National Trust
Client: The National Trust
Architect: Feilden Clegg Bradley
Project manager: Buro Four Project Services
Structural engineer: Adams Kara Taylor
M&E: Max Fordham Partnership
QS: Davis Langdon
Brickwork: Glen Sims Contractors
Main contractor: Moss Construction
Bricks: Ibstock
Curtain brickwork helps the National Trust’s new HQ score highly in the sustainability stakes
Feilden Clegg Bradley’s striking new £10m central office for the National Trust in Swindon was generated by three principles: to be the most sustainable building possible within the budget; to offer the best possible work environment; and to provide the most appropriate contextual response.
All three factors have been deftly combined in the 7,300m2 brick-clad, steel framed building which, with its references to the Victorian railway sheds of Brunel’s Great Western Railway next door (now converted to other uses), has become a landmark itself.
Unusually, the roof largely determines the building’s form. Saw-tooth roof lights, used both for north light and for accommodating south-facing photovoltaic panels, are arranged diagonally across the trapezoidal plan. This creates three gabled elevations that are built in
Staffordshire blue brick.
In stark contrast, the colonnaded south facade features extensive glazing with cast aluminium grilles. This is the public side of the building and gives access to the shop and coffee bar.
The National Trust’s ethos required a wide range of sustainability features including extensive use of photovoltaics, enhanced thermal insulation, automatic lighting control systems, wintertime mechanical ventilation and the use of lime mortar.
Exposed thermal mass in walls and fair-faced concrete soffits help mitigate solar heat gains, helped by natural ventilation and night cooling in the summer. The distinctive roof cowls promote both stack and wind-driven ventilation.
As an inextricably linked element to the overall sustainability strategy, the 442mm thick external wall construction achieves a U-value of just 0.2. It is comprised of 140mm thick internal concrete blockwork, rendered internally to capitalise on the thermal mass; a 200 mm cavity containing 150mm high performance insulation; and 102mm thick external facing brickwork.
Feilden Clegg Bradley’s project director Jo Wright explains: ‘Overall, the brickwork has been conceived as a rippling curtain that is punctuated by openings, indents and projections. It responds to the polychromatic brickwork of the adjacent railway sheds not by colour diversity but by manipulating texture and module size.’
The base plinth is smooth Staffordshire blue stretcher bond; the central zone is made of reinforced, stack-bonded 215mm high clay blocks; and the gables revert to stretcher bond. To provide solar shading and glare reduction for office areas, the architect devised precast cantilevered brick fins that are expressed in heather-coloured stack-bonded brickwork.
Pigmented lime mortar was specified because it drastically reduced the need for movement joints, blends well with the brickwork and, as far as Wright is concerned, has a more interesting texture than cement mortar. Equally importantly, its minimal cement content will facilitate the future recycling of the bricks.
Sustainability lies at the heart of the National Trust’s philosophy, so it must be well pleased with this building. According to Wright, the project ‘demonstrates that significant improvements can be achieved over the performance of typical commercial buildings built to similar budgets’.
This assessment is endorsed by its ‘excellent’ Breeam rating and the fact that it is forecast to produce less than 20kg of carbon dioxide per square metre each year. With performance like that, surely even Brunel himself would have been impressed.