Harris Academy Sutton (Passivhaus)

Following the successful delivery of the UK’s largest non-residential Passivhaus scheme, the George Davies Centre for the University of Leicester, our team were appointed by the London Borough of Sutton to deliver the same ultra-high energy efficient standard for the new Sutton secondary school.

Read our top tips for creating Passivhaus property

The trailblazing building for Harris Academy Sutton in South London takes sustainability to new heights. As the first secondary school in the UK to be built to the Passivhaus standard and the largest Passivhaus school in the country, the top-quality building sets the sector standard for exceptionally low energy use and superb user comfort.

The four-storey, six-form entry school accommodates 1,275 pupils and 95 staff.

The school forms part of Sutton’s masterplan for the London Cancer Hub – a major project to create a world-leading life-science campus for research, treatment, education and enterprise. A collaboration between The Institute of Cancer Research and Sutton Council, this park is dedicated to research to cure cancer, with Harris Foundation appointed as the Free School education provider.

Fusing learning with life science hub ambition

The Harris Academy Sutton is the first scheme to complete on the site and will have a special focus on the science disciplines, with the objective of inspiring the scientists of the future. It integrates secondary school pupils into the campus’s wider remit of scientific research and treatment to inspire pupils to forge a career within life sciences.

Why Passivhaus?

Developed in Germany in the early 1990s, Passivhaus is an international standard for designing and constructing buildings that deliver super-high energy efficiency and impressive occupier comfort. Crucially, to achieve certification, everything must be built and completed exactly as designed and to top quality standards, ensuring that building performance in use mirrors the design model and targets.

Sutton Council has had a forward-thinking approach to sustainability for decades and its ambition was for a school with minimal operational carbon, certainty of energy savings and an excellent indoor environment. The council opted for a Passivhaus building because of its ability to meet these objectives in a more focused way than a BREEAM scheme.

For the school, this translates into energy consumption that's typically 80% lower than a standard new building, giving tremendous savings on operating costs and carbon emissions.

Internally, better air quality, ideal thermal temperature and the right amount of natural light provide an optimum building to study and work in. Throughout the year, mechanical ventilation (with heat recovery) provides fresh air, with the quantity locally adjusted in response to CO2 level sensors in all the rooms. In the winter, fresh warm air heats rooms and spaces. They never get stuffy, which tends to cause sleepiness, and there are no uncomfortable draughts or cold spots. In the summer, the building stays fresh and cool. As a result, pupils and staff feel alert and comfortable all year round, which positively impacts learning ability, wellbeing and teaching quality.

Fabric first

The Passivhaus ‘fabric first’ approach to design and construction is about carefully optimising the fabric of the building itself so that energy efficiency is achieved passively.

It centres on measures such as extra thick insulation in walls, floors and roof; triple glazing on windows and doors; and an exceptionally airtight building envelope – approximately 14 times more airtight than building regulations require. Through exceptional insulation and air tightness, heat leakage through the windows, walls, floor and roof is prevented.

Other fabric elements include careful orientation and sizing of windows together with selective shading to optimise solar gains in winter and prevent overheating in summer.

Passivhaus explained in 90 seconds

Complex construction

Passivhaus buildings have more high-performance elements and the specification for mechanical and electrical components requires better products. In addition, contractors need to be extremely diligent to ensure the top quality workmanship and installation that the standard requires.

With quality critical to achieving certification, we engaged with the supply chain at a very early stage to communicate its significance, and continually reinforced the importance of getting things absolutely right.

Graham Thompson at Willmott Dixon explains:

“A key part of this was a Passivhaus-specific induction for the entire supply chain. Every person was made aware of the concept, why getting everything right was so important and why stringent quality control was essential.”

To support this, an open, 'no blame' culture was established, with everyone encouraged to speak up if they thought something was being done wrong. These messages were strengthened by toolbox talks throughout the project and by having posters on constant display.

Very high levels of insulation are integral to Passivhaus. Where insulation boards abut there must be no gap, additionally the tolerance (air gap) behind and between can be no bigger than 3mm so quality needs to be outstanding. For example, the school's ground floor, set on concrete slabs, and CLT roof both required perfectly abutted insulation boards that met these extremely tight gap tolerances, through multiple layers with staggered joints. On the timber-framed second and third storeys, insulation was pumped into the wall void to completely fill it.

Achieving airtightness is a huge challenge on a Passivhaus building and it can't be left until the end of a project. Every single interface needs to be completed efficiently and to high quality standards, every inch of the airtightness membrane needs to be checked, and checks and tests must to be carried out continually.

On a Passivhaus building, the requirement is for very low air leakage rates, with no more than 0.6 air changes per hour. For conventional buildings, the air change requirement under building regulations is around 10.0 m3/h.m2 and for a BREEAM building, it's 4.0. Willmott Dixon achieved 0.30 air changes per hour on the school (equivalent to 0.7 m3/h.m2), which for a building of over 10,000 square metres is remarkable.

A template for future schools

For Sutton Council, the new £38m school is a major asset in every respect. It is being perceived as a gateway for the London Cancer Hub, which is set to deliver economic regeneration through education, employment and training.

For pupils and staff, the superb air quality and optimum temperature provide a healthy, productive environment, supporting better learning and wellbeing. As part of the London Cancer Hub, the school integrates pupils into the campus’s wider remit of scientific research and treatment, encouraging careers within life sciences.

Completed in July 2019, with the first intake of pupils in September 2019, this remarkable school sets standards and ambition for sustainability and quality and is an inspiring beacon for future secondary schools to follow.

Key outcomes

• The UK's first Passivhaus secondary school
• The country's largest Passivhaus school
• Very low operating costs
• Very low carbon footprint
• 80% less energy use than a conventional building
• Ideal internal temperature all year round
• Superb air quality for better learning, health and wellbeing
• Exceptional airtightness – around 14 times lower than building regulations
• 0.30 air changes per hour - half the Passivhaus 0.6 requirement
• 40% project spend with local business