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As part of the acoustic design reviews we carry out we always look for value engineering opportunities. We can often save our clients a significant amount of money by ensuring that materials are only specified where required.

Please see below 10 common value engineering opportunities in the design of new residential developments:

1) Acoustic resilient layers in addition to EPS insulation in concrete floors:
Where floors are constructed from precast or in situ concrete slabs, an EPS thermal layer under a floating screed will normally provide the required impact sound insulation. A dedicated acoustic resilient layer is therefore not normally required.
2) Extra acoustic insulation in walls or floors:
As a general rule, it is not worth adding more than 25mm of mineral wool into a wall or floor cavity that is smaller than 100mm and more than 50mm of mineral wool in a cavity that is more than 100mm. The additional benefit of thicker insulation is marginal and therefore generally not cost affective.
3) Acoustic insulation in internal walls:
Insulation is not necessary within internal walls within dwellings provided that you have room to use a 70mm stud. The following wall construction is compliant with Building Regulations Part E requirements and is often much easier/quicker/cheaper to install onsite that a thinner wall containing acoustic insulation: 12.5mm high density plasterboard (min. surface mass 10.6kg/m2) either side of a 70mm metal C-stud.
4) Reverberation control in common areas:
Building Regulations Part E requires that reverberation control is provided in communal areas (corridors etc). However, reverberation control is only strictly required in communal areas that provide <strongdirect access to dwellings. Communal areas that do not contain apartment front doors do not need to be treated. This generally means that reverberation control is not required in entrance lobbies or stairwells.</strong
5) Attenuators in MVHR systems:
Attenuators are often over-specified in MVHR or MEV systems. As a general rule it is not necessary to include attenuators in ducting between MEV/MVHR units and external supply inlets and discharge outlets. If attenuators are required between the MEV/MVHR units and habitable rooms it may be more cost effective to upgrade the MEV/MVHR units to quieter models (see below) rather than use the attenuators. Some attenuators also only offer poor sound attenuation and therefore are not cost effective.
6) Acoustic resilient layers in hotels or student accommodation:
Carpet can be used to control impact sound within hotels or student accommodation because the building operators will have control of floor finishes. Therefore, a dedicated acoustic resilient layer may not be required.
7) ‘Acoustic’ products:
We sometimes come across ‘acoustic’ products that claim to have special ‘acoustic’ properties. Often the benefit of these materials is marginal at best. Sometimes the claims are simply wrong. If in doubt contact Cass Allen for an impartial view.

So what do you do with all those cost savings? Well, there are some areas where we generally recommend spending that little bit extra. The following items are normally recommended to improve the development and may save money in the long-term by preventing noise-related complaints from future occupants:

8) Independent wall liners to lift shafts, stairwells and bin stores:
Lifts tend to be well isolated these days however complaints regarding structure-borne lift noise do sometimes occur. We therefore generally recommend installing independent wall liners to any walls separating habitable rooms from lift shafts. Independent wall liners minimise the likelihood of complaints and subsequent expensive investigations and remedial works. We also recommend independent wall liners to bin stores and stairwells where regular impacts on the separating walls may also occur.
9) Over-sized MVHR units:
Noise levels generated by MVHR units can vary considerably when moving the same quantity of air. A smaller MVHR unit will have to spin faster and work harder than a larger unit and this leads to more turbulence and higher levels of noise. A doubling of fan speed results in a ~16 dBA increase in noise. It is therefore often worth spending a bit of extra money on larger MVHR units that can comfortably achieve required airflow rates. This is particularly cost effective if it means that attenuators or acoustic duct lagging are not required or if it prevent future complaints from residents.
10) Anti-vibration mounts for pipework in plant rooms:
Pipework in plant rooms is often hung directly from the slab above. Structure-borne noise from the pipework can be audible in the rooms above and consequently provoke complaints from affected residents. Where residents are located above plant rooms, we recommend installing the pipework on anti-vibration mounts/hangers to minimise the likelihood of complaints and/or subsequent expensive investigations and remedial works.

We hope you find the above examples useful. Please get in touch if you would like to discuss any of the above examples or if you would like us to review any of your projects in more detail.

Whenever a new development is built, it impacts the way in which wind moves through an area. This is not a consideration that you may immediately associate with acousticians, however, in tall buildings with certain types of façade elements, it can be a real acoustic problem.

Wind flow across any building will generate noise – this is due to turbulent airflow around the edges of the building. At higher wind speeds this is generally audible as a broadband or slightly tonal ‘wooshing’ sound. People are generally familiar and accustomed to this noise and therefore it is rarely considered to be a problem.

However, under certain conditions, wind can cause building elements to vibrate which can potentially generate high noise levels.

It is quite rare for this to be a problem, however, when it is, it can be quite dramatic.

The weird ‘alien like’ sound that can be heard in the video is caused by the vibration of the ‘blades’ on the roof of the building. This vibration occurs at certain wind speeds and directions.

Smaller façade elements tend to be most susceptible to tonal wind induced noise, such as architectural baguettes, solar shades, cables, small apertures etc. This is because the natural resonant frequency of these objects are more likely to be in the audible frequency range (20-20,000Hz).

There are general guidelines that can be followed to minimise the risk of vortex shedding problems in the design of new buildings:

• Any circular façade elements with a diameter of less than 50mm should be avoided where possible.
• Where small façade elements are required, ensure the façade elements are sufficiently damped and consider modifying the design of the façade elements to break up vortices (this can be achieved by adding fins or other design features designed to break up vortices).
• If repeated façade elements form part of the development design, they should be spaced irregularly to avoid periodic vortices becoming established.

Testing and modelling can also be carried out to further assess whether any issues are likely to occur including:

a) Modelling the façade elements using Computational Fluid Dynamic (CFD) software or;

b) Conducting tests of the façade elements in a wind tunnel.

If you would like guidance relating to tonal wind induced noise or any other acoustic aspect of your project, please contact us and we would be happy to assist.

If you’ve found this article interesting, have a look at these other examples of vortex shedding occurring in various contexts; some of them are quite dramatic!

The fall of the Tacoma Bridge

Cloud formations around madeira

Lamp posts dancing on the M62

Aeolian Harp – an instrument that sings in the wind as a result of vortex shedding

Mechanical ventilation noise is a common cause of complaints in new-build residential developments where continuously running MVHR and MEV systems are used (i.e. System 3 or System 4 from Building Regulations Part F). Most new urban developments are ventilated using these systems.

MVHR can be most problematic, as supply air ducts run directly to noise-sensitive rooms (bedrooms and living rooms), however noise from continuously running extract systems in wet room (bathrooms and kitchens) also have the potential to annoy residents, particularly in open plan kitchen/dining/living rooms.

1. Specify noise limits

MVHR and MEV systems should be specified to achieve acceptable noise levels in habitable rooms. Building Regulations Part F states that, to ensure good acoustic conditions, mechanical ventilation noise should not exceed the limits given in table 1 below. These limits should be achieved with the units running at background ventilation rates as a minimum. However, in some cases it may be appropriate to specify systems to achieve the limits in boost mode.

For high value or particularly sensitive properties, it may be appropriate to adopt lower project noise limits.

Table 1 – MVHR/MEV Noise Criteria in Building Regulations Part F

Room	Noise Limit
Bedrooms and living rooms	30 dB LAeq,T
Less sensitive rooms such as kitchens and bathrooms	35 dB LAeq,T

2. Careful design

The systems should be carefully designed to ensure that the noise limits are achieved. M&E designers and equipment manufacturers should be asked to confirm that their designs are capable of achieving the noise limits specified as per item 1 above. Cass Allen can review designs where a second opinion is required.

The following noise mitigation measures are recommended as a minimum:

• Inherently quiet MEV/MVHR units should be selected. Units should not be undersized. The specification of cheaper, undersized units is a common cause of unacceptably high MEV/MVHR noise levels. Noise should be one of the main considerations in the selection and sizing of the units. A larger unit run at a lower speed will be significantly quieter than a smaller unit running at a higher speed.
• Fan units should be installed on appropriate anti-vibration mounts and pattresses. There should be no rigid connections between the units and the building structure.
• Duct layouts should be carefully planned with no unnecessary bends in the system. Changes in duct size and shape should be avoided wherever possible.
• Rigid ducting should be used for duct runs (flexible ducting has a much higher resistance to airflow and, where possible, should not be used). Joints between rigid ducting should be mechanically fixed, silicon sealed and/or taped to ensure an airtight seal.
• Where the ducting penetrates walls, the hole in the wall for the ducting should be as small as possible and any gaps between the ducting and the wall should be sealed airtight with a suitable non-setting mastic.
• Diffusers and dampers should be carefully selected to ensure that they will not generate high levels of turbulent noise at the required air flow velocities. Dampers should be located a minimum of 3 (and preferably 5 to 10) duct diameters away from room grilles if possible.

The system should be designed so that the air flow does not exceed the following velocities in ducting, depending on which internal noise limits given in table 1 have been adopted:

Table 2 – Maximum flow velocities in MEV/MVHR systems

Additional mitigation may also be required depending on the design of the system, including:

• In-line attenuators
• Lagging of ductwork above sensitive rooms
• Acoustic enclosures for MEV and MVHR units

3. Installation

Poor installation is a common cause of noise complaints from MEV / MVHR systems. Use of flexible ductwork, unsupported ductwork, unnecessary bends, sharp bends, bodged or poor connections would all result in higher levels of resistance in the system and therefore the MEV/MVHR units would need to be run at higher duties to provide the required air flow rates. This would result in significant increases in noise levels from the MEV/MVHR units and turbulent noise generated by airflow through the system.

We recommend that BPEC approved installers are chosen for installation work to minimise the risk of poor installation.

4. Commissioning

Given how critical installation quality is to the achieved noise levels, the commissioning testing is key to ensuring the system has been installed correctly.

We recommend that independent commissioning is carried out, including noise testing, to ensure that the noise limits are achieved.

Systems should be balanced for the lowest possible fan speed with dampers as open as possible.

As part of the testing, the systems should also be checked to ensure that the MEV/MVHR units are not being run at overly high speeds in order to compensate for poor installation i.e. the required unit duty onsite should be similar to the design duty.

5. Maintenance

Developers should pass on manufacturer recommendations to residents for cleaning and maintaining the MEV/MVHR systems. This is typically a guide outlining a service schedule that the residents can follow to ensure the systems are kept clean and in good working order.

If residents do not maintain the systems, then they will invariably become less efficient and noisier over time.

Sound insulation testing is required on a huge number of sites across the UK in order to show that buildings are compliant with Building Regulations. This video shows exactly what goes into a sound insulation test as well as a few common obstacles encountered by sound testers on sites every day.

The recent increase in popularity of MUGAs across the country has led to a rise of noise-related issues associated with their use. There is little in the way of official guidance for the assessment of MUGA noise affecting nearby residents and so it is generally appropriate to employ a pragmatic, common sense approach to any assessment.

The following 5 noise mitigation strategies are commonly employed to control MUGA noise emissions and minimise the potential for complaints:

• 1. Distance

  The main and most obvious method of reducing the noise impact of MUGAs is to site them as far as possible from nearby residents. The closer MUGAs are to dwellings, the higher the likelihood of complaints. Fields in Trust’s document “Planning and Design for Outdoor Sport and Play” recommend that MUGAs are located a minimum of 30m from the nearest residential property wherever possible. Achieving this 30m is often difficult or not possible for many developments we work on in London and other built up areas where space is at a premium. In these cases, physical mitigation and careful management are key to ensuring acceptable noise levels are achieved.

• 2. Physical Mitigation

  There are a number of mitigation measures that can be built into the MUGA design in order to minimise noise generation or transmission to the nearby dwellings:

  • Where space allows, installing barriers and bunds between the MUGA and dwellings can significantly reduce noise emissions. It should be noted that in order for these barriers to be effective they need to cut the line of sight between the residents and people using the MUGA. This often requires the barriers to be at least 3m high. Barriers of this height can be quite imposing and in some cases it may be necessary to strike a balance between noise impact and visual amenity.
  • Noise from balls impacting the MUGA fencing can be a significant source of MUGA noise emissions. Wherever possible it is recommended that the panels are constructed of perforated sheet metal or weld mesh in place of a chain-link type fence in order to reduce rattle and ball impact noise. It is also important that anti-vibration (AV) bushings are used to fix the fence panels to the supports. These bushings acoustically dampen the panels and minimise structure-borne noise transmission, which has the effect of reducing the magnitude and duration of the impact noise.

• 3. Maintenance

  Poorly maintained MUGAs will generally generate significantly more noise than well maintained ones. This is due to a number of factors including damaged panels, loose brackets, worn AV bushings and squeaky gates.

• 4. Hours of Use

  Night-time use of MUGAs is significantly more likely to disturb nearby neighbours than use during the day. Where MUGAs are privately managed this is easily controlled however where MUGAs are intended for public use it can be difficult to ensure that they are only used during the intended hours. One method of naturally controlling hours is to limit artificial lighting, meaning that the MUGA is less likely to be used when it gets dark. However, this carries security risks and should be determined on a case-by-case basis.

• 5. Residents’ Engagement

  Where a new MUGA is proposed close to existing residential properties, a powerful method of reducing the potential noise impact on nearby residents is to ensure that the local community are engaged with the proposals as far as possible. This can be achieved by educating residents on the benefits of MUGAs, making them aware of plans at an early stage and, of course, ensuring that local residents have access to the MUGAs and a simple method of reporting misuse or damage.

We hope you find the above useful. Cass Allen has extensive experience in MUGA noise impact assessments and we have a detailed archive of MUGA noise data that can be used to help inform the design, placement and management of these important facilities. If you would like any further advice or help then please don’t hesitate to get in touch.

Councils in London and elsewhere are increasingly asking for detailed assessments of ground-borne noise where developments are located close to railways and other sources of vibration.

Ground or structure-borne noise is noise in the audible frequency range (approximately 20Hz – 16 KHz) than is transmitted as vibration and then reradiated into rooms as noise.

With railways, ground and structure-borne noise tends to be dominant at around 100Hz. This is perceived as a low frequency rumble as trains pass by. Most of us will have experienced this at one time or another when in a building near a railway.

For new residential developments, this rumble has the potential to disturb future occupants. Particularly during the night-time when residents will be most sensitive to noise.

Unfortunately, there are currently no UK or international standards for the assessment of ground-borne noise affecting new residential developments. The most relevant guidance is that given in the Association of Noise Consultants guideline – Measurement and assessment of ground-borne noise and vibration. The ANC guideline summarises current research and guidance from elsewhere.

One of the guidance documents referenced in the ANC guideline was published by the American Public Transit Association (APTA). This suggests criteria for acceptable maximum levels of ground-borne noise affecting various building types, including a criterion of 35 dB LAmax for ground-borne noise affecting residential properties. This criterion is increasingly being adopted (as 35 dB LASmax) by Councils when defining acceptable ground-borne noise levels for new developments.

In our view 35 dB LASmax represents a good standard but it may actually be acceptable for ground-borne noise levels to exceed this limit, depending on other factors such as the frequency of events (e.g. train passes) and the range of maximum noise levels that occur.

There are various treatments that can be adopted to reduce ground-borne noise affecting new developments. However, where significant ground-borne noise levels are present, full structural anti-vibration bearings are likely to be required. These are typically rubber or spring bearings that are used to isolate the building structure near ground level.

Spring bearing on a steel framed building

Elastomeric rubber bearing on steel framed building

Images provided by Mason UK (bearing manufacturer and supplier)

Such treatments carry significant cost, risk, design and program implications. It would not be unusual for the treatment of a medium sized block of apartments next to a railway in London to cost £100-150K in bearing costs alone. There is also the associated costs in design work, added costs to the structure and additional construction work onsite. Bearings also add complexity to the design that increases the risk of construction errors or timetabling issues. It is therefore important to ensure that bearing treatments are only used where strictly necessary.

Given the implications of such treatments, it is always advisable for developers to establish ground-borne noise levels and Council requirements early on where development sites are located near to railways or any other significant sources of vibration. In this way any required treatments can be assessed and properly costed and budgeted for.

Amendments made to The Town and County Planning (General Permitted Development) (England) Order 2015 will have a significant impact on how developers approach Class MA (office to residential) permitted developments.

In a move that was widely expected by many in the industry, The Permitted Development order has now made permanent the existing rights to convert existing offices buildings for residential use. However, an additional criterion has been added, stating that the Local Planning Authority (LPA) must consider the ‘Impacts of noise from commercial premises on the intended occupiers of the development’ when assessing applications. Previously this was not a consideration and there was no mechanism in place for LPAs to refuse applications on noise grounds.

The reason for this criterion is principally as a result of campaigns on behalf of licenced premises and two specific documents: the ‘London Grassroots Music Venues Rescue Plan’ and the ‘Bristol Live Music Census Report’. Both reports and the campaigns cite that the permitted conversion of offices into residential properties have resulted in noise sensitive receptors (i.e. residents) being introduced into areas where there are long established music venues or other sources of noise. This, in turn, has given rise to noise complaints from the new residents and the LPA imposing additional constraints on the music venue or noise source. This is seen as unfair and a potential threat to the night time economy of the UK.

Although the requirement to assess noise impact has been welcomed by campaigners, this move falls short of the ‘Agent of Change’ principle which had been campaigned for. The agent of change principle seeks to place the responsibility for noise mitigation measures on the incoming noise sensitive use, not the premises generating the noise.

It should be noted that although the wording of the amendment does not oblige the LPA to apply the Agent for Change principle, it does not preclude it either. The lack of clarity has been highlighted in a recent debate in the House of Lords in which ministers were called upon to provide further guidance. It will be interesting to see what further information is provided in the coming months.

The discussion surrounding noise and permitted developments touches on a wide range of legal and ethical questions, and the answers may not be as straightforward as they seem.

Given the lack of clarity in the guidance, it is advisable for developers to contact the Local Authority prior to submitting a Class MA permitted development application to fully understand their requirements with respect to noise.

If you have an upcoming Class MA permitted development application and you are concerned about these recent changes to legislation, please contact us.