Making Retrofit work: a detailed look at the Bartlett School of Architecture
For World Green Building Week we’re revisiting how a ‘deep retrofit’ was the most effective option in reducing cost as well as carbon emissions in refurbishing the Bartlett School of Architecture.
The Bartlett School of Architecture building, known as Wates House, was built in the 1970s. The university has grown significantly since then – as student numbers increased, the school suffered a chronic shortage of space, confused wayfinding, poor accessibility as well as a lack of quality teaching, office and social spaces.
We were tasked with increasing as much usable area as possible within the building’s context, which straddles three sub-areas of the Bloomsbury Conservation Area, whilst nurturing the creativity of the school. We were also working with a capped budget and tight programme timescales.
Our solution was what we call a ‘deep retrofit’: a delicate balance of new-build, extension and refurbishment.
Our solution was what we call a ‘deep retrofit’: a delicate balance of new-build, extension and refurbishment.
Are we solving the right problem?
The initial project scope was a modest two-storey extension, window replacement and minor internal alterations. However, we discovered through stakeholder engagement that an extension would not address the chronic shortage of quality space, poor thermal performance or high energy demands, offering only a short-term solution to a more profound problem. We subsequently analysed a range of options, from ‘do nothing’ to a demolition and rebuild.
The structural analysis showed that each floor plate could be extended at the perimeter using the existing structure to provide the gross internal area required in the brief, when combined with a roof and side extension. To achieve this, the envelope needed replacing so we concluded that a ‘deep retrofit’ provided the optimal balance of time, cost and sustainability.
Embodied carbon calculations done using in-house embodied carbon measurement tool HBERT showing the relative carbon emissions saving for each retrofit option.
Embodied carbon savings
This approach not only retained memories of the original building, it was six months quicker and £10m cheaper to construct than a full demolition and rebuild. The option also saved 440 tons of carbon by retaining the original concrete structure. Given the relatively low floor heights of the building at 3.25m, a newbuild to typical academic standards would not have yielded as much usable floor area as retrofitting the existing building.
Our emission reduction tool, H\B:ERT, was in development at the time. Had we been able to use it during the design process, we would have benefitted from understanding the embodied carbon implications of the options as part of the decision-making process. This is a process we are embedding in all live projects at Hawkins\Brown.
440
Tons of carbon saved by retaining the original concrete structure
Whole life carbon analysis of three options – ‘do nothing’, new build and the deep retrofit, produced using energy data before and after the project completion.
Considering whole life carbon
We concentrated our efforts in reducing the whole life carbon for the project while providing a much-improved internal environment enhancing wellbeing and productivity. This includes considerations for operational carbon emissions.
Providing the building with a new high-performing brick envelope reduces operational energy demand, while leaving the thermal mass of the existing structure exposed aids passive heating and cooling. We used dynamic thermal and energy modelling to optimise the façade to minimise overheating and reduce cooling demand.
Material choices
The material palette is deliberately pared down to provide efficient material usage. The brick façade is low maintenance and long-lasting, while shading is provided using careful glazing specification and window reveals rather than additional elements. The raw concrete of the existing structure is not covered, but rather celebrated and contrasted with new plywood joinery to add tactility and warmth to the interior.
The building connects to UCL’s district heat network and uses solar panels on the roof. The green roof enhances biodiversity and reduces surface water runoff.
Through using H\B:ERT in our current projects, we have learnt that a visual way of communicating the value of building retention, such as this example at the Bartlett, forms a persuasive case for both planners and clients.
Lessons learnt
Creative analysis of existing structures and exploring their potential must be a part of any retrofit feasibility study. Although we opted for a deep retrofit as the best option for this project, we fully recognise that this is not a one-size-fits-all answer to every brief. We believe that every building project should consider the whole life carbon impact at early design stage.
Through using H\B:ERT in our current projects, we have learnt that a visual way of communicating the value of building retention, such as this example at the Bartlett, forms a persuasive case for both planners and clients.
Our Revit-based emission reduction tool, H\B:ERT, is free to download and use. The tool won the AJ100 Best Use of Technology Award in 2020.
Through using H\B:ERT in our current projects, we have learnt that a visual way of communicating the value of building retention, such as this example at the Bartlett, forms a persuasive case for both planners and clients.
Before and after
