How do net zero schools perform in operation?

Little Reddings Primary School in Bushey, Hertfordshire, was one of the first 102 schools in England to benefit from the Department for Education’s (DfE) £20bn school rebuilding programme.

It was procured though the DfE’s 2021 construction framework, using design and construction standards that aim to ensure new school buildings are net zero in operation and more resilient to the effects of climate change. 

The Little Reddings project aligned with the programme’s key criteria, as the existing buildings were identified as having significant condition needs. This led to them being demolished and replaced with a new “net zero in operation” school that incorporates a long list of sustainable design choices and renewable technologies, ranging from a fabric first energy efficient closed panel system to hybrid heat pumps solutions.

The project was completed in June 2025. So how is the school now performing?

Operated by The Bushey St James Trust, Little Reddings was a direct replacement for the previous school in terms of pupil numbers. It is a two-form entry primary school, with capacity for 459 students, 420 within the primary school and 39 within a nursery.   

Dave Wood MCIOB, DfE Director at Morgan Sindall Construction, says: “Little Reddings represents the culmination of years of collaborative work and development with industry experts and the DfE to ensure that schools delivered under its new programme meet the framework’s ambitious but essential principles for sustainability and building quality.

“This has included refining decarbonisation strategies with regards to pre- and onsite activity as well as ongoing building performance. A lot of these lessons were captured during DfE pilot schemes, which helped to formulate the specification standards for new school buildings.”

These pilot projects included Newhouse Academy in Rochdale and Scunthorpe’s Trent View College, as well as the sharing of lessons learnt from projects procured by other means such as Hertfordshire’s Buntingford First School, also built by Morgan Sindall, which is the country’s first carbon neutral school. 

“Pooling this knowledge with the DfE and their technical advisors, the school at Little Reddings has delivered results that are even better than we’d originally hoped for,” says Wood.

To allow the school to continue operating during the project, it was split into two phases. During the first phase, a new two-storey building was constructed on the site of the school’s playing fields. It consists of 14 classrooms, a hall, studio, practical room, and a dedicated special educational needs space.

The new school has been designed to accommodate the same number of pupils across a more efficient building footprint, reducing the area of school that would need to be operated and maintained from 2,750m², to 2,380m².

Once the construction work was complete and the new school building operational, the second phase saw the demolition of the two existing buildings. A multi-use games area (MUGA) and full-sized Sport England sports pitch were created on the land which previously contained the old buildings.

As the school was still operating throughout the development, Morgan Sindall had to keep tight control of all onsite activity. Deliveries were scheduled to minimise disruption and to avoid the period just before the start and after the end of the school day to avoid disrupting parents collecting their children.

Noise levels also had to be tightly controlled. The team had to strike a balance between not disturbing classes in the middle of the day and not undertaking noisier work early in the morning or late evenings which would disturb residents.

The building was created using an offsite-manufactured closed-panel composite timber frame system. Created by Streif and precision-engineered at their manufacturing plant, it has very high levels of pre-manufactured value, so produces zero waste on site.

The system delivers excellent sound insulation (up to 80 dB) reducing the potential for noise disturbance between adjoining classrooms and it also has a fire resistance of REI 60 minutes or longer.

The drawings produced by the project’s architects at ATPA were used to create standardised modules made with recycled and renewably produced materials, minimising the use of carbon-hungry components like steel and cement.

Once produced at the plant, the wall panels and heavy-duty floor cassette system was packaged and arranged for transportation in a specific order. This ensured they would arrive on site pre-organised for assembly, making it as simple as possible and minimising carbon production from vehicles during construction.

Robert Addison MCIOB, senior project manager at Morgan Sindall, says: “We’ve used this type of system for projects in the past and always been impressed by the accuracy of the panels. The way the system is packaged and transported makes the whole assembly process very streamlined.”

In addition to floor and wall panels, the system also incorporates factory fitted sub-assemblies such as windows and doors, which together build into standardised modules.

The walls of the building, which were clad with traditional brickwork on the ground floor and rendered on the first floor, were designed to deliver an air tightness level of 3 m3/h.m2@50pa to avoid air leakage and reduce uncontrolled air flow. This was delivered by a high performance Isover Vario KM Duplex membrane, which is three times stronger than standard polythene membranes and inherently breathable, so any trapped moisture can escape from the building. Following completion, the building was proven to have beaten its air flow target and achieved a rate of 2.38 m3/h.m2@50pa.

The building was fitted with a bio-solar roof with 270 photovoltaic (PV) panels to reduce the school’s reliance on grid energy whilst also supporting biodiversity.

A hybrid heat pump system was installed, that used ground source heat pumps for the heating and air source heat pumps for the hot water. This combination allows the school to get the best from both systems while reducing heating costs and the building’s reliance on fossil fuels.

To create this, twelve bore holes for the GSHPs had to be located underneath the new sports pitch at a depth of 150m.

“This required the careful coordination of a number of subcontractors to ensure that the bore holes and the position of other services wouldn’t be at similar depths and inadvertently clash, which would affect the site’s drainage system,” says Addison.

Wood adds: “Much of the insights that went into planning Little Reddings were powered by new digital capabilities and research.”

A key part of this was circular and regenerative twin research projects that “allowed us to use digital models to compare different approaches in order to identify the most efficient, carbon reduction methods,” explains Wood.

To measure the performance of Little Reddings carbon production, Morgan Sindall used the digital carbon assessment tool CarboniCa, which measures the carbon emissions during a buildings design, construction, and lifecycle. The embodied carbon for the new Little Reddings school was just 585.4kg of CO² per metre square; the RIBA (Royal Institute of British Architects) target is 1,000kg.

Wood says that “the CarboniCa analysis allows stakeholders to have a really granular understanding of the carbon created by the building’s construction and ongoing operations”. This includes identifying that the building’s foundations were the largest single contributor, accounting for 28.5% of lifecycle embodied carbon. The ceiling and floor finishes were the next highest, representing 17.0% and 14.6%, however the school’s structural frame contributed just 7.3% to the total.

The school’s performance over the first year of being in operation was tracked using a post occupancy evaluation (POE) reporting process. This measures how the school performs in real life with regards to energy consumption throughout the year.

The target for the school’s ongoing energy consumption was 52 kilowatt-hours per square meter, as mandated through the DfE’s design brief and technical annexes, which was reduced to a designed 48.56 kilowatt-hours per square meter during the RIBA stage 4 design process. The POE report showed that the school building is achieving a much lower performance of 41.44 kilowatt-hours per square meter.

The report also gives recommendations for ongoing improvement. For example, it noted that about 34 MWh of energy usage occurred outside of normal school hours. It also identified specific classrooms that were comparatively underperforming and the human factors as to why that might be.

“This level of information empowers the school with actionable insights that mean Little Reddings could achieve even more impressive levels of efficiency moving forward,” Addison says.

Wood says: “Little Reddings provides a masterclass in how to create a high-end educational environment that goes above and beyond when it comes to quality of delivery, cutting carbon and providing communities with sustainable facilities for the long-term.

“To ensure the lessons learnt from this project are captured and deployed moving forward, we conducted a workshop with the DfE and their technical standards team to inform best practice on future school developments and Spec25, the updated specification requirements.”

Following completion and the new school’s doors opening for the first time, Josh MacAlister, minister for children and families, commented that “it is fantastic to see pupils at Little Reddings Primary School are now learning in a school that is not only fit for the future, but somewhere that they can feel proud of and want to learn in every day”.