BUILDING DESIGN USING COLD FORMED
STEEL SECTIONS: ACOUSTIC INSULATION

3. PERFORMANCE REQUIREMENTS

There are Building Regulation requirements for sound insulation between attached dwellings in the UK, but no mandatory requirements for other types of building such as hotels or schools, or for sound insulation within dwellings. There are, however, a number of authoritative documents which suggest performance standards; these are cited below in Sections 3.1 to 3.5.

3.1 Multiple dwellings

The Building Regulations applying to England and Wales, the Building Standards applying to Scotland and the Northern Ireland Building Regulations have broadly similar requirements for multiple dwellings. The following information is based on the Building Regulations for England and Wales.

The Regulations require that walls and floors between dwellings resist the transmission of sound. Approved Document E to the Building Regulations gives advice on achieving good sound insulation. The precise legal position is that if the advice in Document E is followed then this is evidence tending to show that the Regulations have been complied with. Document E includes a number of standard constructions and advice on their detailing. It also includes a test method which can be used to show that other types of construction have appropriate sound insulation. These tests must be carried out in accordance with BS 2750.

The requirements set out in Document E are given in terms of the single figure rating values DnT,w for airborne sound and L'nT,w for impact sound, and are summarised in Table 2.

Table 2: Permitted sound transmission values

The acoustic performance of external walls is largely dependent upon that of the windows and other elements in the external envelope. Neither the Building Regulations nor the NHBC Standards set out minimum performance standards; however, NHBC Specifications do require that flanking walls (usually external walls) should be designed to resist flanking sound transmission, and the Building Regulations have minimum mass requirements for certain flanking walls (see Section 3.3).

3.2 Individual dwellings

The Building Regulation sound insulation requirements do not apply to individual dwellings, i.e. dwellings which do not share floors or walls with other dwellings. However, occupiers do expect a certain level of acoustic privacy between rooms. The only specific numerical requirements for sound insulation within the same dwelling are those given in the technical manuals of the National House Building Council and Municipal Mutual Insurance which apply to dwellings which carry their respective insurance guarantees. The Municipal Mutual manual requires that partitions and floors which separate a WC from another part of a dwelling should be insulated to provide a weighted sound reduction R of not less that 38 dB when tested over a frequency range of 100 Hz to 3150 Hz in accordance with BS 2750. The NHBC requirements are similar.

Most dwellings are constructed with internal partitions and internal floors capable of giving a weighted sound reduction R of 35 dB. Internal floors will give an L'nT,w rating of 80 dB or more with no covering. However, soft floor coverings like carpets will improve this performance considerably, probably to an L'nT,w of less than 60 dB. Although there is anecdotal evidence to suggest that some purchasers would be prepared to pay for higher standards, internal sound insulation does not seem to be a major factor influencing house purchase and therefore the levels of insulation mentioned above are probably satisfactory to most people. In practice, the actual sound insulation obtainable between rooms will also depend on the room layout, position and type of doors, etc.

3.3 Offices

The general trend at present in commercial design is for large open plan areas with private offices for managers at the perimeter. Private offices are generally created by the use of demountable partitioning systems.

The sound insulation of partitions is usually specified by manufacturers in terms of the sound insulation they can achieve in a laboratory test, independent of any flanking transmission which occurs in real buildings. Building specifications however often express the sound insulation that is required in terms of the office-to-office sound insulation, i.e. including flanking transmission, for which BS 8233: 1987 recommends values. The Standard suggests a minimum sound insulation between offices of 35 dB, and a minimum average sound insulation of 45 dB where privacy is required. Other research, for example Parkin et al, has suggested criteria in terms of the sound insulation between offices and the existing background sound levels. For typical background sound levels in offices, Parkin's recommendations are similar to those of BS 8233: 1987.

Sound insulation values in excess of 40 dB, for the average of the sixteen measurements taken between 100 Hz and 3150 Hz, are difficult to achieve using conventional demountable partition systems, and the detailing of these is often complicated by the presence of computer floors and suspended ceilings which can compromise acoustic performance.

3.4 Other buildings

Authoritative advice on sound insulation for other types of building is given in BS 8233: 1987.

Rooms in educational buildings, are categorised into four types. Sound insulation requirements are set down using single figure values. A summary of the requirements is given below.

Table 3: Minimum average airborne sound insulation

Note: where a room is likely to have a dual use, e.g., a dining room to be used as a classroom, the higher sound reduction value should be used.

From Table 3 it can be seen that the minimum average airborne sound insulation values suggested by BS 8233 range from 25 dB to 45 dB. The Standard also recommends that in multi-storey buildings the minimum requirement for impact sound insulation of floors above teaching spaces should be equal to a standardised weighted impact sound pressure level L'nT,w of 70 dB. A number of other specific detailed recommendations for educational buildings are made in BS 8233 covering particular situations.

BS 8233 recommends that hotels and hostels should have partitions, and floors between rooms and corridors, with an average sound insulation over the range 100 Hz to 3150 Hz (D average) of not less than 45 dB.

The standard also recommends that a sound insulation approaching that required for flats is desirable where there is a likelihood that audio equipment will be used at high volume.

No sound insulation requirements are given for other buildings, although the standard does discuss certain qualitative aspects of the acoustic performance necessary for health and welfare bui16ings, computer installations, museums and art galleries, libraries and auditoria, law courts and council chambers, religious buildings, indoor sports centres and swimming pools and sports grounds and stadia.

3.5 Summary of criteria

The performance requirements for different types of building are summarized in Table 4.

Table 4 Summary of minimum sound insulation requirements