In spite of the obvious benefits of keeping dwellings well away from industrial uses, increasing pressure on land and the drive for more housing has meant that residential development close to industrial uses is becoming ever more common.

Local planning authorities (LPAs) often resist such schemes on noise grounds. Their argument being that the legal onus (under the Environmental Protection Act 1990 (EPA)) would be on the industrial use to reduce noise should future residents complain about industrial noise once they have moved in. This can place unreasonable constraints and/or financial burdens on industry and in some cases has resulted in closure and the loss of employment.

However, more recently there have been signs from government that residents moving into developments near industrial uses may be expected to accept that some noise is inevitable. This is reflected in the softening of planning guidance regarding the definition of what constitutes a statutory nuisance, which in effect, reduces the requirement for local authorities to take legal action under the EPA (see http://planningguidance.communities.gov.uk/blog/guidance/noise/noise-guidance/ para 007).

Moving in the opposite direction, a recently revised British Standard (BS4142:2014) has, for the first time, required that an assessment be made on dwellings proposed near existing industrial uses. The problem with BS4142 is that it only assesses noise external to a proposed dwelling and therefore does not take into account any mitigation that can be incorporated into the façade (eg high performance glazing or mechanical ventilation etc). As a result, most proposed dwellings proposed near industrial uses will fail to achieve a satisfactory BS4142 rating, which provides support for any LPA wishing to refuse such an application.

Our experience is that a reasonable compromise can often be negotiated with LPAs based on a combination of layout/landscaping together with façade mitigation designed to ensure that internal noise levels achieve suitable standards (typically as set out in BS8233:2014). Typical mitigation strategies are briefly discussed below:

1) Site layout

Whilst it is good practice to keep dwellings as far as possible from the boundary with an industrial site, noise does not reduce quickly with increasing distance. It is therefore normally not practical to rely on distance alone to reduce the industrial noise. However, all else being equal, placing playgrounds or public amenity land on the boundary is beneficial acoustically, especially when incorporating an appropriately designed acoustic barrier/bund on the boundary line.

Of potentially more benefit, is locating terraced houses or flats on the boundary to act as an acoustic barrier for the rest of the site. This requires careful façade and amenity space design but can help to maximise land usage.

2) Landscaping

It is a common misconception that trees/bushes act as acoustic barriers. In fact, bands of trees/bushes up to around 25m deep have no significant acoustic properties. However, the visual screening they provide can often help residents to believe that the noise is less and so they do have a psychological value. An effective acoustic barrier needs to be imperforate and of sufficient surface mass so that the sound travelling through it is insignificant compared with the sound travelling over the top (typically a minimum surface mass of 10-12kg/m2 is required). Tall wooden barriers can be effective but can also be visually dominating. Earth bunds are very effective, but can take up too much space, and so a small bund combined with a smaller wooden barrier on top is often adopted.

3) Façade design

The weakest parts acoustically of a typical dwelling are the glazing and the ventilation. Both of these can generally be specified to achieve whatever is required to achieve satisfactory internal noise levels. Typically a noise survey will be carried out to quantify the industrial noise and then the glazing and ventilation will be specified accordingly. Matters can be complicated by solar gain and overheating issues, but our experience is that façade design is normally fairly straightforward.

4) Negotiation with the industrial user

Often it is tempting to try and reduce the noise at source through negotiation with the industrial user. Whilst this can be effective, especially if the noise is caused by a well-defined source that is readily mitigated or replaced (eg an old compressor or fan, where replacement would be much cheaper than noise control to the residential scheme and where the prospect of new machinery would be a tempting incentive for the industrial user to co-operate). However, for large industrial sites that contain many noise sources or where the noise source is not immediately apparent (eg noise breakout through large industrial sheds) our experience is that mitigating the industrial noise is often problematic both technically and in terms of logistics. Clients also are legitimately concerned than once they become dependent upon the industrial user their negotiating position becomes weaker.

As with many aspects of acoustics, early integration of an acoustician into the planning team is essential when considering a residential development near an existing industrial use. 

 

 

It’s a quirky English phenomenon that, during advert breaks for Coronation Street or Eastenders, a large proportion of the country decides to make a cup of tea.

It’s a race against time – you have around 3 minutes to boil the kettle, suitably stew the tea bag, add the milk (do you take sugar?) and get back to the settee in time to ensure you don’t miss the next plot twist.

Kettle manufacturers are conscious of this predicament, with kettles being designed to boil water as quickly as possible. Most UK kettles draw 3Kw, which is at the limit of what domestic plugs can handle and roughly the electricity generated by 21m² solar panels in full sunlight.

With approximately 1.5-1.75 million kettles being boiled during any single advert break – this needs a lot of power!

This puts a huge and sudden demand on the national power grid that the larger power stations can sometimes struggle to meet. In fact, national grid employees watch TV to help them prepare for the surges as best they can, as shown in this recent documentary.

To help solve this problem at a local level, a number of smaller and more reactive biodiesel and gas power generation sites are increasingly being installed around the country. These facilities can ramp up quickly as required to support the power supply in a given area; a flexible solution to a very British problem!

One potential drawback of these systems is the noise output from their generators – which can be significant. Careful acoustic design and planning is therefore crucial to ensure that nearby residents are not disturbed and applications for new sites run smoothly.

Based on our experience, we have put together a list of factors that are important in the successful implementation of these sites.

1. Location

   Urban and rural sites present different challenges. Background noise levels tend to be higher in urban areas than in rural areas, which means that the noise from the generators will be less audible in urban areas.  However, it is likely that people will be living closer to the generators. Conversely, rural generator sites tend to be situated farther from residents, but background noise levels can be extremely low meaning that generator noise can be heard over a larger distance.

   The generators should always be placed as far as possible from residents; however other noise mitigation strategies are often also helpful.

2. Barriers

   Acoustic fences or bunds can be effective in reducing noise from the site. In general terms, the closer and higher the barrier is to the equipment, the more effective it will be. Additionally the design of the barrier (e.g. surface mass, number of gaps etc.) will also play a large part in the overall effectiveness.

3. Selection of Units

   It is recognised by the industry that the generators can be noisy. As such it is common for manufacturers to provide ‘low noise’ models or acoustic enclosures. Our experience is that, wherever feasible, this should be allowed for at the outset of the project given the nature of the noise and typical locations of the sites.

   Additionally, the more detailed the noise data provided by the manufacturers, the more accurate acoustic calculations can be. With detailed noise data we are able to carry out a value engineering exercise and explore using fewer or smaller barriers for example, whereas this may not be possible with only basic noise data.

4. Local Planning Authority Consultation

   Typically, the generators run sporadically and for only short periods. As such, stringent mechanical plant noise limits, which would be appropriate for more constantly running plant, are often not applicable for these sites. This means that design targets may potentially be relaxed, which would reduce the amount of physical noise mitigation required. It is important that the LPA are consulted as early as possible by a competent acoustician to negotiate the possibility of a relaxation to the design targets.

   Through appropriate calculations and 3D noise modelling, Cass Allen are able to advise on the feasibility of new schemes, optimise site layouts and design the size and location of noise barriers and other mitigation measures where required. In this way, we can help keep the noise impact of your cup of tea to a minimum.

It is becoming increasingly common for ‘screening rooms’ to be incorporated into developments to maximise their appeal.  With the recent debacle at this year’s Oscars, we thought it would be an appropriate time to offer some pointers on how to avoid other cinema-based blunders.

We have recently assessed the design of screening rooms in a range of developments including:

• Residential led mixed-use
• Hotels
• Care homes

In all of the above there are a number of common issues that should be considered as early as possible in the design stages to minimise the noise impact of the screening room on surrounding residents:

Location

Clearly, the further the screening room can be placed from residential rooms (or other potentially noise sensitive areas) the better. Ideally, there should be a ‘buffer’ of at least one non-habitable room between the screening room and any nearby residential room.

Partition Design

Where it is not possible to have buffer rooms then the next consideration will be to ensure that the partitions separating the two uses provide an adequate level of sound insulation.

It is typical for screening rooms to have loud sound systems installed.  Whilst that is great for the people watching the film, controlling noise (particularly low-frequency music or dramatic rumbles) is challenging in areas with limited space.

In general, the following design features should be adopted for all partitions separating screening rooms from adjacent apartments:

• Independent internal linings – wherever practical, the ceilings, floors and walls of the screening room should be completely independent or ‘acoustically isolated’ from the surrounding structure in order to avoid direct sound paths into adjacent residences.
• Deeper cavities and fibrous insulation – where cavities are formed in walls, floors and ceilings these should be made as wide/deep as possible. The deeper the cavity the more effective that partition will be at controlling low-frequency noise. There should also be at least 50mm of fibrous insulation in any cavity to further improve the acoustic performance.
• High mass layers – the partitions should be constructed from the heaviest materials practicable (i.e. multiple layers of dense plasterboard or dense concrete blockwork).

Where screening rooms are located close to residential areas, very high-performance partitions will be required and these can have significant implications on layouts, the structure and cost.

Hours of Use

Even with careful physical design and placement of the screening room, it will generally be necessary to limit the hours that the room can be used. Unlimited use of the screening room can quickly lead to complaints from residents, particularly at night when general background noise is lowest and people are more sensitive to noise.

Noise Limiters

It is possible to install noise level limiting equipment into screening room sound systems. This will stop users from turning the volume up beyond a pre-determined level, which will depend on the design and location of the room. This level should be set once all partitions and sound systems have been installed, and permanently adhered to thereafter.

Given the multiple issues involved in installing a screening room in a residential development, we would recommend seeking advice at an early stage from an acoustician with relevant experience.

Please get in touch if you would like any further information or have an upcoming project that you require specific guidance for.

Curtain walling is used on many of the larger residential developments we are involved in due to the construction and cost benefits.

The main acoustic issue with curtain walling is the potential for flanking sound transmission via the junction with separating walls and floors.

The type and design of curtain walling can vary significantly, however there are a few key elements required to ensure that sufficient sound insulation levels are achieved.

Please see below our top 5 details to watch out for.

 

1) Single mullions or transoms

In order to achieve high levels of sound insulation (e.g. between two adjacent residential units), at least two transoms will be required across separating floors, and two mullions will be required across separating walls. Where only one mullion or transom is provided, this will significantly reduce the achievable performance.

Example of single and double transoms at separating floor

2) Continuous mullions or transoms

Mullions or transoms can transmit noise along a façade very effectively, significantly limiting the achievable sound insulation. It is, therefore important to break mullions and transoms across separating floors and walls using flexible gaskets and to ensure there are no rigid fixings between them (including connecting brackets etc). Mullion or transom inserts may also be required where higher sound insulation levels are targeted.

Example of mullion & transom detailing at slab edge (section view)

3) Inadequate fire stopping across separating floors

Fire stops can be very helpful in providing acoustic insulation and often perform this dual role. To achieve high sound insulation levels across separating floors, the fire stopping should make an airtight seal between the slab edge and the façade as shown below. Fire stopping is typically formed from dense mineral wool and it’s important that it does not come loose overtime or as the building settles. Some products are better than others in this regard.

Good fire stopping is essential to acoustic performance

4) Noise ingress via spandrel panels

Spandrel panels in curtain walling are often formed of thermal insulation, sandwiched between two thin layers of aluminium. These panels provide very little airborne sound insulation and therefore can be an acoustic weak point in the façade, resulting in unacceptably high internal noise levels in developments located in noisier areas. It is normally straightforward to specify the build-up of spandrel panels once a survey has revealed the external noise levels that they need to deal with.

Noise ingress via spandrel panels

5) No ceilings

In all the examples so far, the ceiling is important in achieving higher sound insulation levels. In many developments we work on, commercial units or ancillary areas are located below residential units and do not have ceilings. In these cases, it is prudent to box in the slab edge detail as below. This treatment can also be adopted in addition to a ceiling if higher levels of sound insulation are sought, or to reduce noise ingress via spandrel panels.

Boxing in where no ceilings are proposed

The above list is not exhaustive and every project is different, however we hope it helps give you a flavour of the types of details to look out for. Sound insulation issues can have significant ramifications if not identified quickly and therefore should be considered early on in the design, particularly with regards to the setting out of mullions and transoms.

If you are working on a development with curtain walling and you are concerned about noise ingress or noise transfer we would be happy to help.

Noise barriers, or acoustic screens, are commonly used to reduce the effect of noise from roads, rail and industrial sources on residential properties. In particular, they are often required by local authorities to achieve recommended noise levels in external areas, including gardens and communal amenity spaces.

In order for noise barriers to be effective, they should achieve the following criteria:

• Barriers must be generally imperforate. Hit and miss fencing, slatted fencing or foliage are not effective noise barriers as sound passes through the gaps.
• Barriers should have a minimum mass of 10 kg/m2. Noise may pass through lighter weight materials.

For masses above 10kg/m2, the sound reduction provided by a noise barrier is unlikely to improve. The performance will be limited by sound diffraction over the top of the barrier. Therefore, a 10kg/m2 close-boarded timber fence will normally provide the same noise reduction as a 100mm concrete wall. Be careful if suppliers are recommending heavier noise barrier options for acoustic reasons, as these reasons may be false. Call us for an impartial view.

Set out below are common architectural screening options with comments on their acoustic effectiveness. It should be noted that, although some options will provide limited reduction in actual sound levels, any sort of visual screening has been shown to provide a subjective acoustic benefit – people are less bothered by a noise source that they cannot see!

Combinations of different barrier types are often also used for aesthetic or practical reasons. For example, an acoustic fence could be used on top of an earth bund where there was a requirement for a very high barrier (this is a particularly cost-effective option for sites where there is a lot of earth spoil which would otherwise have to be transported off site), or a green screen could be used in front of a brick wall for a more attractive aesthetic.

Cass Allen are experienced in the design and specification of noise barriers. Please let us know if you would like more information.

This month we were kindly invited to Paragon Interiors Group’s annual golf day at The Nottinghamshire Golf and Country Club and we thought it would be a bit of fun to run a competition to find out who could hit their ball the loudest.

A sound level meter was set up on the course to measure the maximum noise level during competitors’ drives at a distance of approximately 1m.

It was a very wet day, but despite the rain, there was no shortage of competitors to take on the challenge. Some interesting tactics were employed, with golfers selecting specific clubs and balls to try and make the loudest sound possible.

The worthy winner of the competition was Sam Wynn from Pulse Associates with a drive measuring a whopping 108 dBA. For reference, 108 dBA is about the same noise level you would hear during a sonic boom. Sam won himself a nice pair of Sony Wireless Headphones.

The full results of the measurements are shown below. There was a large variation in the measured levels with an average of around 97 dBA.

We found that the type of club and the strength of the shot were big factors in the measured noise level. The highest measured levels tended to also be very clean, powerful shots, although a few mishits also recorded very high levels!

Think you can hit a louder shot? Let us know when your next corporate golf day is and we will happily come along to find out!

The guide is aimed at developers and architects and sets out common reverberation control treatment options for rooms.

These treatments are used to prevent excessive reverberation and are often required to achieve acoustic specifications or regulations. In particular, reverberation treatments are required for the following development types:

• corridors in residential developments to comply with Building Regulations Part E
• teaching rooms in schools to comply with BB93 (as required by Building Regulations Part E)
• rooms within medical or healthcare facilities to comply with HTM08-01
• office workspaces (particularly open-plan workspaces) to achieve good quality work environments

The amount and type of treatment will vary depending on the size and use of the room. In many cases, the location of the material is also very important.

The performance of acoustic treatments is graded based on the amount of sound they absorb. The best absorbers are Class A (almost total absorption), however, Class B & C absorbers are also very effective.

Set out below are a number of common treatments along with their pros and cons.

Other treatments

As shown above, there are various treatment types, many of which also come in different styles and configurations. The key is finding the right treatment (or combination of treatments) for every project. Cass Allen has extensive experience in the design and specification of reverberation treatments including numerous products and suppliers. Please let us know if you would like more information.

Reverberation is an aspect of building acoustics that affects us on a daily basis, often without us even realising.

Have you ever been in a restaurant and struggled to understand the person across the table when they talk? Have you ever sat at the back of a classroom or lecture and been unable been hear what the speaker was saying?

If so, these issues were likely caused by excessive reverberation, which is caused by sound reflecting off room surfaces.

The solution to reverberation problems is to add more acoustic absorption into the space. Acoustic absorption can be provided by general room finishes (carpets, curtains, ceilings) and specialist treatments, such as hanging baffles, wall panels, diffusers etc.

Particularly sensitive spaces, such as classrooms, must achieve certain reverberation performance criteria in order to comply with Building Regulations. However, many spaces, such as such as atria, restaurants, shopping centres, swimming pools, etc, are not subject to regulations and can often be overlooked. Excessive reverberation in these spaces can lead to environments that are loud and uncomfortable to be in.

In these cases, appropriate reverberation design is recommended to ensure that the spaces are fit for purpose. Detailed reverberation modelling is a useful for tool for carrying out these assessments and helping specify appropriate treatment.

Below is an example of reverberation modelling which we carried out to help inform the design of the foyer of a luxury residential development. The floor (marble), walls and ceiling (plasterboard) were highly acoustically reflective.

These videos show graphically how the sound was predicted to disperse around the space. Colours show the propagation of sound pressure across the room from a loudspeaker positioned at A0.

The modelling software can also be used to produce ‘auralisations’, which allow clients and architects to listen to how the space will sound in advance. These auralisations are a useful tool in subjectively assessing the benefit and costs of treatments.

The following auralisations are of the above foyer with and without treatment:

Before:

After:

In summary, reverberation is an important consideration in the design of high quality development and we have the tools to help make sure that designs will be fit for purpose. If you have a project where reverberation may be an issue then please get in touch and we will be delighted to help.