Showing posts with label 4. Sound Insulation. Show all posts
Showing posts with label 4. Sound Insulation. Show all posts
4.1 Subjective Evaluation and Conversion between Rw and Dw
Sound Insulation
Sound insulation describes the reduction in sound across a partition. The sound insulation across a good conventional, lightweight, office to office construction is typically in the order of 45 dB Dw. This means that if the sound level in the source room is in the order of 65 dB, (a typical level for speech) the sound level in the adjacent room, the receiver room, will be in the order of 20 dB (barely audible). If sound levels are increased in the source room to 75 dB (raised voice), sound levels within the adjacent room will also increase to around 30 dB (audible). Sound insulation therefore describes the level of sound lost across a partition and not the level of sound within a room.
Privacy
Privacy describes the perceived sound reduction across a wall. Privacy is a function of both sound insulation and background noise. Background noise is a function of services noise and noise break-in through facades or open windows, vents etc.
If the background noise within a room is increased by 5 - 10 dB, the perceived level of privacy across a partition is also increased by 5 to 10 dB. Therefore, when looking at required sound insulation levels on-site, it is important to consider both the background noise in the receiver room and the sound insulation reduction across the partition.
Subjective Description of Sound Insulation
The table to the right provides an illustrative representation of privacy. This table specifies the two Dw levels of the partition, Column 1. Two levels are provided in this column, one for background noise levels of 35 dBA, 1, and the other for background noise levels of 40 dBA, 2. Please see the text above for an explanation.
Rw (Lab Tested Sound Reduction Index) and Dw (On SIte Sound Reduction Index)
Two parameters are used to describe the sound insulation of a partition; Dw and Rw. Dw represents the sound insulation of a partition on-site. Since these figures describe the final site requirements, Dw levels are specified by clients and Building Regulations. Rw represents the lab tested sound insulation of a product wall type/floor type. Due to flanking and other factors, lab rated sound reduction levels will not be achieved on-site. Conventionally, there is a 5 to 10 dB reduction between a Rw lab tested figure and an on-site Dw figure. The conversion between Dw and Rw is relatively complex and takes into consideration receiver room volume, receiver room reverberation times and the area of the separating partition. The conversion between Rw and Dw should always be calculated.
Sound insulation describes the reduction in sound across a partition. The sound insulation across a good conventional, lightweight, office to office construction is typically in the order of 45 dB Dw. This means that if the sound level in the source room is in the order of 65 dB, (a typical level for speech) the sound level in the adjacent room, the receiver room, will be in the order of 20 dB (barely audible). If sound levels are increased in the source room to 75 dB (raised voice), sound levels within the adjacent room will also increase to around 30 dB (audible). Sound insulation therefore describes the level of sound lost across a partition and not the level of sound within a room.
Privacy
Privacy describes the perceived sound reduction across a wall. Privacy is a function of both sound insulation and background noise. Background noise is a function of services noise and noise break-in through facades or open windows, vents etc.
If the background noise within a room is increased by 5 - 10 dB, the perceived level of privacy across a partition is also increased by 5 to 10 dB. Therefore, when looking at required sound insulation levels on-site, it is important to consider both the background noise in the receiver room and the sound insulation reduction across the partition.
Subjective Description of Sound Insulation
The table to the right provides an illustrative representation of privacy. This table specifies the two Dw levels of the partition, Column 1. Two levels are provided in this column, one for background noise levels of 35 dBA, 1, and the other for background noise levels of 40 dBA, 2. Please see the text above for an explanation.
Rw (Lab Tested Sound Reduction Index) and Dw (On SIte Sound Reduction Index)
Two parameters are used to describe the sound insulation of a partition; Dw and Rw. Dw represents the sound insulation of a partition on-site. Since these figures describe the final site requirements, Dw levels are specified by clients and Building Regulations. Rw represents the lab tested sound insulation of a product wall type/floor type. Due to flanking and other factors, lab rated sound reduction levels will not be achieved on-site. Conventionally, there is a 5 to 10 dB reduction between a Rw lab tested figure and an on-site Dw figure. The conversion between Dw and Rw is relatively complex and takes into consideration receiver room volume, receiver room reverberation times and the area of the separating partition. The conversion between Rw and Dw should always be calculated.
4.2 Sustainability and Sound Insulation
Sound insulation is not a subject often considered an influential factor during the design stage of green and sustainable buildings. Sound insulation can significantly impact upon the levels of embodied energy in a given building. It is therefore important to have a clear understanding of how sound insulation can affect levels of embodied energy.
Refurbishment
The most effective method of reducing the embodied energy of a given development is to re-use an existing building. Demolition and rebuilding is often justified on the grounds of flexibility and acoustics. Our experience across large and complex refurbishment projects shows that most problems can be overcome and resolved in a cost effective manner. The key to refurbishments is in understanding the performance of the existing building fabric by means of early upfront acoustic testing. Having established the existing performance and understood the limitations and restrictions of a given building frame, design teams can work their way around these restrictions.
Lightweight versus Mass
Heavy/high mass buildings are often favoured on the grounds of enhanced acoustics; however timber and other lightweight framed buildings can often offer equal performance. The advantage of timber/lightweight framed buildings is the considerable reduction in embodied energy with a sustainable building frame and reduced levels of flanking between spaces.
Comparing the acoustic performance of stud to block work, it is seen that both of these systems have a similar performance. Block work does have a better low frequency performance but this is rarely required in modern developments. Timber studs tend to offer lower levels of sound insulation than metal studs, as timber studs are less flexible. This limitation can be overcome by means of using a resilient bar within the partition make up. For comparison, the acoustic performance of walls and floor types are covered over the next two sections.
Mineral Wool within Partitions
Acoustic dampening within stud walls is a cost effective and sustainable method of enhancing the performance of a partition. ISO wool is conventionally used within partitions. This is a quarried product and one which requires considerable heat to turn rock into wool. Damping within partitions can be achieved by most forms of lightweight fibrous or fluffy materials. This means that a wide range of recycled / sustainable materials can be used: recycled carpets, recycled plastic bottles, recycled jeans, Thermo fleece - sheeps wool, Warmcell - recycled news papers, etc.
Performance
As a rule of thumb, a ±6 dB change in sound insulation equates to a halving or doubling of mass of a given construction. Over specifying acoustic parameters can therefore have a significant impact upon waste.
It is often the case that performance standards are copied from one project to another, particularly in the case of office developments. Performance standards are repeatedly misunderstood and hence over specification takes place. Planning conditions are another type of performance requirement that are rarely challenged, which again can lead to over specification. All of these factors results in waste and unnecessary levels of raw materials being used. When designing sustainable buildings it is fundamental to ensure that the correct and most suitable performance requirements are used.
It is important to note that small reductions in acoustic performance levels are often not heard. A small variation or reduction in performance levels can however considerably reduce the required levels of acoustic treatment, remembering the 6dB rule. It is therefore sometimes worth considering downgrading the performance levels of the floors and walls on the grounds of sustainability.
An important rule is that a partition should only exceed the performance of the weakest link by no more than 10 dB. As an example, there is no point in having a partition rated above 40 dB Rw if it contains as 30 dB Rw door. The above text shows that by having tight, accurate performance requirements, waste can be considerably reduced. Hence, it is always worth consulting with an acoustic engineer when considering performance specification.
Specification Design Tolerances & Early Testing
When designing a building, an acoustic consultant will usually include significant design tolerances. One way to reduce the effects of these tolerances is to carry out a programme of early acoustic testing. This is a very good method of ensuring that the design is sufficient and gives enough time for any design tweaks to be made with minimal cost impact on other areas of design. This will allow design tolerances to be reduced with the comfort of knowing that the design will be assessed at an early stage. The benefit of this is a reduction in over specification, resulting in less waste, less embodied energy and less cost to the client.
Refurbishment
The most effective method of reducing the embodied energy of a given development is to re-use an existing building. Demolition and rebuilding is often justified on the grounds of flexibility and acoustics. Our experience across large and complex refurbishment projects shows that most problems can be overcome and resolved in a cost effective manner. The key to refurbishments is in understanding the performance of the existing building fabric by means of early upfront acoustic testing. Having established the existing performance and understood the limitations and restrictions of a given building frame, design teams can work their way around these restrictions.
Lightweight versus Mass
Heavy/high mass buildings are often favoured on the grounds of enhanced acoustics; however timber and other lightweight framed buildings can often offer equal performance. The advantage of timber/lightweight framed buildings is the considerable reduction in embodied energy with a sustainable building frame and reduced levels of flanking between spaces.
Comparing the acoustic performance of stud to block work, it is seen that both of these systems have a similar performance. Block work does have a better low frequency performance but this is rarely required in modern developments. Timber studs tend to offer lower levels of sound insulation than metal studs, as timber studs are less flexible. This limitation can be overcome by means of using a resilient bar within the partition make up. For comparison, the acoustic performance of walls and floor types are covered over the next two sections.
Mineral Wool within Partitions
Acoustic dampening within stud walls is a cost effective and sustainable method of enhancing the performance of a partition. ISO wool is conventionally used within partitions. This is a quarried product and one which requires considerable heat to turn rock into wool. Damping within partitions can be achieved by most forms of lightweight fibrous or fluffy materials. This means that a wide range of recycled / sustainable materials can be used: recycled carpets, recycled plastic bottles, recycled jeans, Thermo fleece - sheeps wool, Warmcell - recycled news papers, etc.
Performance
As a rule of thumb, a ±6 dB change in sound insulation equates to a halving or doubling of mass of a given construction. Over specifying acoustic parameters can therefore have a significant impact upon waste.
It is often the case that performance standards are copied from one project to another, particularly in the case of office developments. Performance standards are repeatedly misunderstood and hence over specification takes place. Planning conditions are another type of performance requirement that are rarely challenged, which again can lead to over specification. All of these factors results in waste and unnecessary levels of raw materials being used. When designing sustainable buildings it is fundamental to ensure that the correct and most suitable performance requirements are used.
It is important to note that small reductions in acoustic performance levels are often not heard. A small variation or reduction in performance levels can however considerably reduce the required levels of acoustic treatment, remembering the 6dB rule. It is therefore sometimes worth considering downgrading the performance levels of the floors and walls on the grounds of sustainability.
An important rule is that a partition should only exceed the performance of the weakest link by no more than 10 dB. As an example, there is no point in having a partition rated above 40 dB Rw if it contains as 30 dB Rw door. The above text shows that by having tight, accurate performance requirements, waste can be considerably reduced. Hence, it is always worth consulting with an acoustic engineer when considering performance specification.
Specification Design Tolerances & Early Testing
When designing a building, an acoustic consultant will usually include significant design tolerances. One way to reduce the effects of these tolerances is to carry out a programme of early acoustic testing. This is a very good method of ensuring that the design is sufficient and gives enough time for any design tweaks to be made with minimal cost impact on other areas of design. This will allow design tolerances to be reduced with the comfort of knowing that the design will be assessed at an early stage. The benefit of this is a reduction in over specification, resulting in less waste, less embodied energy and less cost to the client.
4.3 Performance Specifications
This illustration presents the required performance standards for partitions to meet BB93, HTM and BREEAM office requirements for a range of cellular spaces.
The provided performance targets are given in terms of the Rw levels. Assumptions relating to room sizes, floor to ceiling height, room acoustic finishes and other factors have been made during the conversion between Rw and Dw levels specified BB93, HTM and BREEAM. These assumptions do not apply to all developments; hence this information should be used as guidance only. Please consult with an acoustic consultant for accurate levels.
The provided performance targets are given in terms of the Rw levels. Assumptions relating to room sizes, floor to ceiling height, room acoustic finishes and other factors have been made during the conversion between Rw and Dw levels specified BB93, HTM and BREEAM. These assumptions do not apply to all developments; hence this information should be used as guidance only. Please consult with an acoustic consultant for accurate levels.
4.6 Sound Insulation Details & Service Penetrations
One of the key factors affecting the acoustic performance of separating elements is the acoustic performance of details, flanking elements and services penetrations. It is vital that these elements are addressed carefully.
Flanking and Junctions – Flanking is an important point to consider during the design stages. For high performance buildings, an acoustic consultant should be appointed. Sections 4.7 - 4.10 provide a range of details.
Sealing junctions - As a rule of thumb, all junctions and joints should be sealed with non-hardening mastic. Any holes smaller than 5mm can be sealed with mastic. Large holes should be sealed with plasterboard or mortar as appropriate.
Resilient bars are an important method of boosting the performance
of stud walls. Care must be taken to ensure that the flexibility of the resilient bar is not breached. See sections 4.8 and 4.10.
Services are one of the major reasons for short falls in sound insulation and this is usually due to the poor layout of services during the design stages. It is vital to consider service runs, location of crosstalk attenuators and penetration details. See sections 4.9 and 4.10.
Structures are often overlooked during the design stage. If not considered, details around partitions can become difficult to make good.
Site Construction Details - Having worked across many sites, there are many common faults which have been observed. Most issues relate to services, see sections 4.9 and 4.10.
Flanking and Junctions – Flanking is an important point to consider during the design stages. For high performance buildings, an acoustic consultant should be appointed. Sections 4.7 - 4.10 provide a range of details.
Sealing junctions - As a rule of thumb, all junctions and joints should be sealed with non-hardening mastic. Any holes smaller than 5mm can be sealed with mastic. Large holes should be sealed with plasterboard or mortar as appropriate.
Resilient bars are an important method of boosting the performance
of stud walls. Care must be taken to ensure that the flexibility of the resilient bar is not breached. See sections 4.8 and 4.10.
Services are one of the major reasons for short falls in sound insulation and this is usually due to the poor layout of services during the design stages. It is vital to consider service runs, location of crosstalk attenuators and penetration details. See sections 4.9 and 4.10.
Structures are often overlooked during the design stage. If not considered, details around partitions can become difficult to make good.
Site Construction Details - Having worked across many sites, there are many common faults which have been observed. Most issues relate to services, see sections 4.9 and 4.10.
4.11 Impact Isolation
Impact isolation is the prevention of foot-fall noise, chair scrapes and the transmission of other noise sources as a result of direct impact with the building structure.
It is more often the case that the mass of the building (even concrete framed buildings) does not provide adequate acoustic protection to mitigate against impact noise. The solution is to add a resilient layer within the floor make up. The resilient layer in most instances can be carpet or acoustic lino (depending on performance requirements). Alternatively, a polyurethane or isolation sheet is located under a floor finish or screed. With this method of isolation, it is important to ensure that the floating layer or screed does not make contact at any point with the building structure. It is therefore essential to install the correct edge detail and follow all other requirements specified by the resilient layer manufacturer.
It is more often the case that the mass of the building (even concrete framed buildings) does not provide adequate acoustic protection to mitigate against impact noise. The solution is to add a resilient layer within the floor make up. The resilient layer in most instances can be carpet or acoustic lino (depending on performance requirements). Alternatively, a polyurethane or isolation sheet is located under a floor finish or screed. With this method of isolation, it is important to ensure that the floating layer or screed does not make contact at any point with the building structure. It is therefore essential to install the correct edge detail and follow all other requirements specified by the resilient layer manufacturer.
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