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A revised acoustic guidance document, currently out for consultation, simplifies previous guidance and should prove easier to follow. But some observers believe the document could bring about complications of its own.

The design challenge of a healthcare building is to create a place which is conducive to well-being and healing. For patients, visitors and staff, adequate levels of natural light and ventilation together with appropriate degrees of visual and acoustical privacy would appear to be essential ingredients for such an environment. Yet these objectives are often inherently contradictory, and although current guidance documents encourage such an approach, it is not always easy to achieve. Guidance for acoustics can be particularly onerous, and architects have developed ingenious ways of meeting the requirements, or simply politely ignoring them.

The revised acoustic guidance document, the Health Technical Memorandum (HTM) 08-01 (Nov 2006), currently out for consultation, simplifies the HTM 2045 - 180 pages of acoustic guidance split between four different documents - into a single 40page document. It is a common perception among the profession that the original HTM 2045 is 'way too stringent'. Adrian Popplewell of Arup Acoustics, one of the authors of HTM 08-01, explains that the current guidance, if followed literally, requires that the walls of a maternity ward be thicker than the walls of a cinema. HTM 08-01, unlike its predecessor, is a performance-based document which is intended to give designers more leeway. Yet, according to David Rowley of Nightingale Associates, the new guidance may create a new set of problems. Rowley's view is that it will result in 'a process which is much more complicated and time-consuming for designers than the existing HTM 2045, and the need for acoustic consultants on projects becoming the norm'.

Giles Oliver of Penoyre & Prasad explains that the majority of new healthcare buildings are located on constrained urban sites where the configuration of the building, the nature of the facades and the decision to go with either a sealed or a naturally ventilated building are often dictated by site conditions.

Frontage on a busy road - seen in the practice's recently completed Moorfields International Children's Eye Hospital or under a flight path at its Thelma Golding Health Centre in Hounslow - meant in both cases that a sealed building was the only option.

Yet even where natural ventilation is a viable alternative, windows often lead to unacceptable levels of street noise in internal spaces. Two recent projects illustrate different approaches to window design which allow natural ventilation without compromising acoustic standards.

At Green Wrythe Lane Primary Care Centre in Carshalton in Surrey, Penoyre & Prasad designed bespoke aluminium projecting windows which incorporate acoustic attenuators. Adam Cole, Penoyre & Prasad project architect, explains that 'the attenuation is achieved by a removable cassette fabricated from 2 x 150mm acoustic louvres back-to-back with an integrated insect mesh positioned over an opaque aluminium sliding unit.' The window unit also includes two conventional side-hung units, one which enables extra ventilation and the other which allows cleaning. The units reduce sound transmission by 23dB and provide 0.4m 2 for ventilation. Fixed horizontal cedar louvres are also incorporated into the units for solar shading.

The sound attenuation is so effective that staff initially believed that the windows were not open.

At the Kaleidoscope project in Lewisham, south-east London, van Heyningen and Haward opted for natural ventilation as the desirable design solution and developed another bespoke approach to window design to overcome the acoustic problem.

Project architect James Gallie explains that 'at the early stages of the design we considered various proprietary systems for naturally ventilating the consultation rooms without impact from traffic noise, but found that the ventable area required far exceeded anything available on the market. As a result, we explored with Arup a secondary glazing solution, with deected air paths and acoustic absorption in the window reveals. While not performing as well as an acoustic ventilator, this offered the best balance between ventilation, acoustics, daylight and useability.'

The secondary glazing deects the air path from one side of the window to the other, and incoming noise is reduced by bespoke perforated-MDF reveals at the sides of the window that are located between the two layers of glass. Arup Acoustics calculated that this would reduce incoming noise from the busy road by 1 or 2dB - enough to make a difference when carrying out sensitive consultations in a naturally ventilated environment.

Naturally ventilated buildings pose an additional acoustic challenge because there is no background noise of mechanical ventilation to mask room-to-room transmission of sound. At quiet times of day, acoustic privacy between rooms can be a problem.

David Rowley of Nightingale believes that the implication of new guidance will be increased reliance on site testing 'to verify that specified standards are achieved in practice'.

He also believes that a straightforward computer programme, perhaps available on the Web, may well be necessary to help designers deal with the increased complexity of the new guidance.

Another guidance document which dramatically impacts the design of healthcare buildings is Health Facilities Note 30, which establishes infection-control guidelines. If the guidance is followed to the letter, no timber or fabrics are permitted and the resulting environments can be extremely antiseptic. Penoyre & Prasad associate Mark Rowe explains that while these concerns may be appropriate for a hospital with acute care, they are less applicable to primary-care institutions, which are closer in nature to a community building than to a hospital. Gallie echoes this view, stressing the fact that new health facilities such as Kaleidoscope, where there is no acute care or invasive surgery, are more about providing comfortable spaces for family consultation and social care than about creating clinical environments.

Equally important is the role of these new health centres as civic buildings and focal points of community activity, an aspect beyond the reach of even the best guidance.

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