DESIGN PROCESS
TECHNICAL EVALUATIONS
decibels by which sound reduces as it passes through the system. The figure will depend on the frequency of the sound in the source room, so measurements are generally taken across a range of frequencies between 50Hz and 5,000Hz and are taken at one third octaves. Test results are then compared with a standardised reference curve to produce a weighted sound reduction index ( R w ), where figures across a range of frequencies between 100Hz and 3,150Hz are used in accordance with BS EN ISO 717-1 The National Building Regulations do not require any specific requirements for the sound insulation performance of external walls. When a significant external noise source is present – for example, a building is being constructed near a railway line, road or airport – only then is the acoustic performance of an external wall considered. The acoustic performance of the external façade will be controlled by the level of prevailing ambient noise. The windows and any trickle vents will often be the dominant source of noise ingress into a building. There are separate guidance documents depending on the building type, as listed below: Healthcare NHS Estates Health Technical Memorandum HTM 2045
Technical evaluations may be required when considering the fire performance of the interfaces of the through-wall system with the structure or other construction products/systems not covered in the initial test reports. Assessments and technical evaluations (sometimes referred to as engineering judgements) are still widely carried out and there are several areas where they remain an important part of the construction process. Extended application standards (EXAPs) give a clear interpretation of which scenarios can be claimed using testing as a basis for justification. The rules are published within the test or EXAP standard. These standards and the rules within are reviewed and updated through well documented BSI/CEN committees. The second route is a less formal technical evaluation. ASFP Advisory Note 17 gives more detail of situations where assessments and technical evaluations can be used, and where an evaluation would be inappropriate. The assessment should be carried out in accordance with the PFPF’s Guide to undertaking technical assessments of fire performance of construction products based on fire test evidence.
Education DfES Building Bulletin 93 (BB93)
ACOUSTIC PERFORMANCE
Office buildings – British Council of Offices or BS 8233 Guidance on sound insulation and noise reduction for buildings Commercial, retail and leisure buildings BS 8233. Sound insulation and noise reduction for buildings - Code of Practice Industrial BS 8233 and BS 4142 Method for rating industrial noise affecting mixed residential and industrial areas Residential and hotels Approved Document E (2003 Edition) of the Building Regulations 2000
SOUND INSULATION Sound insulation is achieved by reducing the amount of sound energy that passes between two spaces separated by a dividing element. Airborne sound insulation is achieved where spaces are separated with products containing mass as well as soft absorbing products and installed so that they are airtight to reduce flanking sound paths through gaps. The system owner should be consulted to reduce flanking paths between residences. The sound insulation of a system such as through- wall can be tested in a laboratory to produce a single-figure rating reflecting the number of
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