An airtightness exemplar; update on the construction of a new Passivhaus primary school in Wolverhampton

Simon Butler, Managing Director – Building Central at Tilbury Douglas, provides an update on the construction of a new Passivhaus primary school, Wednesfield Technology Primary School.

We are currently on-site, delivering our fifth school for Shireland Collegiate Multi Academy Trust (SCMAT), this time on behalf of the Department for Education (DfE). Bringing lessons learned from a well-rehearsed design team, this project will be a special one, incorporating SCMAT design principles with Passivhaus Classic standards. Early air tests show that we are well ahead of the standards requirements, a credit to the whole team.

Located in Wolverhampton, the brownfield site was once home to Edward the Elder School but had stood derelict for several years, creating a void in this otherwise busy part of town. The new school, selected to be part of the highly successful SCMAT will be a new jewel in this town’s urban landscape, accommodating nearly 450 new primary school places.

The ‘Technology’ status of the school brings a fresh approach to education, incorporating principles of ‘flipped’ learning, family supported learning, and technology-for-feedback.

Meeting client expectations

Meeting the City of Wolverhampton Council’s objectives to improve air-quality in schools and reduce energy usage, the Passivhaus Classic design guarantees building performance, while specifying a range of sustainable, low embodied carbon materials.

Following the demolition of the existing school, the design solution proposed a single block, two-storey new build, catering for two-form entry space requirements. The scope also included external refurbishment to the Grade II listed caretaker’s lodge on the site.

The architectural design, led by local architects Corstorphine + Wright (C+W), references the local residential vernacular of red-brick and rendered facades, weaving in unification of the SCMAT common design language.

Retaining most of the trees on the site was of key importance in the brief, so the positioning of the school was dictated by this, as well as the requirement for a sports pitch and hard play area.

Construction update

Once demolition was completed, we recycled the crushed materials to form the sub-base for the new school. Also helping to meet the low-carbon brief, a timber frame solution, developed with structural engineers, Clancy Consulting, has since been fireproofed and erected.

The building is now watertight, (which was fortunate given the extreme weather conditions in January) with the roof membrane and windows now having been installed. Brickwork and external doors have also progressed, and external fencing is being erected.

The external blacktop carpark basecourse has been laid and external services installed to the boundary, ready to be connected.

Internal works are progressing to first fix, M&E, closing-off the partitions and taping. We will then be moving into decorations, joinery, and ceilings. Final fix items will follow along with floor finishes.

This progress enabled us to have our first airtightness test in January and we were delighted with the results, which exceeded the Passivhaus standard by over 100%! Air changes per hour are required to be 0.6ACH @50 pascals, with this project averaging 0.225ACH @50 pascals. Furthermore, the air permeability requirement is 0.93m3/hm2 and our project achieved 0.33m3/hm2.

Doing things differently

Passivhaus promotes a whole-building approach with measured targets, focused on high-quality construction, certified through an exacting quality assurance process.

The process requires extensive photographic and quality inspections of all elements of the building programme, which is shared with the Passivhaus consultants and independently inspected on site.

Getting the project right at design stage was fundamental, and at this point eliminating thermal bridging was a key priority. With C+W we used Revit to model our details, simplifying and then standardising these across the building.

The Passivhaus brief has been the catalyst for a variety of alternative approaches on site. Our team received specialised training to introduce them to Passivhaus risks and how best to support our trades in delivering the strict standards. We have also received ongoing support from our Passivhaus consultant, Delta Q.

We insulated the building slab with almost double that of a normal school project, installing two layers of insulation with staggered joints to prevent heat loss. Tolerances are ‘to the millimetre,’ which meant each sheet of insulation was cut with a hot wire cutter for perfect alignment and to prevent gaps. The raft slab incorporates an unusual ‘toe’ detail, so that the insulation beneath the building extends all the way beneath and around the slab.

We developed a prefabricated Larsen Truss system for internal walling, offering 360mm of insulation, while supporting the cold bridging strategy. To avoid compromising the airtight line, the timber panels have been fixed together from the inside. Although a slower process, this is best practice for achieving airtightness.

The building will be heated and ventilated using a combination of natural and mechanical ventilation with heat recovery. MEP is delivered by Dodd Group.

Engaging with the community and creating opportunities

Taking advantage of the site’s prominent roadside frontage, we have designed engaging posters to inform the community about this forward-thinking development. Information includes school pedagogy; who our team are and how they entered construction; as well as the development’s sustainable credentials and how this will benefit users.

As is always important on Tilbury Douglas projects, the delivery of Wednesfield Technology provides an excellent training ground for budding colleagues.

Apprentices Caitlin Walsh and Dan Floyd and Graduate Engineer Jack Bennett have gained valuable learning experiences from helping our core team to deliver this project. We have also accommodated T-level student Shay Doyle from Dudley College for his nine-week placement.

Reaching out into the wider community, our Social Value Manager Charlotte Davies has been supporting West Bromwich Collegiate Academy (another SCMAT school delivered by Tilbury Douglas) with its careers fair, providing STEM careers support to secondary school pupils.

As part of Tilbury Douglas Winter Wishes campaign, our site team and supply chain members kindly donated raffle prices to Wallbrook Primary Academy, a neighbouring school in support of its annual Christmas Fair.

We will also be holding our Build UK Open Doors tours on the 19 and 21 March 2024.

Feedback so far

Our first CCS visit provided us with great feedback:

“An excellent visit, with the team fully committed to the aims of the Scheme. Community concerns have been well addressed and responded to and promotion of the industry is exemplary. Environmental controls are robust, and the workforce informed of the measures taken. Tilbury Douglas is fully committed to NetZero and staff are aware of the part they must play, through training, data collection and KPI targets.”

Looking ahead

We are looking forward to continuing to work collaboratively to deliver this new school in late spring 2024, which will greatly increase the education provision in the region.