Green Sky Thinking: ‘Retrofit: Do It Yourself?’

When it comes to a retrofit project, a client is wise to exercise malleable expectations from the outset.  This was one of several ‘lessons learnt’ demonstrated by Cullinan Studio at their Green Sky Thinking event, where they discussed the recent retrofit of their own new canal-side offices in Angel, Islington. Prior to the conversion this three-storey post-industrial building, historically a foundry, was one of the few that remained relatively untouched in the area. At the event, the project’s director Johnny Winter spoke candidly about the whole process from planning right through to post-occupancy data. It is notable that the project still managed to achieve BREEAM Excellent, despite its significant constraints.

Johnny Winter explains the structural strategies employed

Having bought a large portion of Baldwin Terrace in 1991, Cullinan Studio chose the central building in the terrace to become its new home. The practice initially set out with high expectations of their own time, budget and manpower. Johnny joked about their well-meant positivity, which spurred them into hoping they could morph the building into suitable offices during weekend DIY sessions over a three month period. However, as the end of their lease in Camden drew near, they were forced to retreat next door, to a more structurally sound and adaptable building they had earmarked for redevelopment into flats. Here they were to remain “temporarily” for the next 20 years. In the meantime, the old foundry building was rented out as artists’ workspace and an exhibition gallery.

  

Whilst in retreat next door, the practice spent time on an ambitious design to replace the old foundry building, only to have the planning application rejected upon submission in 2004. As the practice took stock and redesigned, a planning conservation officer revealed the significance of the canal-side wall, which was deemed of special interest due to its position on the edge of a conservation area. The retention of this wall, along with the timber trusses spanning the roof, became a key planning condition, and inevitably a driver for the whole redesign. The wall required serious structural intervention, with its upper edge listing 180mm out toward the canal. After quite a struggle, planning permission was finally achieved in 2008, although unfortunate timing with the recession meant the project still stalled for another three years before construction.

Building tour: the retained timber trusses 

The approved design kept the building structure and listed wall intact but planned a ‘fabric first’ approach of super-insulating the walls, floors and roof. The recycled newspaper insulation on the canal wall ended up particularly thick; sprayed on up to 450mm deep in places due to the undulation of the wall. Despite the structural constraints and the preservative approach to the building’s fabric, the practice endeavoured to create a dynamic working environment, by ensuring all three levels were visually and acoustically connected in section. The Green Sky Thinking audience was curious as to whether the practice had considered further negotiation with the conservation officer. Johnny was almost certain that the issue was non-negotiable – had the practice gone to appeal there was a risk that the whole building could have ended up listed, upending the whole design process.

Yet in the end, dealing with the listing wall proved to be a defining architectural feature of the project. The engineers for the project, Price & Myers, had originally designed a temporary retention structure to hold the listing canal wall, while the existing trusses were taken away for cleaning and storage during the main building works. A permanent steel retention structure would then be installed after. However, the practice was keen to reduce the hassle and the waste of two separate structures, and so redesigned the scheme with in-house structural expertise to include a singular Vierendeel truss (amusingly mispronounced by the contractor as a “venereal truss”). This truss could be installed as a permanent retention structure at the same time as the footings. When construction finally began in 2011, the listing wall now 250mm out of plum, necessitating some temporary bracing prior to installation of the Vierendeel. The building’s dynamically connected levels were also simplified in both plan and section, retaining two linked floors for the practice’s use and a separated top floor, meaning they now had a lettable space.

Building tour: the mezzanine overlooking the Vierendeel

The energy-saving practices implemented on the project were subject to several recognisable issues. Four years after the application the planned methods had become either unattainably expensive or outdated; the canal inlet could not be used for water-based cooling due to hefty British Waterways fees and a wind survey revealed the planned five turbines would not produce a worthwhile output. In place of these other tenets of sustainability had to be amped up, such as the aforementioned fabric retention, the use of recycled newspaper and super insulation. Indeed the fabric detailing has worked favourably with a pressure test of less than 5ac/h, an encouraging measure for an existing building. The offices are naturally ventilated, the pleasantness of which was confirmed on the day the Green Sky Thinking event by the mild spring air percolating in from the Regent’s Canal.

Now that the building has been occupied for a few months, Cullinan Studio have been able to take stock of its energy use. Johnny noted that the Building Management System (BMS) has provided them with some data, but has been frustrating due to it being almost too specialised. So they have been able to identify when and how the building is malfunctioning but not why! The existing lift overrun now houses an air source heat pump that serves all the building’s heating needs, contrasting with the 22m² of photovoltaic panels, which have supplied a modest 600kW since October 2011. A question cropped up here: why didn’t they design in a larger array? It was an obvious cost issue, but there was a suggestion from the practice’s own Robin Nicholson that the amount of VAT paid for the conversion could have been better spent on more photovoltaics. Cost reductions have also meant insufficient absorptive acoustic material on the canal-level floor, causing kitchen noise to reverberate up into the mezzanine – an ongoing issue that will be rectified in due course.

Robin Nicholson on current planning attitudes

Looking to the future, with a dwindling postindustrial landscape left to be canabalised, the retrofit issue is quietly gathering gravitas. When it comes to building conservation versus the imperatives of energy-use reduction, the balance will have to shift. This was neatly summed up by Robin, who used the example of planners’ reluctance to retrofit Georgian sash windows with double-glazing to show that “planners need to wake up to retrofit”.

Meanwhile, in the case of Cullinan Studio’s Foundry, the necessity of retrofit made for a more challenging and interesting project. At the start of the project, retrofit was not the go-to option, rather it was resultant from a circumstantial cocktail of economic climate and planning conditions. Of course, the audience was keen to know if the practice would still have chosen retrofit without the imposed planning controls. Initially Johnny said he would have taken down the building and rebuilt, hopefully using reclaimed bricks from the site. However it was the process of engaging in retrofit that has actually swayed that original stance, and that “seeing an old building injected with a new lease of life was inspiring.” It is hard not to agree, the resulting building has become an object that is both pleasantly bespoke and inherently of its place.