Reverberation

When designing and constructing dwellings, builders are now responsible for making sure that all sound reverberation within common areas such as corridors and stairwells are reduced in line with Section 7 of ADE to prevent more reverberation around the common parts than is reasonable. As the surfaces of internal floors and walls are normally very hard, sound reverberation was subsequently found to have a detrimental affect on adjoining spaces to corridors. ADE sets out to ensure that these issues are addressed early in the design of a new structure. This may involve the specification of carpets, curtains, and absorbent ceiling tiles to achieve this requirement. Regulations for schools are covered in further detail in Building Bulletin 93: The Acoustic Design of Schools.

Referring in particular to multi-occupancy apartment blocks, hotels, residential homes, hostels and B&B’s, this change to the regulation is intended to control reverberation in common spaces such as entrance halls, corridors, walkways and stairwells. It is important to note that in terms of acoustic behaviour, Building Regulations Part E has re-classified hotels on parity with apartment blocks and they are now designated as rooms for residential purposes rather than temporary accommodation. This means the same standards should be applied to hotel rooms as to homes.

Protection against sound transfer

This applies to the levels of airborne and impact sound that are permissible to transfer between walls and floors of adjoining dwellings in rooms that are defined for residential purposes: including hotels, hostels, boarding houses, residential homes and apartments. Whilst this is not a new stipulation, Part E outlines that standards in all buildings must be improved for airborne and impact sound insulation to 43 dB DnT,w+Ctr for airborne sound on floors and walls and 64 dB L’nT,w for impact sound on floors for conversions and 45 dB DnT,w+Ctr for airborne sound on floors and walls and 62 dB L’nT,w for impact sound on floors for new-build projects.

In every case, the builder is responsible for making sure the sound insulation meets the above requirements and has options in terms of meeting the specified standards. He can either, subject his new-build construction to a Pre-Completion Test (PCT) or he can develop the building using a Robust Construction which is identified as a tried and tested detail which if registered with Robust Details Ltd does not require PCT. All conversions are subject to PCT because it is impossible to adopt a Robust Construction whilst utilising parts of the existing structure because their composition and condition can vary which in turn can alter the acoustic performance.

Pre-Completion Testing (PCT

Pre-Completion Testing was enforced from 1 July 2003 for conversions and 1 July 2004 for new-build to ensure that dwellings are achieving the revised performance standards. They are sound tests, which must be carried out at the builders own expense, to satisfy Building Control that the construction is up to standard. The tests should preferably be carried out by a UKAS accredited company or a member of the Association of Noise Consultants registration scheme. ADE requires that one set of tests are carried out on 10% of each construction type or sub-group (one set of tests for every ten adjoining houses, flats or rooms for residential purposes). Building Control can require more tests if they are of the opinion that the layout is sufficiently unusual to be classified as another construction type.

It was originally proposed that PCT should be adopted for both new-build and conversion. However, after lobbying from the House Builders Federation other options were also considered. Because PCT would place significant financial and time demands on builders, and because of the limited number of acoustic consultants prepared to carry out this work, a further route to compliance is currently being trialled by the Office of the Deputy Prime Minister and this is known as Robust Details.

Robust Details

Building Regulations Part E states that: “Robust Details are high performance separating wall and floor constructions (with associated construction details) that are expected to be sufficiently reliable not to need the check provided by pre-completion testing.” A company, Robust Details Limited has been formed to endorse a number of standard constructions that perform to the levels required, and to monitor their installation.

The industry is now in the midst of a three-year trial and assessment period regarding Robust Details and, despite a variety of teething problems regarding continuity in the standards of installations, looks increasingly likely to adopt the system permanently in 2007. It is important to note that a Robust Detail approach can only be implemented on new constructions. Any existing building undergoing change of use is obliged to undergo Pre-Completion Testing. Also should any departure from the Robust Detail manual be found then PCT applies.

Thermal efficiency

Whilst the revision to Building Regulations Part E signal improvements in the insulation against airborne and impact sound, their introduction has brought about additional problems in relation to thermal efficiency. The conventional rule for reducing sound transmission is the mass law. This states simply that the greater the mass of the structure, the less sound will be transmitted through it. Therefore if all dwellings were constructed out of a continuous concrete mould, acoustic airborne insulation issues between dwellings would decline significantly.

However, the benefits of reducing sound transmission in this way are in direct contrast to Building Regulations Approved Document L, which deals with the increasing demand for energy conservation. The document requires the builder to substantiate the thermal efficiency of the structure.

Thermal characteristics of materials (under Approved Document L [ADL]) are mainly proportional to their density, composition or thickness. Whereas acoustic characteristics are influenced by material stiffness, density, isolation, thickness, size of room and even external ambient noise more commonly referred to as background noise. This creates a problem as the lighter and more thermally efficient the material a builder uses, the less acoustically efficient his structure could become. This has created confusion amongst builders who have found it seemingly impossible to meet both opposing regulations. ADL is in the process of being revised to reconcile these issues.

Meanwhile Proprietary Acoustic System manufacturers have recognised this dilemma for some time and are continually developing relatively light weight systems offering discontinuous constructions making it possible to improve sound insulation within lightweight construction such as timber frame. During the course of developing these products, they also need to embrace the issues of ease and timing of incorporation into the works. These issues are often influenced by a change in the program of works, for reasons such as fire in the case of the timber frame building that recently burnt down in Colindale. It is a natural consequence of this event that the authorities will question ways of improving the fire protection of future developments.

Icopal’s specialist acoustic flooring division Monarflex Acoustic Systems is but one of these well established proprietary manufacturers that will consider these investigations within their testing regime to recognise a possible need to change the timing or method incorporation of building acoustics.

As this new robust detail system matures so additional systems are recognised by Robust Details Ltd and acknowledged with further updates to the Robust Details manual.

For more information on any of these issues and to receive reliable acoustic advice visit:

United Kingdom Accreditation Service at www.ukas.org  

Robust Details Ltd at www.robustdetails.com

House builders Federation at www.hbf.co.uk

Proprietary Acoustic System Manufacturers Association www.PASM.org.uk  

Or contact a Proprietary Acoustic System manufacturer.

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