Environmental Science By Tim South – licensed under the Creative Commons Attribution – Non-Commercial – Share Alike License

Why it matters Tim South Leeds Metropolitan University

What are the acoustic issues in a completed building? Sound insulation –Between dwellings –Between rooms in a building Reverberation in rooms Internal noise levels –From building services –From outside Noise emitted from the building

Any extra issues during construction? Noise exposure of the workforce Hand-arm vibration Construction noise Vibration eg from piling

Objectives By the end of this lecture you should be able to: Understand the properties of sound. Identify the various noise problems that arise in buildings. Understand how reflection, absorption and reverberation affect room acoustics. Understand how good sound insulation can be achieved. Be aware of the requirements of Building Regulations Part E.

What is sound? A disturbance in the atmosphere Travels in three dimensions Pressure fluctuations are small Sound is measured in pascals (Pa); 1 pascal is equivalent to 1 newton per square metre Normal atmospheric pressure is about 100,000 Pa A noisy environment may involve a sound pressure of about 1 Pa

What is sound? Sound pressure is the deviation from atmospheric pressure due to the passage of a sound wave A 1% fluctuation is caused by a very loud sound indeed. For comparison, normal weather variations may cause a pressure change of 3,000Pa or 3% in the course of a day Noise is the same as sound It is normally called noise if it is unwanted

Sound waves Are longitudinal waves ie the chunks of air move backwards and forwards in the direction the wave travels This is very difficult to draw So in practice they are often represented as graphs of pressure against either time or distance

Frequency and wavelength The frequency of a wave is the number of waves arriving at a fixed point in one second Normal symbol f The unit of frequency is the hertz (formerly the cycle per second) The wavelength is the length of one complete cycle of the wave Normal symbol Normal symbol The unit of wavelength is the metre

Frequency The human ear can hear sound with frequencies from 20 Hz to 20,000 Hz We are most sensitive to the middle range, particularly 1-3 kHz These frequencies are also the most damaging A system called A weighting is used for many measurements to approximate human hearing

If you multiply the frequency of any wave by the wavelength, you get its velocity The velocity of sound in air varies with temperature At “normal” temperatures it is about 340 ms -1 So frequency can easily be converted to wavelength and vice versa Audible wavelengths are from a few metres to a few millimetres Velocity, frequency and wavelength

Wave properties Sound waves demonstrate the following properties, which are common to all waves; RefractionDiffractionReflectionInterference

Refraction Waves bend when passing from one medium to another They bend towards the normal if their velocity is greater in the second medium Water looks shallower than it is Air - higher speed Water - lower speed Observer Normal Actual depth Apparent depth

Refraction of sound waves The velocity of sound is different in layers of air at different temperatures Normally air temperature decreases with height, and sound waves bend away from the ground A temperature inversion causes them to bend towards the ground. Sound is the audible at much greater distances.

Diffraction The tendency of waves to bend round corners More pronounced at long wavelengths Not always obvious with light (but try squinting at a sodium street light) Sound waves have longer wavelengths and readily bend round corners So you can hear a fire alarm in the corridor Or someone talking about you in the next room Limits the effect of roadside noise barriers

Reflection Familiar in the case of light waves Surfaces may reflect in various ways; –Partial –Total –Specular –Diffuse Focusing by a concave mirror

Reflection of sound waves Noise levels increased if there is a hard surface behind the source A large building can make an aircraft appear to be in the opposite direction Sound levels in rooms a result of multiple reflections from surfaces Concave surfaces can focus sound Surfaces may reflect different frequencies to different extents

Interference Two sound waves can combine to set up a pattern of standing waves Particularly at low frequencies This is the principle on which some musical instruments work It can cause problems in rooms

The decibel scale? “Everyone” knows we measure sound levels in decibels Few people know much more about the scale It is based on logarithms, so calculations can be complicated The reasons for using this scale are not very clear But everyone else uses it, and… …you get nice numbers (0-100 ±½)

Sound pressure level L p is the sound pressure level Measured in decibels Some other quantities are measured in decibels too L p is still sometimes called SPL

Addition of decibels The decibel scale makes addition a bit complicated Suppose we measure the sound pressure level at a point with one source operating – L 1 Then we switch off the first source, switch on a different one and measure the sound pressure level at the same reception point – L 2 What sound pressure level L p would be measured at that point if both sources operated?

Graphical addition

Graphical addition - example Two noise sources individually cause L p s of 86 and 88 dB at a point. What L p will result from both sources simultaneously? = 2dB Add 2 dB to the higher level; 88 = 2 = 90 dB

Simple addition of decibels We have a noise source operating and the meter reads 80 dB If we add an identical noise source at the same position, the meter reading will go up to 83 dB In general, –Doubling the noise sources adds 3 dB to L p –Halving the sources reduces L p by 3 dB

Sound power level The sound power level (L W ) is a measure of the noise emitted by a source Not the same as sound pressure level Often labelled on outdoor equipment Can be used to make L p predictions

Point sources Small compared with their distance In the free field, sound levels fall by 6 dB every time you double the distance

Line sources Extended in one dimension In the free field, sound levels fall by 3 dB every time you double the distance

Prediction of sound levels Radiated from a point source outdoors Indoors, there are multiple reflections from surfaces and predictions are more complicated L p = L W - 20  logr -11 L p = L W -10  logr - 8

Acoustics in buildings Sound insulation - between rooms Sound absorption - within a room The two ideas are often confused by non- specialists Particularly in complex structures (eg partition walls), the absorption and insulation work together to control noise

Sound absorption Panel materials (absorb at low frequencies) –eg plasterboard walls Porous materials (absorb at high frequencies) –Stability of porous surfaces is a problem Traditionally absorption comes mainly from suspended ceilings Combination absorbers can be “tuned” to requirements across the frequency range

Reverberation Reverberation time (RT) is a measure of how long it takes sound to die away It is the simplest measure of acoustic conditions inside a room Sound absorbing surfaces tend to reduce the RT Reflective surfaces tend to increase it

Reverberation times Rooms for speech should have an RT less than 1s (<0.8s required for school classrooms) For music the RT should be longer (depends on the type of music) Long RTs reduce speech intelligibility Very short RTs stop sound propagating around the room

Reverberation times Rooms for speech should have an RT less than 1s (<0.8s required for school classrooms) For music the RT should be longer (depends on the type) Long RTs reduce speech intelligibility Very short RTs stop sound propagation around the room

Reverberation times Rooms for speech should have an RT less than 1s (<0.8s required for school classrooms) For music the RT should be longer (depends on the type) Long RTs reduce speech intelligibility Very short RTs stop sound propagation around the room

Sound insulation Traditionally insulation was achieved by high surface mass and high integrity There is a move from masonry walls towards lightweight structures Combining sound insulation and sound absorption principles means lightweight structures can perform better than masonry structures

Sound insulation Laboratory measurements Field measurements

Two common quantities R w Weighted sound reduction index Measured in a laboratory Relates to a particular material or product D nT,w Weighted, standardised level difference Measured in a real building Used to specify building performance

The difference between R w and D nT,w depends on Room shape and size Weak spots where two building elements join Workmanship issues Flanking transmission

Sound insulation Often the sound insulation is decided by the weak component in a partition. This may be; –There by design (eg a door) –Due to faulty design or workmanship (eg a continuous cavity above a suspended ceiling) –Difficult to avoid (eg ventilation ducts)

Air leakage paths – an illustration

Building Regs Good walls Improved Original Sound insulation in decibels Air leakage paths

Flanking transmission Direct sound

Flanking transmission Flanking paths become important once the direct sound has been reduced May need to introduce structure breaks etc A continuous floor slab (as shown) would not be allowed for party walls Direct sound

Improving sound insulation Increasing sound insulation performance Increase mass Reduce flanking Eliminate gaps

Sound insulation - door considerations A door plus frame will typically be rated at about 28 dB of sound insulation If it takes up 10% of the surface area, then however good the wall system the maximum sound insulation is 38 dB. This assumes perfect installation Doors should never be installed between occupied rooms

Sound insulation is dead simple L´ nT,w D nT RwRw D nT,w DwDw R´ w C tr D n,e D nT,w + C tr D 2m,n R tr,s - not

Part E The Building Act The Building Regulations 2000, as amended in 2002 Approved Document E edition The law applying in Scotland is different

Purpose “…securing reasonable standards of health and safety …(and welfare and convenience) …for persons in and about the building.” (Other regulations include energy conservation and prevention of water contamination in their purposes)

Regulation E1 (2002 version) Dwelling-houses, flats and rooms for residential purposes shall be designed and constructed in such a way that they provide reasonable resistance to sound from other parts of the same building and from adjoining buildings.

Regulation E2 (2002 version) Dwelling-houses, flats and rooms for residential purposes shall be designed and constructed in such a way that (a) internal walls between a bedroom or a room containing a water closet, and other rooms, and (b) Internal floors, Provide reasonable resistance to sound.

Regulation E3 (2002 version) The common internal parts of buildings which contain flats or rooms for residential purposes shall be designed and constructed in such a way as to prevent more reverberation around the common parts than is reasonable

Regulation E4 (2002 version) (1) Each room or space in a school building shall be designed and constructed in such a way that it has the acoustic conditions, and the insulation against disturbance by noise appropriate to its intended use. (2) For the purpose of this part – “school” – has then same meaning as in section 4 of the Education act 1996, and “school building” means any building forming a school or part of a school.

Buildings and structures covered Residential buildings Schools Party walls (airborne sound) Party floors and stairs (airborne and impact sound) Some internal walls Common areas Hospitals, offices, prisons Most internal walls within a dwelling External walls Buildings and structures not covered

Ways of complying with the Regulation – converted buildings Test 10% of party walls and floor as they are completed Internal walls and reverberation in common areas are approved on the basis of the plans submitted (no testing)

Ways of complying with the Regulation – New buildings Test 10% of party walls and floor as they are completed Or Use Robust Details Internal walls and reverberation in common areas are approved on the basis of the plans submitted (no testing)

Ways of complying with the Regulation – School buildings Submit plans to the building inspector showing how the requirements are to be met. They are approved on the basis of the plans submitted (no testing)

Standards for sound insulation – new buildings Airborne D nT,w + C tr ≥ 45 dB for walls and floors in flats and houses Airborne D nT,w + C tr ≥ 45 dB for floors in rooms for residential purposes Airborne D nT,w + C tr ≥ 43 dB for walls in rooms for residential purposes Impact L nT,w ≤ 62 dB in flats, houses and rooms for residential purposes

Standards for sound insulation – converted buildings Airborne D nT,w + C tr ≥ 43 dB for walls and floors in flats and houses Airborne D nT,w + C tr ≥ 43 dB for floors in rooms for residential purposes Airborne D nT,w + C tr ≥ 43 dB for walls in rooms for residential purposes Impact L nT,w ≤ 64 dB in flats, houses and rooms for residential purposes

Standards for sound insulation – internal walls and floors R w ≥ 40 dB in each case

Reverberation standards Cover an area equal to the floor area with an absorbing material meeting absorption class D or better Or 50% of the floor area with an absorber meeting absorption class C or better Or Make sure that from 250 Hz to 4 kHz the absorption area is at least 0.2 m 2 per cubic metre (for entrances) or at least 0.25 m 2 per cubic metre (for corridors or hallways)

Conversions In the case of a historic building it may not be practical to meet the required standards within the requirements of the listed Building Regulations In this case it may be agreed that the sound insulation performance is measured and is then declared via a notice fixed to the building in a conspicuous place.

BB93 requirements for school buildings - sound insulation between rooms Rooms are divided (table 1.1) into categories according to –how much noise they generate –How sensitive they are to noise Sound insulation is specified as D nT,w A value of D nT,w is specified for each pair of rooms - table 1.2

BB93 D nT,w requirements Classroom - classroom 45 dB Music room – music room 55 dB Hall – drama studio 55 dB Between open-plan teaching areas 40 dB

Sound insulation between rooms and circulation areas Very difficult to measure, so this is specified in terms of R w (ie manufacturer’s data) Two specifications - music rooms and everywhere else Normally determined by the size and specification of the door

Robust Details The Robust Details are contained in a manual published by Robust Details Ltd Plot must be registered with Robust Details in advance RD inspectors can check on the work Sample testing to monitor each RD No completion testing on each development

Robust details exist for Walls –Masonry –Steel –Timber Floors –Concrete –Timber –Steel-concrete composite

Robust Details Detailed requirements Particularly for junctions Use generic materials –In theory Specifications include density etc Checklists

Example – masonry walls Separating walls - masonry E-WM-1 Masonry - dense aggregate blockwork (wet plaster) E-WM-2 E-WM-2 Masonry - lightweight aggregate blockwork (wet plaster) E-WM-3 Masonry - dense aggregate blockwork (render and gypsum-based board) E-WM-4 Masonry - lightweight aggregate blockwork (render and gypsum-based board) E-WM-5 Masonry - Besblock "Star Performer" cellular blockwork (render and gypsum-based board) E-WM-6 Masonry - aircrete blockwork (render and gypsum-based board) E-WM-7 Not Currently Available E-WM-8 Masonry - lightweight aggregate blockwork British-Gypsum-Isover ISOWOOL (gypsum-based board)

Robust Details problems Checklists Some bad failures Detailing – recent advice on mortar in cavity walls

Problems with the Building Regulations Was the move from D nT,w to frequency noise) D nT,w + C tr justified? Is Regulation E too limited in scope? Do they discourage the development of new materials and techniques which provide higher levels of sound insulation? Do Building Inspectors have the necessary specialist expertise?

Further information Approved Document E. HMSO, 2003 Resistance to the Passage of Sound BR_PDF_ADE_2003.pdf DfES (2003). BB93; Acoustic Design of Schools TSO Smith, Peters and Owen (1996) Acoustics and Noise Control 2 nd Edition. Longman