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A new angle on offices

An office headquarters for Velux in Kettering provides an interesting, low-cost, quality design in a brownfield setting

Apparently the name Velux derives from 'Ve' (Ventilation) and 'lux' (lighting). By founding its business on these two natural aspects of window and rooflight function, the company has had a head-start on justifiable claims to sustainability.

So when White Design was invited to design the new Velux headquarters in Kettering, apart from having to use the scheme proposal as a showcase for the product, it also had to ensure that the building complied with stringent environmental parameters as a way of broadcasting the client's environmental credentials.

The client's brief set out the following targets:

energy consumption not to exceed 100 kWh/m 2/pa (total gas 56 kWh;

total electricity 44 kWh);

carbon dioxide production not to exceed 41 kg/m 2/pa;

air tightness 5 cbm/hr/m 2of permeable envelope at maintained pressure difference of 24 Pa;

building to achieve an 'excellent' BREEAM rating.

The design of the building is therefore aimed at ensuring 'durability, economy and sustainability of resource use'. With three months to completion, the building is in line to be one of the most low-energy, lowimpact designs in the country.

Located on a relatively undistinguished brownfield site, the building stands out as an imaginative architectural approach to the site, to the town and to the office building genre.

The most obvious feature of the building is the cruck-shaped gluedlaminated (glulam) ribs, which are set along the full length of the plan.

These superbly engineered glulams, imported from Denmark, are set on concrete founds to form a segmented arch. Each pair of opposing ribs overlap at the ridge, providing a natural location for clerestory lights and a 'ventilation gap' in the finished structure.

The ground floor is slightly stepped to accommodate the changes in ground levels across the width of the building. On one half of the plan area, the double-height space shows off the structure to good effect. For the other half of the floor plan, the building has been provided with a mezzanine office area. Here, the complicated structural requirements are less apparent. At this two-storey part of the building, the front edge of the arch is carried by a timber column rising from the front edge of the upper office area, which also carries the rear edge of the leaning southern-most roof. The lower edge of the south roof is carried by a series of glulam beams, which extend beyond the eaves and bear on steel anchor plates set in profiled concrete pads at ground level.

The timber columns and south roof are designed to carry the additional load of a retrofitted balcony office area, allowing future expansion at minimal cost. This would be stabilised by fine cables to other elements of the structure.

Glulam beams have been chosen for their versatility and for their structural efficiency for the given scale of the building. Concrete is used in the lower levels, where mass is a requirement of the environmental strategy and durability is required of the structure in contact with the ground. As the site is known to be a source of radon, an impermeable membrane has been incorporated under the ground slab to prevent any transfer through the substructure and across any perforations within it.

A filtration layer beneath the membrane forces any ground radon to migrate to the building's edge.

Because the property is required to be efficient and cost-effective to run, the mass of concrete forms a thermal sink that moderates the temperature in the associated spaces (see AJ 22.2.01). The concrete floor has been power float finished so that, like the glulam beams, the surface can be left exposed. This means the maintenance costs should be kept to a minimum and, as importantly, the mass of the concrete, rather than being concealed behind plasterboard or other finishes, is better able to soak up heat in hot weather.

Notwithstanding the environmental remit required by the client, this building is an excellent example of the successful marriage of simple materials, well thought-through detailing and the benefit of good workmanship on site.

Working closely as a team from the start, the architect, the structural engineer and the services engineer prepared scheme proposals that were initially centred around paper models and rough, hand-drawn perspectives to assist the visualisation of the geometries, before their ideas were transferred to CAD.

David Noble of White Design says that, although the building is 'not complex, the building's form does demand exceptional attention to detail. In addition, its use of primarily natural self-finished materials means that there is no room for mistakes in construction.'

Considering all aspects of the project's buildability was therefore a vital aspect if the job was to succeed.

Even though the scheme was traditionally tendered, the eight contractors were given informal pre-tender interviews. The architect booked a hotel and invited prospective tenderers to examine the model, ask questions and discuss detailing before going to tender to ensure that all contractors were aware of what was being asked of them. This kept tender-stage queries to a minimum and also ensured a good working relationship among all parties, which was to continue into the contract.

The building form is described as 'essentially a low-mass, highly insulated timber envelope surrounding the thermally massive construction of the office deck and the meeting and training rooms of the lower ground floor'. It acts as a simple thermal store, absorbing heat during the day and releasing it at night. This aids the stack-effect ventilation draught, and the high-level vent openings are controlled by the building management system, programmed to ensure optimum energy efficiency results.

Similarly, automatic controls ensure that the lighting level is adjusted regularly to suit the natural daylight levels and provide approximately 300 lux throughout.

Although this is somewhat lower than the normal office levels of 500 lux, when supplemented with task lighting it is designed to keep running costs as low as possible while still ensuring flexibility and user comfort.

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