Organised by NLA and hosted by HTS, ‘Technical Competency: Retrofit’ brought together experts and practitioners from across the built environment to discuss the latest methodologies and technical innovations in retrofitting. 

 

The Kensington Building was presented by Tal Ben-Amar, Founding Partner of architects and urban designers Pilbrow & Partners.

 

The panel of experts included Federico Ortiz, Head of Research at NLA, Mark Tillett, Director at HTS, Azzahra Mahmud, Senior Structural Engineer at HTS and Jessica Foster, Associate at Civic Engineers.

The Kensington Building; the process, the challenges and the achievements

With the rapid advancement - and increasingly evident impact - of climate change and the acknowledged destructive contribution from the construction industry, we all need to be more ‘climate conscious’.  

 

The retrofitting and repurposing of existing buildings is one way that we can significantly reduce our industry’s carbon footprint whilst still providing attractive and efficient accommodation.  

 

The Kensington Building is an example of how an essentially redundant structure can be reimagined. Refurbished - retrofitted - the building now meets modern environmental standards and provides relevant, adaptable and contemporary workspace.

 

Located at the corner of Kensington High Street and Wrights Lane, the recently completed Kensington Building was the former site of Pontings department store. 

 

The 1970s building occupied a prominent position adjacent to Kensington High Street Underground Station and presented a robust, reinforced concrete frame (10KN), sound foundations and floor-to-floor heights of between 4.5m and 5m. 

 

Whilst the location, sturdy frame and generous internal space combined to offer great potential, the building also had many architectural - and urban - shortcomings:

 

 

Working with the 1970s building was both a challenge and an opportunity. 

 

The challenge was urbanistic. A brutalist structure, the original building eroded the historic definition of the surrounding streets.

 

The opportunity was the generously proportioned interior space. High floor loadings allowed the building to be extended and remodelled with sensitivity.

 

The retrofit of The Kensington Building adapts and remodels the former department store to deliver 95,000sqft of BREEAM Excellent workspace and 34,000sqft of retail space. This represents an increase of circa 50% over the original building.

 

Externally, the architecture restores the historic alignment on Wrights Lane with high quality brick and stone elevations, sensitive to the traditions of Kensington.

 

Internally, the design celebrates the retention of the original structure which is left exposed within the lower office floors. There is a considered balance between old and new, particularly at the interface between the new brick and stone façades and the underlying structure within. Here, the alignment and indeed misalignment of the historic and contemporary grids enrich the elevations.

 

The quality and quantum of office space is increased. Flexible, environmentally sustainable workspace is now served by a core set on the eastern boundary next to the underground.

 

The upper office levels step back to create a sequence of landscaped terraces, introducing biodiversity and enhancing the outlook for both office users and neighbours.

 

Public realm is improved through the creation of a new arcade connecting to Kensington High Street Underground Station. 

 

The ground floor retail offer is elevated with Boots retained as the anchor tenant. Smaller scale, independent units activate the galleria.

 

The Kensington Building enjoys exceptional public transport links and provides 165 cycle parking spaces, showering and changing facilities to encourage cycling to work.

Not every building is suitable for retrofitting. However, in the case of The Kensington Building, reutilising the superstructure frame of the former Pontings Department Store made a substantial contribution to reducing embodied energy as well as minimising construction disturbance, traffic generation and material excavation to land fill.

 

This approach fully exploited the underutilised structural capacity of the existing frame. The department store was built with 5KN/m2 live load allowances, well in excess of that required by the proposed office use. We were able to utilise this live load allowance to support the three additional storeys of accommodation created in the refurbishment.

 

The retained superstructure forms an integral part of the building’s environmental system. Developed with WSP, the superstructure is exposed and serves to passively temper the internal atmosphere. Air is delivered from the floor which allows free-cooling to be exploited in mid-season. This displacement system is associated with higher air volumes and less air mixing.

 

Sensor controls maximise operational efficiency.

 

Horizontal surfaces are optimised to provide landscaping with sustainable urban drainage or plant; the latter is integrated with on-site renewables with an expected annual energy production of 12,000kWh.

 

Calculations of embodied energy suggest the total building embodied energy (A1 to A5) is 700kg/CO2eq/m2. An equivalent new build would have embodied energy characteristics twice as high as this figure.

 

Sustainability, character, social and economic infrastructure and sense of heritage should be the key considerations when assessing the benefits of choosing retrofit or new build.  It is worth noting that retrofit projects would typically not be cheaper to construct and require ambitious and forward-thinking clients along with more experienced design teams and more specialised contractors.

The fact that public debate around retrofitting has started and that there are more and more projects re-utilizing existing structures are great steps towards achieving a Net Zero future.