HOLY CROSS SIXTH FORM COLLEGE, BURY ACOUSTIC DESIGN DUTIES
Background
Holy Cross is a Catholic Sixth Form College and University Centre on Manchester Road in Bury, situated close to the busy and noisy Manchester Road. It regularly ranks as one of the top ten sixth forms in the country. To accommodate growing pupil rolls, it needed a new 3-storey teaching block and chapel.
Proposition
Miller Goodall was appointed to undertake acoustic design duties for the new facilities. The development required a BREEAM rating of Very Good, and in order to achieve the relevant acoustic credits, the acoustic performance requirements of Hea 13 and Pol 8 within BREEAM Education 2008 were targeted.
This required careful consideration of the impact of the design on acoustics to achieve the relevant criteria for indoor ambient noise levels, sound insulation between acoustically sensitive spaces and reverberation times in teaching rooms.
Investigation
In order to satisfy both the indoor noise level requirements of BB93 and the ventilation requirements of BB101 Ventilation of School Buildings, classrooms on the noisiest elevation were provided with secondary acoustic glazing and mechanically ventilated. The in situ airborne sound insulation of high performance moveable walls was maximised by careful detailing at junctions, including the provision of acoustic breaks in the floor slab beneath moveable walls to prevent flanking noise transmission. The selection of ceiling tiles with excellent sound insulation as well as acoustic absorption reduced the transmission of noise through the relatively thin floor slabs while achieving the required reverberation time criteria.
Acoustics within the chapel also needed careful consideration, as the client wanted a space that was not too ‘dry’ for choristers but also not overly ‘live’ so that speech intelligibility was adversely affected. In order to achieve this compromise, a combination of surface finishes with very different properties was utilised. Strong early reflections near the chancel were achieved with timber panelling to side walls to enhance speech intelligibility, while acoustic absorption to the underside of the mezzanine floor reduced unwanted reverberation. The use of quadratic diffusers on the rear walls helped scatter sound waves and prevent unwanted flutter echoes. Acoustically attenuated ‘wind catchers’ were utilised within the chapel to provide natural ventilation to the space, while also achieving low ambient noise criteria.
Action and outcome
On completion of the project, acoustic compliance testing demonstrated that project criteria had been achieved in the majority of spaces within the building, thereby allowing the BREEAM credits to be awarded.
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