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How green are the RIBA Stirling Prize finalists?

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It is no longer acceptable for 50-60 years to be the assumed life of a high-carbon investment, writes Simon Sturgis

Looking at 2014’s six RIBA Stirling Prize finalists from a holistic carbon perspective, who wins? Clearly the winner must be an outstanding design with low operational energy demands. The enduring benefit to society which comes from architectural quality is in itself carbon efficient. Buildings which are valued and enjoyed by their users will have a longer life.

Environmental design innovation, as well as incorporation of the latest best practice sustainability measures, should be fundamental. This, though, is just a part of the carbon picture. What does the whole picture look like?

A RIBA Stirling Prize finalist should also be a sound carbon investment for the long term by demonstrating that it has made optimum use of resources and that its design is informed by an understanding of the building’s future life.

This implies durability, resilience, low maintenance, and ease of re-use. It is no longer acceptable for 50 to 60 years to be the assumed life of a high-carbon investment. When a building is assembled, it is made from materials that are ‘on loan’ from our environment. To reduce overall environmental impact, it makes sense to use recycled materials and to design for re-use and recycling.

Of this year’s six finalists, the Everyman Theatre best addresses sustainable low-carbon design in the round, with the LSE a close runner-up. What nudges the Everyman into the top spot is its extensive use of recycled materials. The Everyman re-uses resources already on site, and it is energy-efficient in use, with significant passive contributions. It is durably built and is already admired locally. It is a building our great-grandchildren will be able to enjoy.

And isn’t this the point: to ensure that the environment in which we live is habitable for those great-grandchildren? By contrast, I would venture to say that two or perhaps three of this year’s finalists may well be consigned to landfill before the end of this century. This is not sustainable.
The UK’s most prestigious architecture prize must encourage innovation in overall carbon emissions reductions. James Stirling was himself a great innovator. Stirling Prize judging should examine and encourage use of existing structures and recycled content, life cycle analysis, flexibility for re-use, disposal and recyclability. Ease of maintenance, replacement of parts and ultimate disposal are all carbon issues for the architect, and not someone else’s problem.

Buildings worthy of being Stirling finalists should go further than meeting existing environmental codes. This means thinking about embodied carbon and operational carbon together. Even though standards and legislation have yet to address embodied carbon, the Stirling Prize should point the way, by recognising buildings which are low‑carbon in every sense.

  • Simon Sturgis is a partner at Sturgis Carbon Profiling

Predicted annual operational carbon emissions plus analysis

25.5 kgCO² /m² - Manchester School of Art Feilden by Clegg Bradley Studios

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This is the only entry that includes a substantial retrofit. Recycling an entire building is a great low-carbon starting point. The new build parts of the School are BREEAM Excellent, but the Retrofit tower is only rated Good, which is disappointing. But this rating could be higher if the BRE gave proper credit for the embodied carbon emission benefits of retrofit. The glazed area of the tower has been reduced by 40 per cent, contributing to improved energy efficiency without compromising daylight factors.

The school has a number of impressive sustainability measures including solar thermal, rainwater harvesting, mixed mode ventilation and heat recovery. An important feature of this building is its ongoing post-occupancy monitoring strategy for the energy systems.

The main entrance features a sculpture which displays live energy data to students and visitors. This will contribute to a culture of environmental awareness, which is critical. Modifying our individual behaviour will provide some of the biggest carbon savings associated with the buildings we occupy.

29.3 kgCO² /m² - Everyman Theatre by Haworth Tompkins

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The BREEAM Excellent Everyman has impressive responses to the low carbon question. Material recycling is a major feature, with 25,000 19th century bricks and elements from the original timber structure re-used in the new building. In addition, approximately 90 per cent of both demolition and construction waste was recycled. So before the building was even finished, it was racking up an impressive carbon ‘credit’.

The carbon footprint of the concrete structure is mitigated through the use of cement replacements. Natural and exposed finishes are also predominant. Natural ventilation is achieved with the assistance of large brick roof towers (lifespan: 100+ years) which reduce the need for mechanical plant (lifespan: 15-20 years). Energy efficiency in use is achieved through the use of renewables, CHP and air source heat pumps.
You might argue that the cladding above the entrance is a carbon extravagance. However, this is locally appreciated and enjoyed and therefore performs an important social function. The Everyman looks to have a very long low-carbon life.

28.8 kgCO² /m² - Library of Birmingham by Mecanoo architecten

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The BREEAM Excellent Library uses cold water from an aquifer and a CHP as its standout energy efficiency features. It also has a proportion of natural ventilation and stack effect cooling/heating via its interior voids - all good.

Its most striking architectural feature is its cladding, a series of extruded aluminium and curved RHS circular elements covering the facade as part of a unitised cladding system. These features represents a major carbon investment. What are they for? There is no claim they perform a sun-shading role and, if they did, you would expect a different response to each facade. These decorative elements will have carbon-intensive maintenance and replacement costs. Unitised cladding systems are interlocking and quick to assemble, but inflexible and do not lend themselves to localised change. Arguably it is an inappropriate choice for this sort of building. The building is described as having a ‘50-60 year’ design life. Is it acceptable to use resources in such a short-term way in a publicly funded building? What happens to the circles and who pays at the end of 60 years?

18.8 kgCO² /m² - Saw Swee Hock Student Centre, LSE by O’Donnell + Tuomey

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Of the six finalists, the LSE student centre has the lowest emissions and is the only one rated BREEAM Outstanding. The form optimises natural light and contributions to energy efficiency include a CHP, photovoltaics, intelligent controls and natural cross-ventilation. Low embodied carbon strategies such as use of cement replacements have also been deployed.

The architects claim the building is resilient to climate change, an important design attitude. The building has been designed as a long-term carbon investment which can both ‘look after itself’ and be easy to ‘fix’. One example is the south-facing perforated brick screens, which help protect the glazing beneath from sun and rain.

Natural, untreated materials have been extensively used. Large areas of glazing are framed with natural timber and are easy to dismantle, so the building can be maintained over the years using natural materials and low carbon-intensive skills. This is a building that has thought about its future and will most likely be enjoyed in 100+ years time, much like the buildings around it.

25.4 kgCO² /m² - The Shard by Renzo Piano Workshop

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The Shard ‘ticks’ many sustainability boxes, but can a tall building of this type ever be truly sustainable? Rated BREEAM Excellent, the Shard’s principle claims to environmental efficiency are its naturally ventilated double skin facade with adjustable blinds in the central void, and CHP.

Of interest is the relationship between the life of the unitised triple-glazed cladding system and the differing lengths of leases for the various uses: retail, hotel, office and residential. Double-glazed units typically fail after about 40 years. So around 2055 when this building will require re-glazing or re-cladding, how will this relate to lease cycles? By 2050 the UK is meant to have achieved 80 per cent reduction in carbon emissions (vs 1990). How will re-glazing the Shard relate to carbon emissions legislation of the day? This is not looking good.

Buildings of this size and shape have poor net-to-gross and floor-to-wall ratios. In terms of embodied carbon, towers are an inefficient way to enclose space. Tall buildings like this are not part of a low carbon future.

53.6 kgCO² /m² - London Aquatics Centre by Zaha Hadid Architects

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The Aquatics Centre is a prime example of sustainability standards and legislation not delivering a comprehensively low-carbon outcome.
Rated BREEAM Excellent, the building has a genuinely exceptional range of leading-edge sustainability measures. An ‘Innovation’ credit was awarded for use of recycled aggregates and cement replacements. Water use and re-use measures are also impressive. Natural light is abundant, and the building plugs into the Olympic Park’s district heating network.

But the design concept is flawed from a low-carbon perspective because the building contains substantial quantities of steel and concrete. Compare the Aquatics Centre with Hopkins’ Velodrome (also BREEAM Excellent), which uses approximately 1/30th of the weight of structural steel in the superstructure.

Despite the list of sustainability credentials, the building starts life with a massive carbon ‘debt’. It is also worth noting that the annual operational carbon cost per m² is by far the highest of the six, presumably due to the pool. So it is unlikely that this carbon debt will be ‘paid off’.

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