Pollution-busting London Dock secondary school

The Passivhaus certified Mulberry Academy secondary school has been designed in a busy and compact urban location in the Docklands area of London.

The school is situated moments away from Tower Bridge, the Tower of London, St Katharine Docks and the City. Passivhaus was chosen for the project to counter the problems of air pollution, thanks to the excellent indoor air quality it offers.The improved airtightness, and use of MVHR to draw in fresh air from 5 storeys above ground was essential for this. Passivhaus also helped address the acoustic concerns from the road. The architectural and landscaping design has created considerable green space with extensive facilities for sports and leisure, which will be open for community use.

Key stats

Construction: Post-tensioned concrete frame, with elements of steel and timber frame
Number of pupils: 1181
Treated floor area: 8,661 m²
GIA: 12,280 m²
Form factor: 1.53
Build start date: 2020
Completed: 2024
Certified: Passivhaus, 2025

Entrance, Mulberry Academy London Docks. Image credit: Tim Pestridge-

The Passivhaus design also delivers particular benefits for air quality, with fresh filtered air, creating a natural defence against the nearby traffic. The complex site challenges, with an original dock wall and basement build on a busy road, demonstrate that Passivhaus and low carbon design can be achieved on the most challenging of urban sites. This is vital in the race to net zero.

Rory Martin, Senior Architect, Architype

Construction

The design achieves a low form factor of 1.53 largely by requirement of the compact and constrained site.

Mulberry Academy London Dock - Sketch view from NE. Conceptual early stage massing diagrams. Image credit: Architype

Mulberry Academy London Dock - Sketch view from SE. Conceptual early stage massing diagrams. Image credit: Architype

Roughly a quarter of the building fabric is below ground and used to accommodate large halls required by a modern secondary school. To maintain natural light each hall is half below ground and half above ground, providing windows at high level within the space.

The good form factor allowed thermal performance to be relaxed and created unusually high allowance for thermal bridges in a Passivhaus. The school has 548 W/K thermal bridges, or 14% of the transmission heat losses. One such thermal bridge is illustrated below and was to support a trellis that supports plant growth up the stair cores.

Mulberry Academy London Dock - Terrace with trellis in the background with planting begin to grow up.. Image credit: Jack Hobhouse

Mulberry Academy London Dock - Thermal bridge analysis of trellis spigot. Image credit Architype

Sequencing

Embodied carbon

Value engineering changes to incorporate post tensioning concrete helped to significantly reduce embodied carbon. The typical floor slab reduced from 300mm reinforced concrete to 225mm post-tensioned concrete which significantly reduced the weight of structure and size of foundations required. The project also sought to minimise embodied carbon by maximising cement replacements, and specifying concrete strength at 56 days rather than 28.

U-values

Roof: 0.151 W/m²K

PIR roof system.

Wall: 0.196 W/m²K (average)

Various wall types:

In situ concrete with XPS insulation below ground.
Precast concrete with mineral wool, blockwork and parge coat.
Brick with mineral wool and SFS zone or in situ concrete.
Rainscreen with mineralwool and SFS zone or in situ concrete.

Floor: 0.089 W/m²K (if including the ground reduction factor in PHPP). 0.372 W/m²K (if not including the ground correction factor).

Concrete slab with XPS insulation.

Mulberry Academy London Dock Aerial view showing the accessible roof terraces. Photographer: Jack Hobhouse

Building performance

Designed energy performance

Airtightness (ACH @ 50 Pa)	0.2 ACH @ 50 Pa
Space Heating Demand (≤ 15 kWh/m².a)	12 kWh/m².a
Heating Load (≤ 10 Wm²)	8 W/m²
Primary Energy Demand (≤ 85 kWh/m².a)	76 kWh/m².a

Services

Centralised mechanical ventilation with heat recovery (MVHR) systems were specified. The ventilation system has demand supply controlled by temperature and CO₂ sensors in classrooms. In addition the MVHRs provide peak lop cooling when required to support future climate resilience.
Air source heat pumps (ASHP) provide heating and hot water. Brise soleil shading is used above some of the school's glazing to provide summer shading.

Challenges & lessons learned

Mulberry Academy London Dock - Ground floor student entrance. Photographer: Jack Hobhouse

The site has a number of significant challenges:

The school was built on a dense urban site in central London. The compact space necessitated a large basement and substructure.
The footprint of the site was significantly smaller than is normal for a secondary school of this size, which required the entire site to be utilised creatively. Strategies included the design of hall spaces below ground, 6 storeys of building above ground, outdoor and play spaces on the various roof terraces, and biodiversity growing on some facades of the building.

The road immediately to the north of the site is a major source of air and acoustic pollution; issues that Passivhaus significantly helped to address. Creating a sense of connection to biodiversity and nature for students in this context was a particular challenge.

The project team had to work hard to deal with significant thermal bridges necessitated for the delivery of rooftop recreation and garden spaces, as well as vertical support for plants on facades and an extensive basement.

The school achieved an exceptional airtightness performance of 0.2 ACH @ 50pa, or 0.63 m3/hr/m2 @50pa on building with a complex façade and large areas of curtain walling at the ground floor. The prototype testing method and quality assurance methods from the project are to be taken forwards for future Passivhaus schemes.

Conceptual early stage landscape section. Mulberry Academy London Dock. Image credit BD Landscape

Architect’s view

The new Mulberry Academy London Docks School stands as a striking civic landmark, respecting the area’s rich history and architectural character. Creatively utilising space, the six-storey above ground building features terraces that create vibrant outdoor areas. A thoughtfully designed landscape strategy prioritizes ecology and wellness, integrating vibrant green spaces on terraces and façades to enhance student and community well-being. Internally, the innovative design continues with halls and multi-use games areas positioned at ground level and one level below, ensuring natural light and visual connectivity. Teaching and learning spaces occupy the upper floors, where generous glazing strengthens the connection to the outdoors.

Passivhaus was implemented to address air quality and noise challenges from the adjacent road while ensuring high construction standards. Enhanced airtightness, combined with fresh air drawn from high levels, creates a consistently comfortable and healthy environment for all users.Through its creative and sustainable design, Mulberry Academy London Docks provides an enriching space that not only supports academic excellence but also nurtures well-being, engagement, and a sense of belonging within the community.

Hugh Pearce, Architect & Passivhaus Lead, Architype

Mulberry Academy London Docks, South Elevation. Photographer: Tim Pestridge

This flagship Passivhaus school in London creates a low carbon building and a healthy environment for the students, teachers and local community.This school builds on Kier’s experience working on Passivhaus projects, having delivered seven for communities across the UK.

David Rowsell, Managing Director, Kier Construction London