Velux Sales Office

The brief for this building was for it to act as a showcase for its products, be a practical demonstration of products in an inspirational setting and become "the most photographed roof in Europe", and to demonstrate good environmental practice, both in terms of energy consumption and its use of the roof space.

The design comprises two complementary roof forms constructed from a glue laminated timber framework. The two roofs are different in character: the south facing roof – a concave sweep of blue green slate tiles - is visible from all approaches and contains an array of Velux windows. The convex north roof is clad in cedar shingles, and acts as the primary means for daylight to enter the building through a second array of windows and through the clerestory windows that join the two roofs together. The two roofs shear relative to each other along the east west axis, providing expression to the double-height boardroom at the east end of the building and a sheltered terraced area at the west end. The axis of the building is curved, to respond to the site topography, improve the views from either end of the building and present a welcoming entry to the site.

Layout

The building form is essentially a low mass, highly insulated timber envelope, surrounding the thermally massive construction of the office deck and the meeting and plant rooms of the lower ground floor. The thermal mass of the office deck absorbs heat generated within the building during the day, purged at night by allowing the building to naturally ventilate, drawing cool night air through the office deck structure. The high roof space, allows for stack-driven natural ventilation for most areas. The maximum air flow needed in summer will be achieved using a combination of automatic and manually operated computer-controlled openings. In winter, air quality will be monitored, and automatic systems will activate trickle ventilation.

Lighting

The north-facing and clerestory glazing means most of the building can be naturally day lit. Shading of the south facade glazing will prevent local overheating and glare using solar control blinds.

Automatic controls ensure general area lighting adjusts in sync with natural daylight levels. The approach here is to achieve low-level lighting of 300 Lux supplemented with task lights, rather than the conventional 500 Lux level throughout. This offers significant reductions in energy consumption, while task lights ensure user comfort and work-space quality.

Insulation

A high level of thermal insulation, allied to the use of low emissivity, argon filled double glazed units, provides comfortable working temperatures and saves energy. Particular attention has been paid to the air tightness of the construction.

Structure

The design of the building is aimed at durability, economy and sustainability of resource use. The structure has two main elements: the concrete structures both at ground level and for the elevated office area, and the timber structures forming the roof and other elements.

The superstructure is constructed using a glue laminated (glulam) timber frame. This provides a great deal of versatility in the final form of the building and is both structurally efficient for the scale of the building and environmentally friendly in its use of renewable resources

A series of timber glulam ribs spring from the upper level office area to carry the arched north roof. The front edge of the arch is carried by a timber column rising from the front edge of the upper office area and also carries the rear edge of the leaning south roof. The lower edge of the south roof is carried by a series of glulam beams, which extend beyond the eaves and bear on 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 is stabilised by fine cables to other elements of the structure.

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. The mass of concrete forms a thermal sink, which moderates the temperature in the associated spaces. The exposed mass of concrete is able to soak up heat in hot weather.

The elements of the structure are all constructed from self-finished natural materials where possible. This both limits resource use and reduces fit out, decoration and maintenance costs. The materials used will all age naturally over time, taking on a patina of their own. No external materials will be compromised by weathering.

Energy targets

The brief set out the following targets:

• energy consumption to not exceed 100 kWh/sqm/pa (total gas 56 kWh; total electricity 44 kWh);
• carbon dioxide production to not exceed 41 kg/sqm/pa;
• air tightness 5 cbm/hr/sqm of permeable envelope at maintained pressure difference of 24 Pa;
• building to achieve an "Excellent" BREEAM rating.

The targets for this project are within 10% of those set for the Building Research Establishment’s (BRE) Environmental Building at Garston. Achieving these targets will make the building one of the most significant low energy, low impact designs in the UK.