Airborne sound
With airborne sound, the problem of insulation is almost entirely one of reflecting energy back into the source room and therefore a function of surface density.
Obviously the results of using different materials vary according to the type of building construction and the type of floor. Reduction in the size of floor area and increase in the mass of the supporting walls will reduce transmitted airborne noise, as will the rigidity of construction between the floor and supporting walls.
Impact sound
Unlike airborne sound, the performance in respect of insulating against impact sound is not so dependent on the density of the floor support construction, but rather a combination of floor density and the resilient nature of the floorcovering applied to it. Test results show that increases in density of the floor construction only marginally affect insulation against impact transmitted sound, while the application of floor coverings such as a floating wood floor, of suitable resilience and thickness, will have dramatic results. Engineered wood, for instance, having a relatively resilient core material, is a relatively good absorber of impact noise.
Meeting regulations
The regulations governing sound transmission levels in new buildings consider sound generated in two different ways. A source such as a television, radio or hi-fi system will produce sound waves in air that, in turn, produce vibrations in party walls, ceiling, doors, windows and the floor. Alternatively, a wall or floor separating two dwellings may be excited by the direct impact of a solid object, for example, footsteps, dropped objects, etc.
Only party floors are required to meet a prescribed standard of impact insulation, but both party walls and party floors are required to provide a standard amount of insulation against airborne sound. In compliance with the Building Regulations, any adverse deviation in values in respect of either airborne or impact sound resistance must not exceed the stated values.
For refurbishment projects, Building Regulation's Document E (and its revised form) includes strict guidelines for minimising the transmission of sound and impact noise between floor levels. While there are specialised sound insulation systems available (shock and sound absorbent batten mountings, underlayments, etc.) the type of wood floor and the method of installation used plays a major role in reducing any transmitted noise.
The floating floor method of installation ensures the floor can be sound insulated from both the sub-floor and walls. Quite simply, the floor is assembled and installed as a raft and is free to expand and contract without touching the perimeter walls or any other solid objects that may transmit sound, such as pipework, support columns and door frames, etc.
Minimum standards
The Building Regulations 1991, Document E, for refurbishment work lays down minimum standards for performance of 48dB reduction, or more, for airborne noise, and 65dB reduction, or less, for impact noise. With the introduction of revised standards there is also a requirement to demonstrate that the installation can meet these requirements.
The recent DETR proposals for amending Part E of the Building Regulations 2000 are expected to have a dramatic effect on the role of the flooring specifier and contractor. Not the least of the new measures is the move towards onsite testing of sound insulation prior to fitting out. Carried out at the developer's expense, the testing is thorough, comprising multiple tests for both airborne and impact noise. If any airborne or impact sound insulation test result is more than 3dB from the required standard, remedial work must be carried out and a positive re-test performed to satisfy the regulations.
Such measures will, and already have, spurred the development and introduction of more effective specialised flooring systems to combat sound and impact noise transmission.
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