Sound Insulation and Noise Reduction for Office Building

Environmental noise

Guidelines: For steady external noise source (such as road traffic) the internal ambient noise should not exceed the values in table 1:

Table 1: Indoor ambient noise levels for dwellings (British Standard Institution, 2014)

To avoid sleep disturbance, the WHO’s guideline values for bedrooms are: 30 dB L_Aeq for continuous noise and 45 dB L_{Amax ,F}  for single sound events. With windows open, the sound pressure level on the outside façade of the bedroom should not exceed 45 dB L_Aeq and 60 dB L_{Amax, F}. With windows closed (a 30 dB reduction in sound pressure level), the desirable external noise levels should not exceed the values in table 2:

Table 2: External noise levels dwellings with windows closed (British Standard Institution, 2014)

For the gardens and patios, the goal is not to exceed the 50dB L_Aeq in external noise level. In noisier environments, an upper limit of 55dB L_Aeq can be acceptable too. In areas where development activities are taking place, it might not be possible to achieve these values (British Standard Institution, 2014).

Potential negative effects: The noise can cause many health and wellbeing issues. Specific negative effects can be outlined as: communication disturbance, hearing loss, sleep disturbance, cardiovascular and psychological issues, and performance reduction and even damage the person’s social behaviour. In dwellings, sleep disturbance, annoyance and speech interference are the main negative effects (Berglund et al., 1999).

Other aspects of design: Ventilation is necessary for provision of fresh air, removal of pollutants, humidity control and helping to meet the thermal comfort needs (Building Regulations, 2010). Opening windows can have qualitative benefits such as individual control of the environment, feeling connected to the outdoors and perception of the fresh air but if a non-acoustically-attenuated window is the only means for avoiding overheating and/or pollutant accumulation and the building is located in a noisy area, the occupant has to choose between an annoying high level of noise or annoying high temperatures (Chilton et al., 2016). (In practice dwellings are designed to achieve the internal guidelines with windows closed). Where possible, trickle ventilators should be kept open (British Standard Institution, 2014). In case of using some of the lighting fixtures e.g. fluorescent tubes, there might be an audible and buzzing noise.

Mitigation strategies: Site planning, orientation and barrier block: maximising the distance between the noise source and the noise-sensitive parts of the building and also providing soft ground cover.

Sound insulation: The sound insulation of roof and façade. Regarding the “sound reduction index”, of the facades, heavier construction materials tend to result in a higher level of sound reduction but this function will be greatly affected by the less effective elements such as windows and trickle vents (Berglund et al., 1999).

Screening: using purpose-built screens or natural features such as earth banks to block the direct path from the source to the receiver can disturb the propagation of sound. Screens can show a better effectivity at higher frequencies and when placed close to either the sound source or the receiver. In practice it is not easy to achieve a decrease in sound pressure level greater than 10 dB (Berglund et al., 1999). The application of green space can also help ease the effects which will be mostly related to psychoacoustics.

Sound insulation of the building envelope and office design

Traffic noise levels on the façade: With traffic noise being 68 ± 2 dB L_Aeq,16h at 30 m from the centre of the road and the office building being at 90 m distance from the centreline of the road:

L₂-L₁=10Log r₁/r₂= 10 Log (30/90) = -4.7 dB

L₂= 68-4.7=63.3 ± 2 dB                 road traffic noise level incident on the façade

The resulting noise levels with regards to ventilation methods are shown in table 3:

Table 3: Noise levels in different ventilation methods

The client avoids a full mechanical system and relying on natural ventilation will result in noise levels higher than 40 dB, therefore using a hybrid system which partially relies on mechanical systems and attenuated passive ventilation openings is suggested to meet the requirements.

Background sound: Noise and speech privacy are two important factors in office acoustic environment (Jensen, Arens and Zagreus, 2005). Ambient silence can be as distracting as a loud environment as it highlights acoustic disturbance and decreases speech privacy, therefore the ambient background noise level can be useful as it can help mask the speech from an adjacent space and improve confidentiality. Overhearing private conversations in the offices has been named as one of the main causes of acoustic dissatisfaction in open-plan offices where a moderate noise level can help in providing masking for acoustic privacy. Sound masking systems supply a low level of background noise to provide a level of confidentiality for the workers in their communications and can decrease the distraction caused by aural interruptions (International well building institute, 2017). In practice, the required background noise is generated through mechanical ventilation systems or by installing a speech masking system. The privacy improves as the continuous background noise level is increased, but with a higher background noise level, there would be an increase in the chance of employees being disturbed. Selecting an appropriate background noise level requires a balance between these conflicting ideas.

Guidance from standards: recommendations andguidelinesfrom different standards can be found in tables 4-8

Table 4: BCO 2014 guides for indoor ambient noise levels in offices-Noise rating limits (class notes)

Table 5: BS 8233:2014 guides for indoor ambient noise levels in offices-L_Aeq,T limits

Table 6: BREEAM acoustic performance guides (Hea 05 Acoustic performance, 2016)

Table 7: WELL Building Standard credits for acoustic performance (International WELL Building Institute, 2016)

Table 8: LEED credits for acoustic performance (Acoustic Performance, 2018)

Design recommendations:

• For general open-plan offices, floor to ceiling height should not exceed 3 meters and should have high sound absorption
• Covering the floors with carpet in the office and adjacent circulation areas is recommended (BCO, 2009)
• Screening should be absorbent-faced and at least 1.5 m high.
• If the ceilings are higher than 3 m, it is difficult to provide acceptable acoustic environment with absorption coverage lower than Class A.
• Large office equipment that makes too much noise should be kept in a well-screened area or a separate room (British Standards Institution, 2014)

Two acoustic products: Sound reduction treatments that include absorptive surfaces such as wall panels, ceiling baffles and surface enhancements can help with reverberation management and improve acoustic comfort (WELL Building Standard, 2017). Class A ceiling tiles covering all areas except for lights and grills are recommended. Carpet is desirable in offices to control impact noises such as footfall and provides additional absorption. Hard floor finishes should be avoided in offices.

Internal sound insulation design

The airborne sound insulation of the wall is controlled by the overall mass (Gov.uk, 2010).

R_w= D_nT,w + 10 log S/A   dB

Where

S= surface area of the wall= 5*2.4=12 m²

A= total or equivalent absorption surface, receiver room= 0.16 V/T= 0.16*36/0.5= 11.52 m²

V= receiving room volume= 5*3*2.4=36 m³

T= reverberation time= 0.5 sec

Table 9: calculation of on-site sound insulation performance

The real world conditions should be applied to calculated numbers and the real numbers can be 5-10 dB worse than predicted. With regards to requirement of on-site sound insulation performance of ≥45, type 4 is recommended. Type 3 can be the second option.

The resistance to airborne sound in both types depends on the mass per unit area of the leaves, mechanical isolation (the isolation of the frames or the studs) and the acoustic isolation through the cavity and the insulation (Building Regulations, 2003, British Gypsum White book, 2015). It is important that the mechanical isolation is maintained and services, fixtures etc. do not form a bridge between the two linings.

In general, for achieving the optimum acoustic performance, the junctions between the separating walls and other elements such as the roof, floor and external walls should be carefully detailed. It is recommended that the wall is continuous to the underside of the roof. The junction between the separating wall and the roof should be filled with a flexible closer (Building Regulations, 2003).

Room acoustics-reverberation time

Reverberation time is the time required for the level of a steady sound to decay by 60 dB after the sound has stopped, table 10-11.

Table 10: reverberation time and upper limits for indoor ambient noise levels (Department for Education, 2015)

Table 11: performance standard for reverberation time based on the floor area (Department for Education, 2015)

Calculating the reverberation time for the swimming pool:

T=0.16V/A

A=α * S  A=α₁ * S₁+ α₂ * S₂+ α₃ * S₃+…

Where

T= reverberation time in seconds

V= room volume=65*35*3.8=8645 m³

A= total or equivalent absorption surface in m²

α= absorption coefficient

S= absorbing surface area in m²

Standard profiled deck:

A=0.1*(3.8*65)*2+0.1*(35*3.8)*2+ 0.01*(35*65) +0.1*(35*65) = 326.25

T= 0.16 * 8645/326.25= 4.24 sec

Acoustic profiled deck:

A=0.1*(3.8*65)*2+0.1*(35*3.8)*2+ 0.01*(35*65) +0.8*(35*65) = 1918.75

T=0.16 * 8645/1918.75= 0.72 sec

Based on the results, the acoustic profiled deck provides a better acoustic environment.

Commentary: BB93 specifies the upper limit for indoor ambient noise level in the swimming pool as 50 L_Aeq,30mins dB. Swimming pools usually have long reverberation times due to the nature of their construction and surface materials. This can result in high noise levels and poor speech intelligibility (IOA and ANC, 2015). This undesirable acoustic environment will expose the users and staff to exhausting situations, especially the staff who have to spend longer hours in the area-employees should not be exposed to an equivalent SPL of 85 dB L_eq,8h for daily activities. Apart from being exposed to high SPL, they might need to struggle for having normal conversations as the speech intelligibility is usually affected. A poor speech intelligibility will result in unclear and disturbed communications between the staff, users or the tutor and the learners (Department for Education, 2015). In order to overcome this situation, people tend to raise their voice which can add to the acoustic disturbance of the environment and also can cause physiological and mental issues in the users and especially the staff (Hall, 2016). Improving the acoustic situation through using absorbent surfaces, decreasing the ceiling height and avoiding parallel hard surfaces and therefore decreasing the reverberation time can stop these adverse effects on the staff and the users (IOA and ANC, 2015; Hall, 2016).

Sound insulation and privacy

Effects on wellbeing: There are four different features of sound in a hospital:

• Noise
• Speech privacy
• Speech intelligibility
• Music

Hospitals are extremely noisy and the noise levels usually exceed the recommended guidelines by far. A poor acoustic environment has adverse effects on patients’ privacy if there is a chance that their private consultations with staff or the conversations between staff members can be overheard (Joseph and Ulrich, 2007). A study in an emergency department shows 5% of the patients examined in the curtained area reported refraining from mentioning their private health history and even refusing parts of the physical examination due to a sense of lack of privacy. This issue can have serious adverse effect on patient’s safety (Barlas et al. 2001 as mentioned in Joseph and Ulrich, 2007). Lack of confidentiality happens due to a lack of enough spaces for private discussions in public areas, close proximity of staff and people at reception, curtain-enclosed areas instead of wall-enclosed areas and continuous sound reflection due to non-absorbing ceilings. Also, it might affect the operation and wellbeing of staff as they fear there might be some important issues that they are not aware of which can threathen the health and safety of the patient. On the other hand some regulations suggest that there is a conflict in the issue of privacy in the hospitals: the need for the medical staff to hear the sounds of distress and to have rapid access to the patients is likely to be more important than the patient’s need for privacy (Department for communities and local government, 2016).

Students with special hearing or communication needs: It has been stated that the majority of health professionals lack the necessary communication skills to communicate with their patients with hearing impairment (BID-Services, 2016). The range of special hearing or communication needs in students include:

• Speech, language and communication difficulties
• Visual impairments
• Fluctuating hearing impairments caused by conductive hearing loss
• Attention deficit hyperactivity disorder (ADHD)
• Auditory processing disorder
• Being on the autistic spectrum (Department for Education, 2015, p:13)

It is recommended to have an integrated system for wayfinding, public address and hearing enhancement. A person with hearing impairment needs to receive a signal that is amplified in both volume and signal to noise ratio in order to be able engage in a conversation with their physician. The methods currently available to provide this situation are induction loop (with the risk of signal overlap in adjacent spaces), infrared and radio. Also the presence of any of these hearing enhancement systems should be displayed through standard symbols (Gov.uk, 2015).

Noise and reverberation can affect people with hearing impairment more seriously (Shield and Dockrell, 2003). Also people, who are blind or partially sighted, relying on the quality and character of the reflected sound, might find it confusing because of the longer reverberation time. People with sensory difficulties might experience a state of sensory overload in a highly reverberant environment (British Standard Institution, 2018).

Many people with hearing or communication impairment will rely on lip reading or note taking as a means to communicate; therefore it is essential to have the suitable level of (artificial) lighting so that they can see the face of the person they are speaking to.

Privacy standards and elements of acoustic design: there are 3 elements to the sound insulation of a hospital room: privacy requirement, noise generation of the source room and noise sensitivity of the receiving room, table 12

• “Confidential: raised speech would be audible but not intelligible and normal speech would be inaudible e.g. consulting room, examination room
• Private: normal speech would be audible but not intelligible e.g. operating theatres
• Moderate: normal speech would be audible and intelligible but not intrusive e.g. multi-bed rooms, nurseries
• Not private: normal speech would be clearly audible and intelligible e.g. dirty/clean utilities, waiting area
• Sensitive: room cannot accommodate any noticeable noise from rooms next door e.g. speech and language therapy
• Medium sensitivity: room generally needs to be free from noise of other rooms e.g. consulting room
• Not sensitive: noise from other rooms does not affect the use of the receiving room e.g. corridors” (Department of Health, 2013, p:9)

Table 12: sound insulation ratings to be achieved on site ((Department of Health, 2013).

Room acoustics-performance space

Multipurpose halls are used for a variety of applications which result in more acoustic complexities as different applications (lecture and speech versus music and concerts) sometimes have conflicting requirements, table 13.

Table 13: the conflicting requirements of speech and music (IOA and ANC, 2015, p:48)

Indoor ambient noise level: in the lecture hall the ambient noise level is very important as the lecturer’s voice should be clearly heard above the background noise. The background noise can be produced as a result of several factors including noise from external sources and building services. BB93 specifies the upper limit for indoor ambient noise level for both the lecture and the performance/recital room as 35 L_Aeq,30mins dB. In the performance room, the selection of quiet fans and using attenuators for mechanical ventilation is important (Department for Education, 2015; IOA and ANC, 2015).

Room size, geometry and reverberation time: The floor area, height, room shape and volume will affect the reverberation time. Long reverberation time is usually preferable for music and performance halls while it can decrease sound intelligibility for the lecture and the speech. BB93 specifies the reverberation time for lecture rooms with more than 50 people as ≤1 second and for the performance/recital as 1.0-1.5 second. Geometry of a performance room determines the sequence of sound reflections from different surfaces to the listener (Department for Education, 2015; IOA and ANC, 2015).

The acoustic absorption and distribution of the absorbents: Usually it is recommended to have the acoustic absorbent materials reasonably evenly distributed in the room. Occupants act as absorbents therefore in the performance room (with large numbers of occupants) the absorbent material are usually located on higher levels of walls. Acoustically absorbent seats with upholstered backs are common to use in a music hall. In music rooms or auditoriums surfaces around or above the stage are usually reflective to provide feedback for the performers (IOA and ANC, 2015).

Diffusion of the sound: the diffusive properties of the surfaces should be considered as they can affect the sound absorption and avoid problems such as standing waves and flutter echoes (IOA and ANC, 2015).

References

Acoustic Performance (2018) Available at https://www.usgbc.org/credits/eq10?view=language (Accessed 24 March 2018)

Berglund, B. et al. (1999) ‘Guidelines for community noise’. doi: 10.1016/S0065-2776(08)60014-0. Available at: http://www.who.int/iris/handle/10665/66217 (Accessed 29 March 2018)

BID-Services (2016) ‘A guide to working with deaf people in a health setting’, 2016(20.11.2016). Available at: http://www.bid.org.uk/downloads/resources/a5-guide-to-working-with-deaf-people-in-a-health-setting.pdf. (Accessed 29 March 2018)

British Gypsum White Book, (2015) C04.S06.P02-P12:GypWall staggered. Available at http://www.british-gypsum.com/~/media/Files/British-Gypsum/White-Book/White-Book-C04-S06-Partitions-GypWall-STAGGERED.pdf?la=en (Accessed 26 March 2018)

British Standard Institution, (2014) BS8233: Guidance on sound insulation and noise reduction for buildings. Available through UCL database

British Council for Offices (2014) ‘Guide to Specification’ (based on the lecture notes)

Building Regulations (2003) ‘Approved Document E: Resistance to the passage of sound’. Available at https://www.gov.uk/government/publications/resistance-to-sound-approved-document-e (Accessed 29 March 2018).

Building Regulations (2010) ‘Approved Document F: Ventilation’. Available at https://www.gov.uk/government/publications/ventilation-approved-document-f (Accessed 29 March 2018).

Building Regulations (2015) ‘Approved Document M: Access to and use of buildings, volume 2-buildings other than dwellings’. Available at https://www.gov.uk/government/publications/access-to-and-use-of-buildings-approved-document-m (Accessed 29 March 2018).

Chilton, A. et al. (2016) ‘Ventilation and Residential Developments Overheating’, Institute of Acoustics, 38, pp. 48–56.

Department for Communites and Local Government (2016) Approved Document E Frequently Asked Questions. Available at https://www.gov.uk/government/publications/resistance-to-sound-approved-document-e (Accessed 29 March 2018)

Department for Education (2015) Acoustic design of schools: performance standards, Building bulletin 93. Available at: https://www.gov.uk/government/publications/bb93-acoustic-design-of-schools-performance-standards.

Department of Health (2013) ‘Specialist services Health Technical Memorandum 08-01: Acoustics’, p. 48. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/144248/HTM_08-01.pdf.

Hall, M. (2016) ‘Acoustic Design of Swimming Halls’, Masters. Lund University.

Hea 05 Acoustic performance (2016) Available at https://www.breeam.com/BREEAMUK2014SchemeDocument/content/05_health/hea05.htm (Accessed on 25 March 2018)

International WELL Building Institute (2016) ‘The WELL Building Standard’. Available at https://www.wellcertified.com/sites/default/files/resources/WELL%20Building%20Standard%20-%20Oct%202014.pd (Accessed on 24 March 2018)

IOA and ANC (2015) ‘Acoustics of Schools: a design guide’, Building Bulletin, 93(November, 2015), p. 111.

Jensen, K. L. L., Arens, E. and Zagreus, L. (2005) ‘Acoustical quality in office workstations, as assessed by occupant survey’, Indoor Air 2005, pp. 2401–2405. Available at: https://escholarship.org/uc/item/0zm2z3jg%0Ahttp://www.cbe.berkeley.edu/research/pdf_files/Jensen2005_IndoorAir.pdf.

Joseph, A. and Ulrich, R. (2007) ‘Sound control for improved outcomes in healthcare settings’, The Health Center for Health Design, (Issue paper no. 4), pp. 1–15.

Shield, B. and Dockrell, J. (2003) ‘Psychology and Human Development, Institute of Education, London University, 25 Woburn Square, London WC1H 0AA’, Building Acoustics, 10(2), pp. 97–106.