Noise is one of the causes which lead to a vast number of court cases here in Spain, specially to noise transmitted from one property to another. Noise between rooms within a home is better tolerated than noise produced by the neighbour.
A building must meet a number of regulations and sound insulation is one of them. One of the quality indicators, which society is becoming increasingly aware of, is acoustic comfort.
In this article I will describe, along with the most common deficiencies in sound insulation normally found in Spain, some recommendations for the prevention and reduction of direct transmission of airborne and impact noise.
Poor insulation causes:
Often are produced from appliances, TV, strident music, loud voices, etc. normally from the house next door or from the flat
above or below.
- Noise from installation and services areas such as: lifts, boilers, air conditioning installation, garage doors etc.
The most common causes are:
Failure due to insulate airborne and impact sound insulation from construction elements.
Errors produced during the execution of works and which generate acoustic links.
Transmissions of noise from air distribution ducts usually due to the high velocity of the air in the duct due to
inefficient calculation of the heating or cooling loads.
Lack of special insulation in services room such as lifts service rooms or air conditioning compartments.
Errors produced in the design of water pipes which produces noises due to an excessive speed of the water.
Structural transmission of noise due to the poor relationship between volume and wall surfaces within a commercial unit. A
long rectangular room or hall will produce a longer reverberation period than a hall with walls that are not parallel for instance.
How is sound transmitted?
To first understand how noise propagates, perhaps it would be a good idea to explain how sound works. Sound is a wave phenomenon and, therefore, it is defined by two concepts: Intensity and frequency.
The way to measure intensity is by decibel (dB) and the unit of frequency measurement is the Hertz (Hz) or cycles
The frequency of sound is defined by its spectrum, which includes the amplitudes associated with each frequency band.
The dB (A) is used for the assessment of noise in general, and can be defined as the compliance to summarize in a single index the effect of sound pressure and content of spectral noise on humans ears.
Sound insulation provided to a construction element is defined by the curve determined by the level of insulation in (dB) in each frequency bands. Also the rates have been set as a single value for the insulation of building systems that allow comparisons of more simplified form.
The main objective of a sound insulation is that the construction elements that form a unit prevent exceeding the recommended emission levels. It is important to know that between two housing units apart from direct sound propagation exist other ways of sound transmission.
The existing regulation acknowledge that when there are two adjacent elements with similar mass sound insulation noise can be reduced to 5 dB or less due to the influence of this adjacent elements, therefore it is recommended to design a sound insulation that may offer theoretically an insulation superior to 5 dB recommended by the regulations. It is highly recommended that all noise bridging shall be avoided. Also avoid the use of a continuous false ceiling between two different commercial units as sound travel like a water flood, if it is not contained within a vessel sound will propagate through the air. Partitioning walls should go from floor to ceiling dividing the two spaces vertically.
Another usual mistake found often on site is floating floors covering two different spaces that have no rigid vertical disconnections between them.
Acoustic bridges involve a drastic reduction in total noise insulation achieved, which can lead to subsequent complaints. In cases where sound insulation could be critical it is recommended that, acoustic testing is carried to the whole project and special attention should be given to these issues during site inspection of the works.
The more mass (weight) is provided to a wall the greater the insulation will be, but theoretically only 6 dB is obtained by doubling the mass of any element, so if you want to obtain an insulation greater than 45 dB it is advisable to choose a solutions of double walling.
Actual values of wall density must be specified in the project together with the actual wall thickness designed to avoid confusion between different qualities of walls. We do not obtain the same sound insulation from two similar 10,5cm solid brick wall as they may have two different densities, so apart from specifying the type of walling do state its actual density.
The insulation provided by any construction element must be known.
You can make a theoretical estimate based on past knowledge of that type of material and its mass surface, however, it is recommended to apply the suppliers standardized test results for airborne sound insulation, carried out in an accredited laboratory.