Ruth Slavid reports on how Scott Brownrigg salvaged the ‘bones’ of a typical 1980s commercial building in Bristol to create an understated, sleek facility with greater capacity, and passive design measures to sustain it into the future
The new Aztec 1000 building at Bristol’s Aztec West business park is very much of its time. It has a cool, understated look, facades that respond to the orientation, and generous gym and eating spaces. It bears very little resemblance to the type of brash, brightly coloured – and environmentally reckless – building that was common from the period of its completion – the 1980s.
And yet, the bones of just such a building are contained within the new facility. Architect Scott Brownrigg has kept the 1980s frame, extending the building both upwards and outwards. Ed Hayden, director at Scott Brownrigg, explains, “As a company, we take a ‘retain and refurbish first’ approach. We ask: ‘Can we retain it flexibly?’” In this case, he says: “It would have been very easy to demolish and rebuild from scratch.” Instead, the practice worked closely with the client, Commercial Estates Group (CEG), to retain the frame and extend from there.
There was no question of keeping the building in its original form since it was not fit for today’s needs. Indeed, it had not been a success. A two-storey, L-shaped structure, its steel frame was exposed externally, causing cold bridging. The building was originally designed to be naturally ventilated, but this ventilation came from opening a series of sliding doors. The security implications deterred occupants from doing this. As a result, the building overheated and air conditioning was retrofitted.
The other main issue was with the plan. The core sat at the junction of the ‘L’ and blocked communication between the two wings. This was a building that was, at the time of construction, intended for single occupancy, making this problem severe. Other drawbacks included a lightweight roof, making it impossible to plant on it, and a low floor-to-ceiling height. At only 2,600 mm, this was less than the BCO minimum standard of 2,750 mm. The distance from the finished floor level to the underside of the structural steel was about 2,800 mm. For all these reasons, the building had ceased to be viable and was abandoned. CEG approached Scott Brownrigg, a practice who it had worked with before, to find a solution that would improve the attractiveness of the building and provide more space and a better environmental performance.
Demolition and new build would have been the simplest solution, but Hayden was certain that retention of the original frame could work and convinced the client. The decision was, he said, ‘cost neutral’. Having looked at all the negative elements, there were also a number of positives that the new design could exploit.
Aztec 1000 is at one end of the Aztec West business park, a 68 ha development on the outskirts of Bristol. It’s in South Gloucestershire, near to the M4 and M5 motorways, and next to the A38 trunk road. Development started in the early 1980s, at a time when good road transport was considered essential, and sustainable travel was not a major consideration. The name Aztec was believed to derive from ‘A to Z of technology’ and the scheme’s original role was as a science park.
Some distinguished architects designed buildings there, including Nicholas Grimshaw, Michael Aukett, SOM and CZWG. In 2018, selected buildings on the site were listed. Evidently, Aztec 1000 was not a candidate. However, what it lacked in architectural pizzazz, it made up for in orientation and position. It sits at one end of the central zone of the park, encircled by a pedestrian path that is roughly the shape of a race track.
The building is beside a lake, with one wing looking out over it, providing potential for a pleasant outlook. Scott Brownrigg has made this part of its design, providing a terrace where occupants can look over the water.
The architect has tackled the problems, creating more and better space. It removed the lightweight roof and replaced it with a new floor structure for an additional floor and a stronger new roof. From two storeys, the building now has three, with the ability to site some plant plus solar panels on the roof.
Retaining the facades was not an option. Modern day glass can be specified to have a far superior performance, and it was the design of the original facades, with their opening doors for ventilation, that proved unsuccessful in terms of usage, and resulted in the original introduction of air conditioning.
The structural engineer, Curtins, looked at a variety of structural solutions to provide additional space for the client. These included extending upwards (on which it finally settled), as well as extending laterally, and an entire rebuild.
The engineers carried out detailed structural investigations to assist with understanding the load paths of the primary frame, and to confirm the ground conditions. Local strengthening was introduced to the steel frame and to the pad foundations. Hayden comments: “We now have rather dramatic cross bracing on the facades, which we have made a feature of.”
There is also a new concrete core that helps to stabilise the structure. This also overcomes the problem of the original core blocking circulation. The new core has been added inside the bend of the plan, turning a single right angle into a pair of 45° angles. This additional triangular element, filling in the knuckle, increases the depth of the building at this point. The glazing provides as much transparency as possible. “You can see straight through to the lakeside,” Hayden explains. The core contains stairs and two lifts, and the building is fully DDA compliant.
This change increased the depth of the building at this knuckle and allowed the design team to transform the way that the ground floor is used. The central space now contains a restaurant, cafe & meeting area as well as a gym. These can be used by tenants of the building, and also by other tenants of Aztec West.
Hayden explained that this reflects the way that working practices have changed since the original business/ science park was built. In addition to any meeting rooms that tenants choose to put into their own spaces, the new social spaces on the ground floor, outside on the lakeside and on the roof terrace will facilitate the informal encounters that play such a vital role today in creative thinking and collaboration. This was identified as a vital element as post-Covid, meetings and interaction are the main reasons for going to the office – we all have the facilities to write an individual report at home. Beyond that, he says: “Part of our thinking is about the location at the southern end of the park. There are few facilities that can be used by the tenants. These spaces should foster collaboration across the park. And the architecture should create a buzz.”
There is also a dedicated space for cycle parking and a roof terrace that tenants on the top floor will be able to use.
Taking the glazing beyond the original frame provided two benefits. It increased the floor area and it also solved the problem of the cold bridging that resulted from having an external exposed steel frame. The new enclosure is fully glazed with high performance glazing, allowing a high degree of light penetration into the space, which is only 16 metres deep. The southern elevations (effectively the ‘inside face’ of the L) have aluminium ‘light shelves’ incorporated in the curtain walling. These serve the double function of shading the facade from the sun and bouncing light deep into the plan.
The ends of the wings have vertical fins that reduce the solar gain in the morning and the evening when the sun strikes, respectively, from the east and the west.
The sealed box design approach should ensure that there are very low levels of air leakage.
Internally the main concerns were to create flexible spaces, to maximise the floor to ceiling heights and to improve the environmental behaviour of the building. There are no internal columns on the upper floor, allowing tenants to put in meeting rooms, partitions and so on wherever they decide to. Each floor will be able to accommodate two tenants, making a total of six, although larger tenancies will also
be possible.
The floors are concrete planks, and the soffits have been left exposed, allowing for night-time purge cooling, which is a part of the environmental strategy. The exposed concrete will, says Hayden, retain ‘coolth’ in summer. ”The engineer and client perceived this as a very positive move, “ Hayden comments, because it gives additional height, ”which was important especially on the ground floor with the restricted floor to floor height.”
With such a hard ceiling, there was evidently potential for acoustic problems. Scott Brownrigg has dealt with this by using soffits suspended acoustic rafts which contain sound-absorbent mats which reduce the reverberation. This approach uses far less material and therefore embodied carbon than a full ceiling system, while not affecting the perceived height.
Shallow raised floors house essential services. Kept to a minimum. These allow a distance from the floor to the underside of the services of 2.55 metres (on the ground floor with the retained frame). The impression is of openness, coupled with the relative shallow floor plates and the generous glazing, the design has avoided the oppressiveness that is too often associated with limited ceiling heights.
Wherever possible, the building uses recycled materials. For example, the upholstery fabric is 100% recycled and half of that is made from marine plastics. Other elements, such as the vinyl used in the kitchens and on the gym floors, have a substantial recycled content. Hayden comments: “Both we and the client are exponents of the re-use of materials”. “Due to the reduction in embodied carbon, this is the correct approach to embrace a ‘circular economy’ mindset”.
The original design was in modular 6 metre bays, and the design team has taken advantage of this in its environmental strategy. Although there is some plant on the roof, most of the climate treatment happens not only on a floor-by-floor basis, but on a bay-by-bay basis. This means that if part of the building – a floor or just a bay – is not occupied, then the heating and cooling can be switched off, saving energy. The design services engineer Cudd Bently, who developed the final solution for the M&E services, designed an overall BMS for the building , but much of the control is at a local level.
Vents at each floor level draw in naturally cooled air from the lake side of the building, taking advantage of the cooling properties of a body of water. Conditioning is then carried out by the floor-based plant.
Hayden explains the integrated ventilation approach further: “Working with the M&E designers at an early stage has allowed us to design a fully integrated solution where architecture and services are working together to create a united low energy solution is fundamental when designing for low energy use.” He continues: “A great example of this is using the lake-side setting to draw in cool air from the waterside into each bay of the floor plates. The pre-cooling provided by the lake ensures we minimise the energy required for conditioning the internal air temperature.”
Solar panels on the roof are deliberately oriented east and west, rather than south. What this does, explained Hayden, is flatten the curve of power output. Because battery storage on a building scale is still not commercially viable, electricity can only be used or sold back to the grid at the moment that it is generated. Flattening the curve means that, while the peak output drops, there is more usable electricity over a longer period. This therefore increases
the proportion of electricity generated by the panels that the building can use. The team developed this concept during the project design, in conjunction with the specialist subcontractor.
The building has been designed to be zero carbon. CEG employed sustainable energy consultant Cudd Bentley to review and verify its plan. The client has substantially more floor space, thanks not just to the additional floor but also to the enlarged footprint. Users, whether sitting out on the terrace, or using the canteen and gym, will have a building that enhances the quality of their working day. And this will apply not only to the tenants of the building but also to others within the business park.
Hayden is clear that Scott Brownrigg designs every job to fit the particular circumstances of the building and the needs of the client. But there is one lesson that he will carry forward to future projects. “We have learnt the importance of the modularity of air conditioning and other kit,” he says. “Utilisation varies through the building. We think this approach is a key part of conserving energy.”
The architect has given the client a building that is fit for present-day use, with good environmental credentials and additional space. The open aspect and shared space mean that, instead of the previous, outdated building, it is now an office whose spaces align with modern ways of working.
Hayden concludes on how this building exemplifies how Scott Brownrigg places a priority on reuse as a means to sustainability: “We believe that the first step in achieving true sustainability is to retain as much of the existing material as is practically possible and to build passive energy and carbon saving strategies into the layout and fabric of the building.” Scott Brownrigg’s ambitions have been realised, in a workspace that is rated BREEAM Excellent and boasts an ‘A’ EPC rating. And it’s a full vindication of the decision to retain, and adapt.
Photography © Neil Waving