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18/01/2011
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Whitecross High School

Hereford

Process

The brief contained stringent sustainability requirements, and this became the key driver for the design process. This has been made visible in the buildings, so that the school can educate its users. All services are exposed, and read-outs from the Building Management System (BMS) are shown on the school’s energy meter display at the front of the school.

An early decision was to use a concrete structure with high thermal mass for the teaching spaces. This greatly reduces the changes in temperature during the course of the day as the mass acts as a heat, or cold, sink, absorbing and releasing energy at a slow rate. A system was adopted of cooling or heating the slab overnight, using low velocity mechanical ventilation, to ensure even temperature distribution within the building. Linked to this was a decision that the insulation levels should be much greater than the current Building Regulations. A typical u-value of 0.15W/m²K was stated by the Green Team as an appropriate target. The high level of insulation reduces the effects of extremes of external temperature, helping to maintain minimum comfort levels. In winter, a class of 30 will effectively self-heat the classroom up to required temperatures very quickly, reducing the heating load from the boilers.

The school is mechanically ventilated to ensure that the low energy targets did not compromise user comfort. This allows rates of air change and night-time cooling, to be controlled, reducing CO2 build up during the day and keeping students alert. Heat is recovered from the ventilation system which helps to pay back the energy costs of running the mechanical ventilation.

Another crucial aspect of the sustainability approach was to maximise air-tightness and daylighting, whilst reducing unwanted solar heat gain and glare. Design and sequencing workshops involving all parties, including the builders, were held to ensure that very high air-tightness was achieved. Post completion tests have shown that this has been successful.

Orientation of the blocks was the key to ensuring that day lighting was maximised and direct sunlight minimised. All south facing classrooms are shaded by brise soliel on the first floor, and the ground floor classrooms are shaded by the projection of the first floor classrooms. The first floor spaces contain teaching spaces lit from both sides through clerestory glazing on the corridor side. This reduces the energy requirement for artificial lighting.

Biodiversity and surface water attenuation have been addressed in the design. Large expanses of roofing have been covered with a sedum roof finish. This helps to replace landscape and habitat on a former green-field site and attenuate water run-off. The scheme has planning permission to erect an electricity generating wind turbine; the infrastructure is already in place and, once installed, it is estimated that it will produce up to 8% of the energy requirements of the school.

Haverstock Associates put a lot of emphasis on spending time with the school and its pupils during the bid stages. The headteacher has said that this was a major consideration when selecting Stepnell as their preferred contractor. The headteacher did not want a ‘street’ approach, and the students liked the idea that they would partly circulate externally and have fresh air between lessons. Another design principle was to avoid narrow corridors without daylight. Although circulation spaces are generous, they have not been designed as break-out spaces. Instead the headteacher has opted to use workrooms or dining areas for small groups. Also, at 60m2, the classrooms are a more generous size than the normal government recommendation.

The services of a CABE enabler were provided in the early stages of the project. He helped the school to understand how their educational vision might translate into new buildings in practice. He contributed to the bidders briefing day, and was able to emphasise to potential bidders the importance of design quality. He also helped the staff understand school design issues in readiness for the bidders’ submissions. His involvement ceased before the bid evaluation stage.