Orchard Grove School harvests Passivhaus Plus rewards

The Orchard Grove Primary School in Taunton is one of a growing number of certified Passivhaus Plus schools in the UK, that generate as much energy as they use. The school was designed in a simple rectangular form and built using prefabricated timber frame, and offers valuable lessons for Passivhaus school delivery.

The £11 million Passivhaus Plus primary school serves the new Orchard Grove housing development on the edge of Taunton. Passivhaus Plus certification means that the school generates as much renewable energy as it uses, in addition to Passivhaus Classic fabric energy efficiency and comfort. To achieve Passivhaus Plus, the project team's strategy was to ensure that energy use was minimal and below the Passivhaus Classic standards. This was achieved through maximising the opportunities through the orientation of the building, eliminating thermal bridging and exemplar airtightness. This meant that the amount of renewable generation of energy required on site was minimised and achievable.

The school was designed by PHT member Stride Treglown with PHT member Jon James Studio Architecture as Passivhaus Consultant, and certified by PHT Patron ZE Passivhaus..

Key stats

Construction: Twin-wall timber frame
Number of pupils: 420 (+ 58 nursery places)
TFA: 2102 m²
Build start date: 2022
Completed: 2023
Certified: Passivhaus Plus, 2025

Orchard Grove Primary School, Taunton. Image credit: Lowfield Timber Frames

If we are to tackle the challenges that climate change will bring, one of the key tasks for the new Somerset Council will be to hardwire energy efficiency into the development of the county. The new Orchard Grove Primary School building is a fantastic instance of how the new council can lead by example."

Sarah Dyke, Executive member for Climate Change, Somerset County Council

Construction

The school was designed in a simple rectangular form, benefiting from an excellent form factor. The structure supported robust airtightness detailing with simplified junctions, and also minimised thermal bridging. The twin-wall closed-panel timber frame system was prefabricated offsite, with a Larsen Truss depth of 360mm. The off-site manufacture helped speed up construction and also minimised risk to the airtightness strategy on site.

Orchard Grove Primary School, Taunton. Image credit: Orchard Grove Primary School

Orchard Grove Primary School, Taunton. Image credit: BAM Construction

To meet the certification, Passivhaus Plus buildings are not only low-energy in use, but they also produce as much energy as occupants consume, turning them into Passivhaus Powerhouses. The energy generated must come from renewable sources and provide enough energy to operate the building throughout the whole year. Orchard Grove is serving the new community in Comeytrowe, and alongside being cheaper to run, it will also provide a healthy environment for staff, pupils and visitors alike, through clean and regulated air flow.

Jon James, Director, Jon James Studio Architecture

U-values

Roof: 0.099 W/m²K

Twin-wall timber frame, with recycled cellulose insulation.

Wall: 0.116 W/m²K

Twin-wall timber frame with mineral wool insulation.

Floor: 0.157 W/m²K

Insulated concrete slab.

Further information can be found at the International Passivhaus Database listing

Building performance

Designed energy performance

Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)

0.4 @ 50 Pa

Space Heating Demand (≤ 15 kWh/m².a)

10 kWh/m².a

Heating Load (≤ 10 W/m²)

9 W/m²

Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)

49 kWh/m².a

Primary Energy Renewable Generation

77 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Services

Heating strategy: An ASHP (air source heat pump) heats the school via radiators, Hot water is provided via direct electricity.
Ventilation strategy: The school is ventilated using an MVHR (mechanical ventilation with heat receovery) system.
Renewables: A solar PV array is specfied for the roof and helps the project achieve the Passivhaus Plus certification for renewable energy supplied. The project comprises 308 PV modules with a total nominal power of 130 kWp and a generation of 77 kWh per m2 footprint area.
Summer comfort strategy: Use of overhangs and boxed deep reveals for the windows and doors reduce the school's overheating potential. The dimensions were tested and adjusted in the PHPP to find the the correct balance. A simple integrated louvre to the window design allows inward opening of windows and therefore secure use out of hours purges to the building as needed.

Orchard Grove Primary School, Taunton. Image credit: BAM Construction

Challenges & lessons learned

Early engagement & collaboration: As always on Passivhaus projects, early and consistent collaboration between the project team is key to successful delivery. The timber frame manufacturer was brought in very early on in the process and worked closely with the project team during pre-construction to align sequencing, load transfers, airtightness interfaces, and M&E strategies. The team shared BIM models and factory drawings to eliminate clashes and refine details before manufacture. This digital-first approach streamlined construction and ensured the project finished on time and within budget. Early engagement and site visits ensured that evidence collection, reviews on key potential issues such as insulating SVP ductwork and solutions to dealing with window brackets, foam glass thresholds etc, was understood and agreed prior to installation.
Form factor: Simple form factor of the building and detailing was key to the building success.
Lessons from previous projects: The project built on the recent Passivhaus certified Frenchay Primary School in south Gloucester with the same team taking lessons learn from that project into Orchard Grove. In particular the change from a traditional concrete ground floor slab with a traditional 'toe' detail was changed to a simple pre-manufactured ground floor insulation detail. This not only removed thermal bridging, but it also sped up site installation significantly. Perhaps the most noticeable difference was the reduction of waste due to the fact that there was no need to cut the insulation on site.
Collating evidence: As is often the case, collating and collecting completed data as required for post completion is a process that can be difficult. The team was able to address this by highlighting this early on and targeting tricky areas such as MVHR/ ASHP commissioning, airtightness test standards and small power use.

Certifier’s view

Notably, this has been one of our smoothest Passivhaus school certifications, with the great collaboration between the project team clearly paying off.

Jesus Menendez, Passivhaus Cerifier, ZE Pssivhaus