This section of the RIA further explains the nature of the main changes associated with the new Requirements E1 to E3 and the guidance in Approved Document E.
(i) Changes resulting from the extended scope of Requirement E1
26. The scope of the current Part E is restricted to sound transmission between dwellings, and between dwellings and other buildings, but no definition of 'dwelling' is provided. A working definition of dwelling is in common use that restricts the current application to a self-contained living space containing its own cooking, washing and sanitary facilities.
27. The Performance Statement in the current Approved Document E states that:
"In the Secretary of State's view the requirements of E1, E2 and E3 will be met if the relevant parts of the dwelling are designed and built in such a way that noise from normal domestic activities in an adjoining dwelling or other building is kept down to a level that will not threaten the health of the occupants of the dwelling and will allow them to sleep, rest and engage in normal domestic activities in satisfactory conditions."
This current performance statement suggests that the requirement should apply to the spaces in any type of building which cater for the domestic functions listed. This would include not only dwelling-houses and flats, but also hotels, hostels, student accommodation, nurses' homes and elderly persons' homes. The explicit extension in the scope of Regulation E1 to include rooms for residential purposes will ensure that the intention of the Requirement is made clear.
28. The drafting of Requirement E1 also extends the scope of the current Requirement to ensure that reasonable resistance to sound is provided when walls and floors separate a bathroom from other parts of the same building, such as when a bathroom adjoins a common circulation space in a block of flats.
(ii) Measures to improve sound insulation
29. This group of changes introduces an explicit minimum performance standard and uses a new rating method for airborne sound insulation that places greater emphasis on low frequencies and corresponds better with subjective evaluations of sound insulation. It is not possible to make simple comparisons between the airborne sound insulation standards and the limits for inclusion of constructions in the current guidance because of the nature of the new rating method and the allowance made for measurement uncertainty in the pre-completion testing regime15.
30. In very general terms, for both new dwellings and material change of use (as defined in Regulation 5 of the Building Regulations), the required airborne sound insulation for separating walls has been increased by at least 3 dB and that for separating floors has been increased by at least 4 dB (n. b. the opportunity has also been taken for a small additional improvement in the performance standard for separating floors to bring it into line with the standard for separating walls). The required standard for resistance to the transmission of impact sound for new dwellings has been improved by 5 dB. On the basis that 3 dB is probably the smallest discernible change in performance, standards need to be raised by at least this amount for the change to be significant. The standards are generally in line with improved standards currently being adopted by some developers and bring our approach more into line with other parts of Europe.
31. For material change of use the required minimum airborne and impact sound insulation performance has been set at a level that is 2 dB lower than that required for new build in recognition of the difficulties of controlling flanking transmission in some circumstances. The resulting increase in the required standard is therefore broadly in line with the increase in required standard for new build16.
(iii) Measures that improve compliance with Requirement E1
32. This group of changes seeks to stimulate greater compliance with the required standards of sound insulation through the introduction of a pre-completion testing regime the cost of which is to be borne by the developer. The regime is accompanied by the removal of Sections 3, 4 and 6 of the current Approved Document, which describe alternative methods for meeting the current Requirements. In future, there will be no restriction on the use of other types of building construction provided that the required standards are met when the properties are tested. Therefore, in the longer term, given a high rate of compliance with the required standards, the regime will promote greater freedom for the industry and enable a more de-regulatory approach to be taken.
33. The pre-completion testing regime does not require 100% testing of all new attached residential properties and is based on testing a sample of new properties selected at the discretion of the building control body following the guidance in Section 1 of the Approved Document. The requirement on a developer to improve the sound insulation when failures are detected is crucial to the system and is seen as being the main stimulus to the general achievement of the minimum performance requirements through the adoption of improved quality control procedures on site. Constructions included in the revised Approved Document E should meet the required standards provided that there is sufficient attention to detail and that a good standard of workmanship is maintained.
34. It may be difficult to meet the required standards when dwellings are created as a result of the material change of use of some historic buildings. The conversion of such buildings to residential use presents particular challenges and once all reasonable remedial work has been undertaken, a system of 'test and declare' is to be used. The intention of this system is to strike a balance between the demand for this type of property, the need to conserve the special characteristics of some historic buildings and the rights of occupants to know the standard of sound insulation in the conversion. In general, it is often difficult to estimate the likely performance of dwellings created as a result of material change of use and, for this reason, the pre-completion testing regime encourages more frequent testing of conversions.
35. Changes are also made to the structure and content of Approved Document E. These changes are in response to feedback from users, changes in construction good practice and complaints from building occupants. Some of the changes are necessary to bring the Approved Document into line with revisions of British and European Standards. All these changes should also contribute to improved compliance with the Requirements
36. Requirement E2(a) incorporates and extends a current requirement for the sound insulation of internal walls made by the NHBC (National House Building Council)17 and will extend and standardise current good practice. The requirement seeks to reduce disturbance for people in rooms designated as bedrooms and to protect the privacy of people using toilet facilities.
37. Requirement E2(b) extends the same principle to improve the sound insulation of all internal floors.
38. Reverberation describes how long sound takes to die away after the source has stopped. By paying attention to the control of reverberation in the common internal parts of blocks of flats and buildings containing rooms for residential purposes it is possible to prevent excessive build up of sound in corridors, stairwells and hallways and so reduce the noise transmitted to adjoining residential rooms.
39. The guidance has been provided in terms of the amount of absorption required rather than a target reverberation time. This overcomes the practical difficulties of determining compliance with a target reverberation time in awkwardly shaped spaces.
40. Although this RIA reviews the need for each of the changes on an individual basis it is important to appreciate that Requirements E1 - E3 will act together to change the noise environment in buildings. For example, if steps are taken to improve the sound insulation between dwellings then occupants may notice noise sources within a dwelling more readily. Providing additional absorption in the common parts of blocks of flats will help to improve insulation between flats as well as prevent build up of noise in the common parts. The guidance has been drafted to take into account the interactions between the various issues.
15 For example, inclusion of a particular new build wall construction in the current guidance is based on the following limits:
i. The mean value of individual airborne sound insulation tests on a number of specimens was at least
52 dB (DnT,w).
ii. The ‘true’ performance of each of the test specimens was at least 49 dB (DnT,w). The true performance of an individual wall is a notional quantity, corresponding to the mean value of a large number of tests carried out on it.
In the revised guidance the intention is that the ‘true’ performance of all individual walls should meet an improved minimum standard, with the consequence that the average ‘true’ performance will be in excess of this standard.
i. For masonry walls and concrete floors the new rating method generates values for airborne sound insulation that are generally about 5 dB lower than the current method.
ii. The nearest equivalent to the 49 dB standard would therefore be 44 dB using the new DnT,w + Ctr rating.
iii. The standard has then been raised by 3 dB and a 2 dB allowance made for measurement uncertainty as part of the pre-completion testing regime, to give the new minimum standard of 45 dB (DnT,w + Ctr).
16 On the assumption that the ‘true’ performance of a remedial treatment included in the current guidance would be 2 dB lower than the mean performance given in current Section 6.
17 NHBC Standards – Chapter 6.3-D9, September 1999 edition
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