Introduction
Sound is a form of energy that can be transmitted from source and travel through a medium (e.g. air, timber). Typically, in construction sound is transmitted through construction elements such as walls and floors. The sound is usually created either by impact against one of the construction elements or from an airborne source. In each case, the sound can be transmitted directly or indirectly.
It is important to ensure that dwellings achieve a reasonable level of insulation of sound coming from adjoining dwellings or other parts within the same dwelling.
The main method of sound reduction/insulation is to prevent or disrupt the transmittal of the sound from its source to the receiver. This can be achieved by:
Using construction materials with a high density that will not vibrate as easily to create a barrier.
Installing sound insulation to close any gaps where sound might be able to travel through.
In practice the most effective method of sound insulation is the application of a combination of the above methods.
The guidance provided in this document relates to methods in which reasonable levels of sound insulation can be achieved by dwellings adjoining other buildings and buildings that comprise one or more dwellings with respect to non-complex standard design and construction.
While this document provides guidance on how to best reduce unwanted sound transmission it does not guarantee that the transmission of all unwanted sound will be eliminated.
Diagram HE1 - Scope of requirement of Regulation E1 - Extract from TGD E
Definitions
Absorption - Conversion of sound energy to heat, often by the use of a porous material.
Absorption coefficient - A quantity characterising the effectiveness of a sound absorbing surface. The proportion of sound energy absorbed is given as a number between zero (for a fully reflective surface) and one (for a fully absorptive surface).
NOTE: Sound absorption coefficients determined from laboratory measurements may have values slightly larger than one. Refer to I.S. EN ISO 354.
Absorptive material - Material that absorbs sound energy.
Airborne sound - Sound which is propagated from a noise source through the medium of air, e.g. speech and sound from a television.
Airborne sound insulation - Sound insulation that reduces transmission of airborne sound between buildings or parts of buildings.
Air path - A direct or indirect air passage from one side of a structure to the other.
Cavity stop - A proprietary product or material such as mineral wool used to close the gap in a cavity wall to minimise flanking sound transmission along the wall cavity.
Cavity barrier - A construction provided to close a concealed space against penetration of smoke or flame or provided to restrict the movement of smoke or flame within such a space (refer to TGD B – Fire Safety).
Decibel (dB) - The unit used for many acoustic quantities to indicate the level with respect to a reference level.
Density - Mass per unit volume, expressed in kilograms per cubic metre (kg/m3 ).
Direct transmission - Refers to the path of either airborne or impact sound through elements of construction.
DnT - The difference in sound level between a pair of rooms, in a stated frequency band, corrected for the reverberation time. Refer to I.S. EN ISO 16283-1.
DnT,w - The weighted standardised level difference. A single number quantity (weighted) which characterises the airborne sound insulation between rooms in accordance with I.S. EN ISO 717-1.
Dynamic stiffness - A parameter used to describe the ability of a resilient material or wall tie to transmit vibration. Specimens with high dynamic stiffness (dynamically ‘stiff’) transmit more vibration than specimens with low dynamic stiffness (dynamically ‘soft’). Refer to I.S. EN 29052-1 for resilient materials. See BRE Information Paper IP 3/01 for wall ties.
Flanking element - Any building element that contributes to sound transmission between rooms in a building that is not a separating floor or separating wall.
Flanking transmission - Sound transmitted between rooms via flanking elements instead of directly through separating elements or along any path other than a direct path.
Floating floor - A floating floor consists of a floating layer and resilient layer (see also floating layer and resilient layer).
Floating layer - A surface layer that rests on a resilient layer and is isolated from the base floor and the surrounding walls (see also resilient layer).
Frequency - The number of pressure variations (or cycles) per second that gives a sound its distinctive tone. The unit of frequency is the Hertz (Hz).
Frequency band - A continuous range of frequencies between stated upper and lower limits (see also octave band and one-third octave band).
Hertz (Hz) - The unit of frequency of a sound (cycles per second). Impact sound - Sound resulting from direct impact on a building element.
Impact sound insulation - Sound insulation which reduces impact sound transmission from direct impacts such as footsteps on a building element.
Internal floor - Any intermediate floor within a dwelling. Intermediate landing - A landing between two floors (see also landing).
Internal wall - Any wall within a dwelling that does not have a separating function.
Isolation - The absence of rigid connections between two or more parts of a structure.
Landing - A platform or part of a floor structure at the top or bottom of a flight of stairs or ramp.
L’nT - The impact sound pressure level in a stated frequency band, corrected for the reverberation time. See I.S. EN ISO 140-71.
L’nT,w - The weighted standardised impact sound pressure level. A single-number quantity (weighted) to characterise the impact sound insulation of floors, in accordance with I.S. EN ISO 717-2.
Mass per unit area - An expression in terms of kilograms per square metre (kg/m2 ).
Noise - Unwanted sound.
Octave band - A frequency band in which the upper limit of the band is twice the frequency of the lower limit.
One - third octave band - A frequency band in which the upper limit of the band is 21/3 times the frequency of the lower limit.
Rw - A single number quantity (weighted) which characterises the airborne sound insulation of a building element from measurements undertaken in a laboratory, in accordance with I.S. EN ISO 717-1.
Resilient layer - A layer that isolates a floating layer from a base.
Resilient material - A material which returns to its original thickness after it has been compressed.
Resonance – increased amplitude of oscillation of an object when it is subjected to vibration from another source at or near its own natural frequency.
Reverberation - The persistence of sound in a space after a sound source has been stopped.
Reverberation time - The time, in seconds, taken for the sound to decay by 60 dB after a sound source has been stopped.
Separating floor - A floor that separates a dwelling from an adjoining dwelling or another part of the same building.
Separating wall - A wall that separates a dwelling from an adjoining dwelling, another part of the same building or from an adjoining building.
Sound pressure level - A quantity related to the physical intensity of a sound.
Sound reduction index (R) - A quantity, measured in a laboratory, which characterises the sound insulating properties of a material or building element in a stated frequency band. Refer to I.S. EN ISO 10140- 1 to 5.
Spectrum - The composition of a particular sound in terms of separate frequency bands. Structure-borne sound - Sound which is carried via the structure of a building.
∆Lw - The measured improvement of impact sound insulation resulting from the installation of a floor covering or floating floor on a test floor in a laboratory (See I.S. EN ISO 717-2).
Direct Sound Transmission
Direct sound transmission is sound transmitted directly via the construction element i.e. wall or floor. The level of airborne sound transmitted through solid masonry construction is dependant on the mass of the wall. While the mass of the wall is the main factor in reducing the sound transmitted in masonry walls the stiffness and damping also play an important part.
Floors should be constructed to limit the passage of airborne sound and in the case of floors separating dwellings from one another they should also limit to passage of impact sound.
Impact noise is caused when a source of vibration comes in direct contact with the building element, the structural vibration is transmitted from the point of impact through the structure causing it to vibrate and radiate the sound. The level of impact noise heard below a floor depends on a number of factors including the force of the impact, the floor construction (the vibration characteristics of elements) and floor coverings.
Where soils floors are used the passage of sound is reduced depending on the mass of the element. If a floating floor is provided a resilient layer is installed to separate the walking surface from the base of the floor – this will reduce both impact and airborne sound transmission.
It is important to ensure any resilient layer to be installed in not too stiff and it is also important to ensure that the installation of a resilient layer is not negated by the presence of rigid bridges such as fixings and pipes that would transmit the sound.
It is important to ensure that all joints and porous materials are appropriately sealed within the structure to limit the air paths available for sound.
Flanking transmission of Sound
Flanking transmission is the transmission of sound indirectly from one side of a building element to the other i.e. wall/floor. This form of transmission of sound occurs when there is a path which sound can travel along between elements on opposites of a wall or floor, this may be via an air space or a continuous solid structure.
While the junctions of a flanking element and a sound resisting element provide resistance to structural waves it may not be sufficient unless the flanking element is heavy or is divided by windows or other similar openings in small sections that will not readily vibrate.
In general, there is a minimum mass required for panels connected by paths through air spaces i.e. ceilings connected by air in roof spaces and over the ridge in of separating walls. Should this path be blocked by a non-porous material then the minimum required mass may be reduced.
Design Considerations
While construction materials and workmanship have a significant impact on the reduction of sound transmission throughout buildings another important consideration is the layout of the dwelling.
At the design stage it is important to consider the layout of the dwelling ensuring in so far as is possible that rooms where noise generation would be high are located away from noise sensitive rooms i.e. kitchen/living are not beside bedrooms.
Room layout and building services
Internal noise levels are affected by room layout. The layout should be considered at the design stage to avoid
placing noise sensitive rooms next to rooms in which noise is generated where possible.
Diagram HE2 - Principle of sound transmission paths - Extract from TGD E
