Standing tall: Cedar Court

As standards rise for new build, the contrast with the energy inefficiency of our existing building stock, and the urgency of addressing it, becomes ever more evident. In Glasgow, as in many other cities across the UK, older tower blocks and housing schemes seen to no longer be adequate have frequently been earmarked for demolition and replacement. But the squandering of embodied carbon through demolition, added to the emissions costs of replacement construction, invariably results in a much higher total carbon emissions budget for a project than would a refurbishment, adaptation or reuse solution, as well as costing more.

The recent completion of the refurbishment of three high rise towers in the Woodside area of Glasgow, targeting the EnerPHit standard, has demonstrated how successful the alternative can be: deep retrofit at scale. Queens Cross Housing Association’s Cedar Court and Cedar Street, built in the 1960s, now look like new, and perform better than most new builds, providing warmth and comfort to the tenants of 314 homes.

 

We made a business plan commitment to invest in our multi-storeys. Our objective was transform them in to some of our most desirable homes, to improve residents’ lives and enhance the city skyline. This project is the most ambitious the Association’s undertaken to date. Properties with improved thermal performance helps us meet EESSH compliance by 31 December 2020. This supports the Scottish Government’s vision of warm, high quality, affordable and low carbon homes.

Queens Cross Housing Association 

 

Key team
Project Owner/Client: Architect and Passivhaus Designer:    Structural Engineer:  Contractor: Air testing: Certifier:	Queens Cross Housing Association    Collective Architecture Cundall Engie Thermal Image UK WARM

By retrofitting rather than demolishing, the associated whole life carbon is likely to be closer to Net Zero Carbon than most new builds. A fabric first approach allows energy savings to be locked into the building fabric for the life of the building and mean that any subsequent local renewable energy generation would represent additionality rather than simply offset poor building performance. This approach would also help improve comfort and wellbeing for the residents whilst improving air quality via mechanical ventilation with heat recovery. 

Rupert Daly, Project Architect/ Passivhaus Designer, Collective Architecture

Before the project could start, to answer the question of whether the towers could indeed be saved from the wrecker’s ball, their structural integrity first had to be assessed. PHT member Cundall found the concrete crosswall construction had held up well, with any cracking and spalling found on exposed elements considered reparable. The green light was given for PHT member Collective Architecture to take forward the highly energy efficient retrofit, aiming for EnerPHit certification.

 

Before the refurbishment could be considered it was necessary to assess the buildings and determine that the structure would perform satisfactorily for the next thirty years or more. Cundall assessed the building using archive information as well as employing visual and intrusive investigations to determine chloride and sulphate levels, depth of carbonation, concrete quality and strength, and the extent of cracking and micro-cracking. The assessment demonstrated that the proposed refurbishment was structurally feasible and overall the towers were in good structural condition given their age. This project demonstrates that some high-rise towers can provide sustainable affordable housing for the future.

Neil Dely, Civil & Structural Engineering Partner Cundall

 

One of the major obstacles to overcome when taking on deep retrofit of an existing residential building is the disruption to those who live there. To empty a building for many months and provide satisfactory temporary accommodation for residents places additional pressure on the build schedule, adds an extra level of complexity to what is likely to already be a challenging project, and of course inconveniences the residents. Decanting residents was avoided by pursuing a strategy that allowed the them to remain in-situ for the duration of the work. The building has been wrapped externally in Rockwool mineral wool for economy, efficiency and fire integrity, finished with a self-cleaning render. High rise apartment blocks are ideal in form for Passivhaus, with a very efficient ratio of surface area to volume, so insulation of just 120mm across most of the building and 160mm to the gables has been sufficient to meet the EnerPHit targets.

Another challenge that recurs in retrofit projects is what to do with balconies, which create major cold bridges where they join the main structure, and would obstruct any additional insulation. Rather than simply cut them off, a solution that was considered and that others have employed, instead they have been externally insulated, supported with new thermally broken structural elements, and enclosed with triple glazing. Cold, exposed and unloved spaces have been transformed into comfortable wintergardens, already proving popular with residents. The vivacious yellow flashings enliven the facade to create a characterful new aesthetic.

 

 

This has been a challenging and a technically difficult, but an enormously rewarding refurbishment to be involved in. We truly believe this has been a remarkable achievement for ENGIE and our design team.  Bringing to fruition the fantastic improvements to the residents through innovative design and functionality by means of additional formed amenity spaces such as winter gardens which have totally transformed the exterior of the facade in rich vibrant colours. We’d like to show our appreciation, thanks and respect to all the residents in the tower blocks who, over the course of the contract, have shown tremendous patience, cooperation, goodwill and assistance to all our efforts to improve their daily lives.

Tom Cuddihy, Project manager, Engie

 

Key facts
Build start date: Date of occupation:    Number of towers: Number of flats: Cost:	January 2016    October 2019 3 314 £13.3 million

All that remains for the building to be ready for EnerPHit certification is an upgrade to install higher grade filters into the MVHR units, and a final airtightness test. Although conducting a retrofit while residents remain at home offers huge advantages of minimal disruption and cost efficiency, it does leave the challenge of airtightness testing to be resolved. Interim testing, carried out by PHT member Thermal Image UK, has indicated that targets are being met, and a solution to how to conduct a final test is being sought. Once that solution is found, EnerPHit certification could be achieved.

This ground-breaking project is of global significance, and a real testament to the skill and commitment of the whole team, especially the contractor Engie, and client Queens Cross Housing Association, for whom this is their first Passivhaus project. Deep green retrofit is challenging and large-scale EnerPHit projects are scarce not only in the UK but worldwide. If certification is achieved, Cedar Court is in line to become the largest EnerPHit in the world.

 

All images © Andrew Lee and Collective Architecture

EnerPHit at scale

At another crosswall scheme in Scotland, the Passivhaus Trust, together with partners BRE, PHT member John Gilbert Architects, and the Construction Scotland Innovation Centre, is exploring how to reduce domestic retrofit costs whilst delivering lower carbon performance and reductions in fuel poverty. Working with Renfrewshire Council, 75 council owned homes in the Paisley area will be upgraded with a series of deep retrofit measures, funded through the Department for Business, Energy and Industrial Strategy (BEIS) Whole house retrofit competition. Find out more.

 

Further information

Previous PHT story: Scottish Passivhaus projects update - 28 June 2016

Cedar Multis: UK Passivhaus Conference 2016 presentation [PDF]  - Rupert Daly, Collective Architecture

Passivhaus Retrofit

Cedar Court and Cedar Street: Woodside multi-storey flats | Collective Architecture

Getting warmer: Collective Architecture upgrades Glasgow tower blocks | Architects Journal - 7 November 2019

 

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30th November 2019

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