auditoria are difficult to fill with sound. Most of the direct sound will never reach the remoter parts, and the large surface area produces a corresponding absorption resulting in a weak level of reverberant sound. Little evidence for an ideal set of proportions exists for auditoria of conventional shape. Unconventional shapes introduce the risk of incorporating intolerable defects which prove impracticable to correct. Successful traditional concert halls are usually rectangular both in plan and section, e.g. Symphony Hall, Boston. This shape is convenient, and produces the reverberation time of up to two seconds preferred for symphonic music. With careful design, modern halls of non-rectangular shape can be extremely successful, a particular example being St David’s Hall, Cardiff. Where a shorter reverberation time is desired, other shapes are satisfactory, such as the horseshoe of the traditional opera house, and the fan for a theatre. The likelihood of audible echoes in large auditoria can usually be predicted, but conditions producing them are too various to summarise. Elimination of echoes is often expensive rather than technically difficult, an elegant example being the ‘flying saucers’ in the Royal Albert Hall, London. Auditoria for speech and drama have clarity as a prime requirement. The shape should ensure that the audience receives strong sound reflections immediately after the direct sound. For musical performances, many prefer early sound reflections arriving at the listener from a lateral direction. 3.02 Preferred dimensions – small rooms Small rooms can present serious acoustical problems, being often bedevilled with colouration, that is, the excessive accentuation of one or more notes of particular pitches. We particularly notice this phenomenon in bathrooms and telephone boxes, and it comes from the fact that the dimensions of these small rooms are comparable with the wavelengths of speech. The wavelength l in m of a tone of frequency f in Hz is given by l ¼ c/f where c is the velocity of sound (approximately 340 m/s in air). Colourations are particularly evident in rectangular rooms where the length, breadth and height bear a simple numerical ratio to each other; the theory for this is well understood. However, the ideal proportions have still to be discovered. 3.03 Acoustical models It has become quite usual to build a scale model of a proposed auditorium for acoustical testing. Any defects revealed by the tests can be dealt with before the full-scale auditorium is built. Models are particularly useful where an auditorium of novel shape is being considered. The scale factors range from 1:50 to 1:8. The 1:50 model gives less accurate results than models of larger scale, but this
Sound
disadvantage is generally outweighed by the lower costs of building, testing and modifying the smaller model. An alternative is to build a digital computer model of the proposed auditorium. A number of programmes are available which claim adequately to simulate the behaviour of sound in a mathematical model of the room. More recent digital simulation programmes claim to enable the designer to listen to sounds processed by the computer as though the listener were present in the completed hall.
4 NOISE 4.01 Noise criteria As the human ear is most sensitive to frequencies between 1 and 3 kHz, a 1 kHz tone will sound much louder than a 100 Hz tone of the same sound pressure level. Any measuring of loudness must take this frequency sensitivity into account, and the simplest of soundlevel meters has a device which roughly compensates for it called the A-weighting network. Readings from such a meter are designated A-weighted sound pressure levels (symbol LpA) to distinguish them from plain unweighted dB SPL (symbol Lp). Although the loudness and annoyance of a sound can depend on other factors than the A-weighted sound pressure level, it is a useful measure for many of the sounds encountered in and around buildings. A building performance specification may contain criteria expressed in A-weighted sound pressure levels for various areas, but where ventilation noise is likely to be significant, it is more usual for them to be given in Noise Criteria (NC) curves, or the similar Noise Rating (NR) curves, 41.2. These plot octave-band SPL against frequency. If NR-35 is specified, for example for a private office, then the noise level in any octave band should not exceed that indicated for the NR-35 line on the graph. The preference for the NC and NR criteria rather than the A-weighted SPL criterion arises from the octave-band data used in the design of mechanical services systems. Noise criteria are commonly specified as maxima rather than optimal levels, and this is a reflection of frequent failures to meet
41-3
the criteria many years ago. Unexpectedly, noisy systems are now much less likely and the consequences of systems, which are too, quiet are now often a matter of some concern. An office may be so quiet that private conversation can easily be overheard and occasional outside noises may be particularly distracting. In such a circumstance, a continuous masking (sometimes called white) noise may be deliberately introduced to help to drown other sounds, using loudspeakers or by increasing the ventilation system noise. Apart from A-weighted SPL, NC and NR ratings for noise, there are others the architect may encounter. Each has its merits, but most require rather more than a simple sound level meter for measurement. Some of these are: LA10,T
The A-weighted sound pressure level of a noise exceeded for 10% of a given time interval T
LA10,(18 h)
The average of the values of L10 measured hourly between 06.00 and 24.00 h on a normal working day. Used for planning and design as an index of road traffic noise
LAeq,T
The equivalent continuous A-weighted sound pressure level. This is the notional constant sound level which would give the same A-weighted sound energy as that of the actual varying sound over a specified period of time, T. This has become the preferred index for characterising a wide range of different kinds of sounds which are not steady. LAeq,T is used in a number of countries for rating industrial and transport noise.
LAr,T rating level
The measured equivalent continuous A-weighted sound pressure level plus any adjustment for the character of the noise. An adjustment would commonly be made for whines, hisses, screeches, hums, bangs, clicks, clatters or thumps.
All the above are measured in decibels. Considerable confusion may arise if the particular index is not identified in each case.
41.2 Noise rating curves
4.02 Internal noise sources Because effective noise insulation is often impractical and usually costly, noise-producing areas should be sited away from noise sensitive areas. In modern non-industrial buildings, the mechanical plant room is likely to be the noisiest area, especially if it contains heavy and inherently unbalanced plant. Chillers and large boilers can present severe noise problems particularly at low frequencies where curative measures are difficult. A buffer zone formed by a corridor or storage area around the plant room is a useful noise control measure. The airborne noise radiated by industrial machinery can usually be calculated sufficiently accurately using the manufacturer’s sound power level data. If the calculated noise level is too high, the reverberant noise level can be reduced by lining part of the plant room surfaces with an efficient acoustical absorbent; otherwise more costly measures may be necessary. The noise transmitted into the structure of the building via the machinery mounts, etc. is much more difficult to estimate. This is because the basic mechanical noise-generating characteristics of the machine are generally not known, and also because the ways in which sound propagates through building structures are imperfectly understood. In designing noise-isolation measures, rule-ofthumb methods are frequently used. They do not always work, and a long and expensive investigation is then needed to discover why; sound may easily propagate through structures with relatively little attenuation.
41-4
Sound
Many structure-borne noise problems are avoided by siting the plant room in a basement. When specifying ventilation noise levels, etc. the designer should take into account the noise arising from activities within the areas served, so that the criteria are compatible. In some circumstances, impact noise from footsteps can be a problem. As well as the effects on people within the building, due consideration must be given to the effects on the neighbourhood. Roof-mounted cooling towers may produce a noise problem in residential areas. Discotheques, nightclubs and other performance venues employing high-powered amplification systems are a potential noise nuisance. Planning conditions are often imposed on such developments and the planning authority may need convincing that adequate sound-insulation measures will be incorporated. 4.03 External noise sources The most important kind of external noise affecting buildings is transport noise from road traffic, aircraft and railways. An essential characteristic of such sources is that they are not generally under the control of those affected by their noise. It is therefore essential to assess the likely level of external noise to which a proposed building is to be subjected. If this is done early enough in the design process, the scheme can be economically produced to alleviate the effects of the noise. An example of planning against noise profoundly influencing the design is the five- to eight-storey Byker Wall in Newcastle upon-Tyne. Here, a barrier against the noise from an adjacent motorway is formed by a long block of flats. The flats all have small windows facing the motorway and the noise-sensitive rooms are on the quiet side of the barrier. The whole structure protects more conventional dwellings on the side remote from the traffic. Where the source of noise is known, it is often possible to calculate the likely noise level from its characteristics and the geometry of the site. In the UK, there is now an official procedure for calculating the noise from motor vehicles, and this is recommended as preferable to measurement. At first sight this seems strange, but in practice it can be difficult to achieve a valid measurement. Some cynics have suggested that in the British Isles the prevailing wind direction and speed and the rainfall are such that valid 18-h traffic noise measurements are impossible except on a few days in the year! Other sources of transport noise, such as railways, are not so well documented; direct site measurements may be the only course to take. In the case of the International Conference Centre in Birmingham with its concert hall and a railway line underneath, the main problem was structure-borne sound. A major part of the building was constructed on foundations incorporating vibration isolating elements. Aircraft are a well-publicised source of serious noise, and there are usually severe planning restrictions on dwellings close to airports. However, hotels are often built here, and with care in siting and design the noise problems can be successfully overcome. Public concern about jet engine noise has led to the development of quieter engines, and we can look forward to a diminution of the problem as the older aircraft are replaced. Other sources of noise that may have to be considered in particular situations include helicopters, hovercraft and industrial plant.
5 SOUND INSULATION When a sound wave strikes a wall, only a fraction of the incident sound energy is transmitted through the wall. The ratio of the incident to the transmitted sound energy, expressed in decibels, is called the sound reduction index. It can be properly measured only in a laboratory. The reduction in sound pressure level between adjacent rooms in an actual building depends not only on the sound reduction index of the separating wall, but also upon its
area, the acoustic absorption present in the receiving room and the amount of transmission by flanking paths (see 5.04). Neglecting flanking transmission, the relation between the average sound level difference between two rooms and the sound reduction index of the separating wall is Lp1 – Lp2 ¼ R þ 10 logðA=SÞ Where Lp1 ¼ sound pressure level averaged over the room containing the source Lp2 ¼ sound pressure level averaged over the receiving room R ¼ sound reduction index of the separating wall S ¼ area of separating wall in m2 A ¼ acoustic absorption of receiving room in m2 units. Often A is comparable in size to S, making the level difference Lp1 – Lp2 vary little from the sound reduction index R so that it is commonly referred to simply as the ‘sound insulation’.
5.01 Composite insulation 41.3 is an aid for calculating the sound insulation of a partition composed of two different materials. Consider a wall consisting of brickwork with insulation 45 dB and a glazed area amounting to one-fifth the total wall area of insulation 25 dB. On the vertical axis of 41.3, the area ratio 1:4 meets the 20 dB difference curve at 13 dB on the horizontal axis. The composite insulation is therefore 45 – 13 ¼ 32 dB.
5.02 Mass law To a first approximation the insulation of a single leaf wall or floor depends on its mass per unit area. From 41.4 the insulation
41.3 Variation in construction. An extreme example: a storeyheight crack 0.2 mm wide in a wall of 10 m2 could result in an insulation loss of 7 dB (From Guidance Note: Sound Insulation, HMSO, 1975)
Sound
41-5
41.4 Relationship of sound insulation to mass per unit area (from same as 41.3)
averaged over the frequency range 100–3150 Hz increases by about 5 dB for each doubling of mass (the mass law). 5.03 Coincidence effect The sound insulation also increases by 5–6 dB for each doubling of frequency provided the partition is very limp, for example a lead sheet. However, most partitions are fairly stiff. With some materials the stiffness combines with the mass in such a way as to produce a resonance effect, seriously reducing the insulation below the masslaw value. This resonance, called the coincidence effect, is caused by flexural waves in the partition, and its significance depends on its nature and thickness. For a 215 mm brick wall, the effect occurs at about 100 Hz, which is generally too low to matter. Window glass has coincidence frequencies in the upper audible range. 5.04 Flanking transmission In real buildings, sound is transmitted from one room to an adjacent room via many paths, 41.5. Where the separating wall has a sound reduction index of 35 dB or less, most of the sound is transmitted through the wall. If, however, we try to improve the insulation by using a heavier wall, the flanking paths, or indirect transmission routes, become more important. In fact, it is difficult to achieve better than 60 dB sound level difference without special measures, such as carefully designed structural discontinuities, to reduce the flanking transmission. 5.05 Openings Any kind of opening in a partition will seriously impair the sound insulation. The effect can be assessed by using 41.3, and assigning a value of 0 dB for the insulation of the opening. 5.06 Double walls Two single walls, each of 30 dB sound insulation, when combined would not produce 60 dB but only about 35 dB; the doubling of the mass per unit area adding 5 dB by the mass law. However, separating the two walls several metres apart would, if there were no flanking transmission, approach 60 dB. Practical double walls lie between these extremes, but it is difficult to theorise how a particular combination will actually behave. Double walls and multi-leaf partitions are used where the required mass of a single leaf would be excessive. They improve dramatically on the mass law at middle and high frequencies, but at low frequencies the insulation is usually little better, and sometimes worse than a single leaf of the same mass per unit area.
41.5 Sound transmission paths (from same as 41.3)
5.07 Floors The insulation of floors against airborne sound follows the same laws as for walls. An additional problem is the direct structural excitation of a hard-surfaced floor by footsteps, 41.5c. If a carpet is unacceptable, a floating floor must be used if footstep noise is to be reduced in the room underneath. The resilient element for such a floor may be of mineral wool, slab or blankets, rubber, expanded polystyrene or springs, but it is essential that the particular material that is chosen is known to be effective and durable. Care must be taken not to bridge this resilient element with any rigid connection to the base floor. The airborne sound insulation of a floor can be improved by suspending an impermeable ceiling below it, but the improvement is often limited by structural limitations on its weight and by height considerations.
5.08 Windows The windows are usually the weakest part of the envelope where sound insulation is concerned. The mass per unit area of the glazing is generally small compared with the rest of the envelope. Table II is a guide to the sound insulation of different windows. In order to obtain the highest insulation double glazing will be required, at least one pane of which is sealed. Specially, designed sound-attenuated ventilation will then be required.
5.09 Doors Single doors having a sound insulation greater than 35 dB are expensive and difficult to install. Seals are required around the edge to prevent leakages, and where these are effective they make the door hard to open and close. Magnetic door seals similar to those on refrigerators are a small improvement. The most effective solution where the space is available is the use of two moderately insulating doors separated by an absorbent-lined ‘sound lock’.
41-6
Sound
Table II Sound insulation of windows (from BRE Digest 140) Description
Any type of window when open
Sound reduction (av. 100–3150 Hz)
design, any more than a doctor would guarantee to cure a patient. The acoustical consultant’s task is to achieve the right balance between a design that is too costly initially and one for which failure would be disastrous.
About 10–15 dB
Ordinary single openable window closed but not weather-stripped, any glass
Up to 20 dB
Single fixed or openable weather-stripped window, with 6 mm glass
Up to 25 dB
Fixed single window with 12 mm glass
Up to 30 dB
Fixed single window with 24 mm glass
Up to 35 dB
Double window, openable but weather-stripped, 150–200 mm air space, any glass
Up to 40 dB
Double window in separate frames, one fixed, 300–400 mm air space, 6–10 mm glass, sound-absorbent reveals
Up to 45 dB
5.10 Barriers Barriers that intercept the line-of-sight between a sound source and the receiver are a common method of reducing a noise level. Outdoors, they are used as a shield against traffic and aircraft noise, and some types of machinery. Indoors, they are used in open-plan offices and schools, and for altering the acoustics of broadcasting and recording studios. The psychological effect of a visually opaque barrier can be very strong, giving a misleading impression of its acoustical effectiveness. For example, a line of trees is often proposed as a sound barrier although the measured acoustical effect is small. A bank of trees about 9 m in depth would be needed to provide an adequate acoustic screen for a motorway, for example. There have been extensive theoretical studies on the effectiveness of barriers in idealised situations, but not much has resulted which can be applied in practice. Quite apart from the nature and geometry of the barrier itself, its performance can depend appreciably on the frequency of the sound, the weather and the nature of the ground between source and receiver. As a rough guide, screen-type barriers 1–4 m high and mass about 10 kg/m2 can give transmission losses of 5–20 dB.
5.11 Enclosures Enclosures are used to suppress the noise from a stationary machine or item of plant such as a diesel generator. For them to be effective, they should have few or no openings. Where this is not possible because of the need to ventilate, properly designed attenuated air routes are required. The effectiveness of the enclosure is enhanced by lining internally with an acoustical absorbent. Telephone hoods are an example of a partial enclosure, the effectiveness of which depends on how well the user obstructs the opening.
5.12 Cost and the designer Structures designed to give a higher-than-average degree of sound insulation, such as broadcasting studios, are usually costly. The mass law, providing only a 5 dB increase for doubling the material used, illustrates how quickly the law of diminishing returns sets in. Attempts to beat the mass law by installing double or multi-leaf partitions incur the penalty of loss of usable space. It is usually difficult to increase the sound insulation of an existing modern building. Older buildings of heavy construction have been successfully converted into broadcasting and recording studios. Several local radio stations in the UK can bear witness to this. Because it is generally costly to increase sound insulation, the acoustical designer is rarely allowed the luxury of a safety margin. Unfortunately, the design of sound-insulating structures is still an imprecise science, and an economically designed building can fail to meet the expected performance. No reputable and knowledgeable acoustical consultant will guarantee the success of his or her
6 ACOUSTICAL TEST DATA Laboratory test data when required as proof of performance should be conducted in accordance with the relevant ISO standards and it is suggested that NAMAS or UKAS accredited data is a positive indication of a high level of accuracy regarding the repeatability and reproducibility of the test results. With regards to on site test data, it is now required in England and Wales and under the code for sustainable homes that testing be conducted by either a UKAS or ANC registered tested. For the rest of the UK, it is suggested that where on site performance testing is conducted the tester be a registered member of the Institute of Acoustics.
7 STANDARDS AND CODES OF PRACTICE There are a growing number of national, European and international standards and codes of practice, some of which are listed in the Bibliography at the end of this chapter. These are invaluable in defining the methods used in testing acoustical materials, measuring environmental noise, traffic noise, etc. These advances enable a more objective assessment to be made of an acoustical material, device or situation.
8 LEGISLATION The architect has now to take into account a growing body of legislation concerned with reducing the objectionable effects of noise generated within his or her building, and the effects of external noise sources on the occupants. The Building Regulations lay down the requirements for sound transmission of walls, floors and stairs in dwellings. In addition, in England and Wales, the legislation also includes control of reverberation times in common areas as well as sound insulation and control of the acoustic environment within schools (detailed in Building Bulletin 93) and habitable areas (i.e. university halls). In dwellings, the general requirement is that the relevant element shall resist the transmission of airborne/impact sound. Useful guidance on methods to achieve the requirements is given in Approved Document E (for England and Wales), Technical Booklet G/G1 (for Northern Ireland) or Section 5 (for Scotland). In addition, compliance with the legislative guidance in England and Wales can be achieved by constructing in accordance with the details issued under the Robust Details. Designers should be aware that completion in England and Wales is demonstrated by either undertaking a minimum of 10% on site testing or by registration with a compliance scheme (Robust Details). A higher percentage of acoustic testing would also be required should the designer wish to gain points under the Code for Sustainable Homes. Current regulations apply to conversions as well as to new constructions with differing requirements for each being applied in England and Wales. See Table III. In other countries, other forms of legislative control apply. In the USA, the Environmental Protection Agency demands that a proposed development is preceded by an Environmental Impact Statement to show that no noise nuisance will result from it. European countries have specific noise limits for sanitary facilities such as WCs. Many countries have strict planning controls near known noise sources such as airports, and some provide financial assistance to insulate against sound in the proximity of motorways, etc.
Sound
41-7
Table III Sound insulation values for testing Regulations
Walls
Floors
Mean value
Individual value
Mean value
Individual value
DnT,w þCtr
N/A
DnT,w þCtr
N/A
England and Wales ADE Dwelling-houses and flats – Purpose Built
45 dB
45 dB L9nT,w 62 dB
Dwelling-houses and flats – Purpose Built
DnT,w þCtr
N/A
43 dB
DnT,w þCtr
N/A
45 dB L9nT,w 64 dB
Scotland Section 5 Dwelling Houses – purpose built and conversion
DnT,w
DnT,w
DnT,w
DnT,w
53 dB
49 dB
52 dB
48 dB
L9nT,w
L9nT,w
61 dB
65 dB
Northern Ireland TB G /G1 Dwelling Houses – purpose built and conversion
Dwelling Houses – conversion
DnT,w
DnT,w
DnT,w
DnT,w
53 dB
49 dB
52 dB
48 dB
N/A
DnT,w 49 dB
L9nT,w
L9nT,w
61 dB
65 dB
N/A
DnT,w 48 dB L9nT,w 65 dB
Note: At the time of publication, the Scottish regulations were under review
9 BIBLIOGRAPHY BS 5228 Code of Practice for noise control on construction and open sites BS 8233 Code of Practice for sound insulation and noise reduction for buildings ISO EN BS 140 Acoustics – Measurement of sound insulation in buildings and of building elements ISO EN BS 717 Methods for rating the sound insulation in buildings and of building elements BS 3638 Method for measurement of sound absorption in a reverberation room BS 6864 Laboratory tests on noise emission from appliances and equipment intended for use in water supply installations BS 4142 Method for rating industrial noise affecting mixed residential and industrial areas ISO 6242–3 Building construction – Expression of user’s requirements – Part 3: Acoustical requirements ISO 1996 Acoustics – Description and measurement of environmental noise Part 1 Basic quantities and procedures Part 2 Acquisition of data pertinent to land use
Part 3 Application to noise limits Department of the Environment and the Welsh Office, The Building Regulations 2003 – Approved Document E Resistance to the passage of sound, HMSO, London Building Standards (Scotland) Regulations Section 5, 1990, as amended, HMSO, London DOE Northern Ireland Technical Booklet G/G1 1990, HMSO, London Department of the Environment, Calculation of road traffic noise, London, 1988 Noise Insulation Regulations 1975, HMSO, London Department of Transport, Railway noise and the insulation of dwellings, HMSO, London, 1991 Department of the Environment, Planning Policy Guidance – PPG24, HMSO, London, 1994 Department of the Environment, Digests, Information Papers, Building Research Establishment, Garston, Watford, WD2 7JR Robust Standards Details, Robust Details Ltd Housing and Sound Insulation Improving existing attached dwellings and designing for conversions SBSA, Historic Scotland, Communities Scotland