Passivhaus school first for Bedfordshire
A new teaching block for Thornhill Primary School is the first in Central Bedfordshire built to the Passivhaus standard and is also the first certified Passivhaus school for the architect, MEP engineer & main contractor.
Central Bedfordshire Council commissioned the newbuild building to help accommodate the growing needs for school places in the area, with the school increasing its capacity from 210 pupils to 630, plus nursery places. The project is intended to set a precedent for robust low energy and sustainability standards to inform the local authority’s future projects.
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ECD Architects introduced the concept of designing and building to the Passivhaus Standard at RIBA stage 1. This was received positively by Central Bedfordshire who instructed us to target certification to benefit from the health and well-being benefits of improved thermal comfort and air quality, as well as to reduce financial running costs.
Gary Alston, Design and Technical Director, ECD Architects
Key stats
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Choosing Passivhaus
Passivhaus was selected to ensure the new building’s quality of construction, while also providing significant benefits to the whole life cycle cost, a reduction in its financial running costs when compared with standard UK Building Regulations and improving thermal comfort and indoor air quality.
In pre-application discussions between the project's architects, PHT member ECD Architects, and Central Bedfordshire Council's Sustainability Officer, the Passivhaus standard was agreed to replace BREEAM as the building's environmental goal - a recognition that Passivhaus, as a more focused and specific target, is much more stringent in terms of building energy performance. However, BREEAM targets concerning water usage and management were retained.
Cost analysis carried out during Stage 4 by the cost consultant illustrated that the cost for Passivhaus represented 5.4% of the total construction costs (including overhead profits and preliminaries).
Embodied carbon
The building was constructed in Cross Laminated Timber & Glulam, using offsite manufacture, to keep embodied carbon emissions low. The project also aimed to follow the principles of the Circular Economy - striving to lock in and retain the value of materials used within a building, and using the built asset as a material bank during its operation, to be unlocked at the end of its usable life.
Design
As the scheme was developed from a pre-approved outline planning permission, orientation and outlook of the building were already fixed.
The building design incorporates a deck wrapping the entire two-storey section of the building, providing valuable breakout space for smaller group learning, connecting teaching with the outside. The building also includes a double-height entrance atrium and split-level library, adjacent to the new sports/ dining hall.
A comprehensive shading strategy was implemented, including: roof overhang to East & West elevations; a brise-soleil (serving first floor classrooms) and first floor walkway (serving ground floor classrooms) to South elevation; and an external fabric canopy serving the South elevation
We cannot wait to open up this outstanding space for students at Thornhill in September. Its forward-thinking design will allow us immeasurable opportunities for furthering the children’s awareness around environmental innovations, enriching their educational aspirations and providing boundless benefits to our growing community for future generations.
Claire Bryan, Co-Chair of Thornhill Primary School Governors
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Wall Brick finish: Brick, air cavity, low thermal conductivity brick ties, rigid insulation, airtightness membrane, CLT panel, timber battens, plasterboard U value: 0.07 W/m2K Zinc finish: Zinc, plywood, air cavity, thermally broken helping hand brackets, rock fibre insulation, airtightness membrane, CLT panel, timber battens, plasterboard U value:0.13-0.14 W/m2K |
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Floor Screed, reinforced concrete slab, DPM, closed cell insulation U value: 0.11 W/m2K |
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Roof Zinc finish: Zinc, plywood, rigid insulation, airtightness membrane, CLT panel U value: 0.06-0.07 W/m2K Felt finish: Felt, plywood, rigid insulation, airtightness membrane, CLT panel U value: 0.11 W/m2K |
Measured energy performance
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Airtightness (≤0.6ACH@50pascals) |
0.42 @50pascals |
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Thermal Energy Demand (≤15kWh/m².yr) |
15 kWh/m².yr |
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Thermal Energy Load (≤10W/m²) |
12 W/m² |
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Primary Energy Demand (≤120kWh/m².yr) |
126 kWh/m².yr |
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Primary Energy Renewable Demand |
85 kWh/m².yr |
Lessons learned
- The material specification was key to the success of the project, for both the building construction and services, and ensured the Passivhaus principles were achieved. Tried and tested products were used backed up with advice from manufacturers and product suppliers.
- Working with a collaborative, pro-active contractor with high quality management monitoring standards and a willingness to learn and adopt the required skills, through on-site Toolbox Talks, ensured a compliant building was achieved.
We are delighted to have completed this ground-breaking project, delivering an outstanding educational facility that has achieved the very highest of sustainability credentials, and has been recognised by the Passivhaus Institute as a fully certified building.
Andrew Morris, Business Development Director, Ashe Construction
Key team
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We are very excited that the pupils & staff of Thornhill Primary will gain the benefits of this new building when they return in September. Better air quality and thermal comfort, and improved well-being, with reduced running costs; it is no surprise that more councils and education bodies are choosing to build to the Passivhaus standard and with CLT to provide exemplar learning environments like Thornhill for future generations to benefit from.
John Heaney MCIAT, Senior Architectural Technologist, ECD Architects
Further information
Thornhill Primary School Expansion
Work completes on new Thornhill Primary School building
Previous PHT story: New Passivhaus primary in the pipeline - 16 December 2019
Passivhaus Educational Buildings Case Studies
Passivhaus for Educational Buildings Campaign
PHT guidance: Qualiity Assurance for large & complex buildings
14th September 2022
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