Quiet at the back please

The Bexley Business Academy would not look out of place in a modern business park. Large glass facades and banks of steel louvres give the building a crisp, high-tech feel that is light years away from the hotchpotch of tatty outbuildings that typify British schools. The office theme continues inside. There are large open-plan spaces, a boardroom, a spacious restaurant, and information and communications technology that would be the envy of brokers and bankers in nearby Canary Wharf.

As well as being the first business-sponsored government academy, it will also be the first school in the country to provide a cradle-to-university service (it will take children from infancy to 18 years old) with a crèche, a nursery, a primary school and a secondary school.

World-renowned architect Foster and Partners provided the designs for Bexley Business Academy, but not the inspiration. That accolade goes to educationalist and ex-headmistress Valerie Bragg. She was chosen to project-manage the creation of the academy by the school's private sponsor Sir David Garrard, executive chairman of Minerva property group (see "The business brains behind Bexley", page 8).

Bragg's vision of having an open-plan school provided the acoustic consultant Harris Grant with a design and specification headache. The variety of teaching space – much of it open-plan – had to be designed so that pupils and teachers would not be disturbed by noise from other classes. To meet the "open and transparent" demands of the brief, Foster incorporated glass walls to visibly connect the staff and students. A sensible philosophy, but it meant that Harris Grant had to mitigate the echoes caused by the large expanse of glass. "Echoes break down intelligibility very quickly," explains Neil Grant, Harris Grant's managing director.

The problem was compounded by the hard concrete surfaces Foster had left exposed in order to provide the thermal mass necessary to cool the building interior. Added to this was the tight timeframe – the school had to be built in only two years, and there would be little time for remedial work if the acoustic strategy failed.

Fortunately for the design team, Bragg was aware of the potential acoustic problems and had made sure that Harris Grant was involved in the project from the start. "Before there was even a hole in the ground, we were modelling the sound. It was an unusual and pleasing circumstance to be involved in the project from the beginning. We were able to make everybody on the design team aware of the problems," says Grant.

He was able to analyse the noise characteristics of the teaching space before construction began by using powerful acoustic software called CATT. After feeding in the acoustic measurements of the surfaces, the program calculated the acoustic performance of each area.

To deal with the reverberating echoes in the three internal courtyards, Grant came up with the idea of suspending baffles from the ceiling. "Baffles are used in warehouses and factories to absorb sound," says Grant. "It occurred to me that we could use them to do the same thing here."

The baffles provided an elegant solution. They followed the same lines as the steel structure so were discreet and did not impede natural light from entering the courtyards. Mineral wool and fibreglass were specified for the baffles to provide a high level of sound absorbency. Rows of baffles resembling small louvres were also used at the top of the glass walls to provide further acoustic insulation.

In the ground-floor teaching spaces, a 25 mm sealed glass unit was specified to provide acoustic protection. The specification had to be high, because some of the teaching areas contain noisy machinery, such as potter's wheels, saws, routers and cooking equipment. The glass unit consists of two gas-filled layers of glass, which are laminated and toughened.

The classrooms on the upper levels overlook the art, technology and business courtyards, and have no walls to protect the students from noise. Instead, acoustic protection comes in the form of toughened glass balustrades fixed to upper-floor galleries and bridges.

Harris Grant also managed to provide a high level of sound absorbency in the classrooms without spoiling Foster's designs. Perforated steel trays backed with sound-absorbent fibreglass batts were specified and suspended from the concrete slab. This meant that the concrete was left exposed, allowing the thermal mass of the slab to passively cool the classrooms. The steel trays were also used to conceal lighting and conduits carrying cables and services.

Harris Grant also used the CATT model to determine the material to be used for the flooring. Originally, hardwood flooring was to be specified but after analysis, it was found not to have sufficient sound absorbency: a 9 mm carpet and rubber tiles were specified instead.

Teachers have given the completed school top marks, according to both Bragg and Harris Grant. The say they like the atmosphere, and interference from other lessons did not seem to be a problem.

However, the design of Bexley Business Academy will pose an interesting conundrum for the government, as its open-plan design may not comply with acoustic building regulations, which came into force on 1 July this year.

Part E of the Building Regulations refers designers and specifiers of school buildings to Building Bulletin 93, which offers guidance on acoustic design. It sets tough standards on the transfer of sound between teaching spaces, something that some of Bexley's open-plan teaching spaces cannot achieve.

On the ground floor, all the teaching spaces – apart from the three large courtyards – are sound-protected E E by thick glass. On the upper levels, it is a different story: many of the classrooms and teaching spaces that overlook the courtyards only have a glass balustrade to separate them acoustically from the rest of the school.

As BB93 demands high levels of sound insulation between classrooms, Bexley would probably have failed to comply with Part E if it had been built after 1 July. But Grant says there might be a get-out for schools with large open-plan areas. Although BB93 strongly discourages the simultaneous teaching of several classes in open-plan spaces, it states that such spaces can be built if there is a demonstrable need for them and if it can be proved by acoustic modelling that they have a high level of speech intelligibility.

Valerie Bragg is delighted with the finished building and is satisfied that her vision has been realised.

"I had some battles, which was good. I've made sure it's an operational building and not just an architectural one," she says.

Bragg claims that the open-plan nature of the academy does not limit the ability of staff to teach and of children to learn. The proof, says Bragg, is the positive experience of the teachers. "The staff really like it and it works," she says.

CABE's Stuart Lipton and Tony Blair are also fans – whether the building control officers who enforce building regulations will be admirers of similar new schools remains to be seen. If more open plan schools are to be built, local authorities will have to give experts such as Harris Grant the chance to prove they can provide high standards of acoustic performance without having to stick too rigidly to the rules …