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Harris Academy Sutton

Location: Sutton, London
Completion Status: Completed Occupancy: September 2019
Architect: Architype Consultant: Architype
Contractor: Willmott Dixon Client: London Borough of Sutton
Certification: December 2021 Certifier: WARM
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The pioneering Harris Academy Sutton is the UK’s first Passivhaus secondary school and the largest Passivhaus school in the UK (Feb 2022).

Harris Academy Sutton. Image credit: Jack Hobhouse

Sutton Council commissioned the Harris Academy Secondary school, to provide an optimal learning environment for 1275 students between the ages of 11-18 and as part of its One Planet Sutton vision. The Council’s 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.

As a collaborative team we’ve overcome the significant technical challenges of delivering Passivhaus design and quality at this scale to create the UK’s first Passivhaus secondary school and the UK’s largest Passivhaus school. 

Building on insight from our previous Passivhaus buildings we have delivered a low carbon timber-framed school that offers students and staff excellent light and air quality, non-toxic materials, lower energy bills and a beautiful and inspiring building that connects to its suburban setting. Taking a Passivhaus approach means we know the building will achieve significant savings on operating costs and carbon emissions. 

Christian Dimbleby Lead Project Architect, Architype

Harris Academy. Image credit: Jack Hobhouse

Key stats

Occupancy: 1275 pupils & 95 staff

Construction costs: £38 million

Construction:  Concrete frame & CLT

Gross Internal Area: 10,600 m2

Treated Floor Area: 8,953 m2

Form factor: 1.8

Harris Academy. Image credit: Jack Hobhouse



The building is designed to provide flexible space for the school’s growth, with classrooms, sports and teaching accommodation spanning over four storeys, including 11 laboratories to suit the school’s science aspirations. To reduce the height impact of the building, a concrete half frame was sunk into the ground. For the upper storeys, Cross Laminated Timber (CLT) was specified for its non-toxic and structural qualities. Douglas fir timber, brick and copper were used as cladding. 

The school is also optimally orientated, the result of extensive daylight, overheating, noise and ecology surveys. Careful orientation and sizing of windows together with selective shading, including brise-soleil on south facades.and vertical fins on east & west facades, help optimise solar gains in winter and prevent overheating in summer.

Harris Academy Sutton. Image credit: Jack Hobhouse



Harris Academy construction. Image credit: Willmott DixonThe CLT roof is made up of carefully abutted insulation boards to increase airtightness levels. Where insulation boards abut it was important that there must be no gap, additionally the tolerance (air gap) behind and between can be no bigger than 3mm so the quality of installation needed to be outstanding.

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.

To achieve the airtightness levels required, checks and tests on the airtightness barriers needed to be carried out almost continually during construction. The projects achieved an airtightness result of 0.30 ACH @ 50 Pa, half the Passivhaus requirement of 0.6 ACH @ 50 Pa.

Watch the video below from KLH of the construction.


Construction sequencing at Harris Academy Sutton. Credit: Willmott Dixon

Douglas fir timber cladding
Magnesium oxide sheathing board
195mm I-joist fully filled with blown cellulose fibre insulation
240mm glulam structure with timber frame infill

U value: 0.21 W/m2K (average) 

Wall build up. Image credit: Yogini Patel

100mm XPS insulation
200mm reinforced concrete slab

U value: 0.71 W/m2K (excl. ground correction factor)

U value: 0.16 W/m2K (incl. ground correction factor)

250/300mm CLT with PIR & EPS insulation

U value: 0.12 W/m2K (average)


Energy performance 

Airtightness (≤0.6ACH@50pascals)  


Thermal Energy Demand (≤15kWh/m².yr)

15 kWh/m².yr  

Thermal Energy Load (≤10W/m²)


Primary Energy Demand (≤120kWh/m².yr)



Each room is served with a very small domestic scale radiator and light sensors to help students and teachers know how to use the room’s minimal light and heating most efficiently. Two small 150 kW boilers supply all the radiator heating in the 10,600 m2 building.

Adopting Passivhaus has enabled the school to save approximately 80% on heating bills, significantly reducing the school’s environmental impact. 


Harris Academy. Image credit: Jack Hobhouse


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.

Willmott Dixon, Main Contractor

Lessons Learned

The project team’s biggest lessons learned were about managing such a large-scale and complex project.

Design phase

  • The project aimed to demonstrate a ‘one-team ethos’ from start to finish, collaborating with the client, contractor and sub-contractors to ensure that ambitious environmental standards were met.

  • A contractual agreement was drawn up that includes involvement of the contractor and their supply chain at early stages for design input and collaboration on buildability.

  • The design team needed to have a willingness to interrogate standard design defaults to optimize building fabric, structural and MEP strategies.

  • It was important to ensure that the design was completed as much as possible before construction commenced.

  • Construction sequencing was optimised to minimise changeover of trades. It was found that design with the least changeover was often the easiest to install.

  • As a school with a high primary energy demand, the team ensured appliances were as low energy as possible through coordination between MEP, FF&E and end-user client.


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.

Graham Thompson, Willmott Dixon

Harris Academy construction. Image credit: Willmott Dixon

On site

  • The key contractor Willmott Dixon had a key group of site managers who had undergone the Certified Passivhaus tradesperson training.  There were also several on-site Passivhaus Champions to check quality control.

  • Almost all the subcontractors on the project had never worked on delivering a Passivhaus. Willmott Dixon made it mandatory for all key trades personnel to undergo a pre-construction Passivhaus induction and guarantee that at least 2 people from each company who attended this course would be available on-site.

  • Regular Passivhaus-related tool-box talks were also conducted for site personnel.

  • The design team ensured details were clear for every junction/ penetration for airtightness. Colour-coded 3D drawings with accompanying notes were used.

  • Quality check processes were programmed in, including the integration of Passivhaus QA into existing QA processes

  • Early construction mock-ups were created off-site, which also helped with developing sequencing.

  • Interim sectional airtightness testing helped address any quality or performance issues at an early first installation stage. Tests were conducted again at a later stage on larger sections.

  • Any possible changes on site, including value engineering changes, were run through the Passivhaus design team to check there was no significant Passivhaus impact.

  • A flying factory for prefabrication was used on site to precision manufacture all the timber components.  Prefabrication helped speed up activities and maintain quality for Passivhaus requirements.

  • An open, 'no blame' culture was established, with everyone encouraged to speak up if they thought something was being done wrong. Emphasis was placed on expectations of quality instead.


Sutton Secondary School - Testing ©WARM/ Architype


There is a growing array of Passivhaus Educational Buildings and next-level energy-efficieny architecture in the UK. Harris Academy is included in the new SDF Alliance Exemplars Library amongst several other Passivhaus projects. Demonstrating a holistic approach to sustainable building, the collection of case studies forms part of the mission to drive net-zero in construction in the UK.


Key team

Client: London Borough of Sutton

Architect & Passivhaus Designer: Architype

Main Contractor: Willmott Dixon

QS: Synergy

Planning Consultant: Lichfields

Structural Engineer: Price & Myers

Acoustic & M&E consultant:  BDP

Landscape: Churchman Landscape Architects

Fire Consultant: Arup

Education Consultant: Lloyd Wilson Partnership

Passivhaus CertifierWARM 

Sutton Secondary School - proposed massing ©Architype

Unless otherwise stated, all images © Jack Hobhouse


Further information

Harris Academy Sutton 

Previous PHT article: Harris Academy Sutton: beacon for high-performance school design 6 October 2021

Previous PHT article: Passivhaus massivhaus: child's play at Sutton Secondary 29 February 2019

Passivhaus for Educational Buildings Campaign

Passivhaus Schools & Educational Buildings

Passivhaus Qualiity Assurance for large & complex buildings

Willmott Dixon: Harris Academy Sutton

Passive House Plus: Inside the UK's Largest Passivhaus School - Issue 36

Architect's Journal: Massivhaus: Harris Academy Sutton by Architype22 November 2019

SDF Alliance Exemplars Library



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