Building Fabric 04 – Sound Insulation

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As we have considered in a previous article, sound can have an impact on our physical and mental well being. Surveys have indicated that 50% of people find their home in some way unsatisfactory because of noise intrusion – this includes people living in new homes built to modern building standards. It is an important consideration when designing buildings that we consider the sound quality of our built environment. Unwanted sound is perceived as a nuisance and can cause a number of emotional effects.

 

The primary noise intrusion is outside noises, particularly traffic both in permanent noise levels (a busy road), and short term, (passing airplane, train etc). Outside noise levels can influence levels of concentration, work performance and interrupt our rest or sleep.

 

A factor to consider when designing ventilation strategies is the opening of windows in warm temperatures and whether this activity will be impacted by external noise levels. Reports indicate that occupants are more willing to accept higher levels of noise from outside for the sake of natural ventilation through windows on a warm day.

 

Other noise sources can include industrial noise, construction noise and noise from leisure and entertaining. Inside buildings we can experience noise issues from other occupants, machinery and appliances and so on. It is also worth noting some activities require specialist sound design, for example recording studios.

 

Noise can have many different impacts on peoples lives, including:

  • Hearing loss
  • Quality of life
  • Interference
  • Distraction
  • Expense

Noise

There are three main action areas when considering noise in a building.

 

Source – this may be from outside a building such as traffic noise, or within the building such as occupant noise

Path – the sound path may be from outside of the building or within the building

Receiver – the receiver of the sound may be the complete building, a room of the building or it could be the person that is hearing the sound 

 

Noise Transfer

Noise can be transferred to a building or between rooms in different ways, depending on the type of sound. There are two main types of sound:

 

Airborne Sound

Airborne sound travels through the air before reaching a partition. This could be described as voices, radio, music, traffic noise and so on. These sounds travel through the air before reaching the building assembly, or partition.

 

Sound type airborne

Impact Sound

Impact sound is generated on a partition or building assembly. This could be described as footsteps, windows or doors slamming, vibrating machinery and so on. This type of sound will usually travel through the air to reach your ear but its source tends to be on the structure itself. 

 

Sound type impact

Controlling airborne and impact sounds often require different approaches, these can be described as sound insulation and sound absorption. Sound insulation looks at reducing the amount of sound energy that is transmitted to an adjoining airspace. Sound absorption reduces the sound energy reflected by the surfaces within a room. 

 

Generally speaking, sound absorption has an affect on the quality of sound, rather than reducing the noise itself. 

Sound Insulation

 

Insulation helps to control the transmission of both airborne and impact sound. It is measured using the sound reduction index (R), which is the measure of the insulation against the direct transmission of airborne sound. The index is measured at different frequency bands as insulation varies with frequency. 

 

The following table looks at some common construction materials with their sound reduction indices measured at different frequencies. The higher the sound reduction (R) value, the better the material at reducing the transmission of sound. 

 

Sound Insulation -Sound reduction index

Ensuring good sound insulation

 

When designing for sound insulation it is important to ensure airtightness and uniformity in the insulation. Air gaps will have an impact on overall performance. An example of this, if a brick wall contains a crack or hole that represents only 0.1% of the total area of the wall, the average SRI of the wall is reduced from 50dB to 30dB (McMullan).

 

Air gaps can be a particular problem around windows and doors, seals around partitions, joins with floors, ceilings, service pipes and so on. 

 

It is also good to consider isolation, or discontinuous construction, which will help with the reduction of sound transmission. A good example of this would be the cavity in a window, floating floors, and resilient mountings used for vibrating equipment. 

Working with Sound Insulation Regulations

 

Regulations for sound insulation tend to be most important in walls and floors shared between dwellings, for example flats or joined houses. There are also specific requirements for buildings such as hotels, student housing, schools, nursing accommodation where sound insulation between rooms and corridors needs to be considered carefully. 

 

Generally speaking, the areas where sound insulation must be considered in order to comply with regulations are:

The building envelope – all elements that separate the dwelling from external noises such as road, traffic, trains and industry.

Separating walls – all walls that are between dwellings and within the same dwelling

Separating floors – all floors between dwellings

 

The Building Regulations require a minimum level of sound insulation for the building envelope and internal walls and floors, protecting from either airborne sound or impact sound, or both. The following diagram demonstrates the different requirements for a simple set of flats. 

 

Sound insulation requirements in flats

Walls tend to require insulation against airborne sound, while floors tend to require insulation from both airborne and impact sound. 

 

The following table demonstrates the sound insulation standards required for separating walls and floors in houses and flats.

 

The following details are examples of guidance provided in the building regulations document part E, demonstrating examples of what is considered to be acceptable construction standards for sound insulation.

 
 
 

A great resource that provides detailed information and diagrams for many types of construction is the Robust Details Handbook. The book contains separating wall and floor construction details that comply with Part E of the building regulations “resistance to the passage of sound”. The use of the scheme provides an alternative to pre completion testing for demonstrating compliance. The handbook can be downloaded from the Robust Details website. (http://www.robustdetails.com)

 

The details cover timber frame, masonry and steel frame construction – some examples follow:

 

Resources

Robust Details – http://www.robustdetails.com
Building Regulations in Brief – Ray Tricker & Samantha Alford
Environmental Science in Building – Randall McMullan

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