Pen Y Dre High School

A first for Wales

This trailblazing pathfinder project to retrofit the 1970s-built Pen Y Dre High School in Merthyr Tydfil is destined to be Wales’ first school retrofit to net zero carbon in operation with a 20% reduction in embodied energy.

Pen Y Dre High School is a comprehensive for pupils aged between 11-16 years old. Built in 1972, its interconnected buildings include an indoor swimming pool, sports hall and gymnasium.

Lawray was appointed by Morgan Sindall to deliver the project and initially designed a light thermal upgrade up to RIBA Stage 3. When the Welsh Government introduced their new net zero carbon policy mandating all new building and refurbishment projects to meet NZC targets, the client chose to adopt it, and secured funding from the government’s Sustainable Communities for Learning Programme for additional works.

Whole life carbon analysis

Working to the UKGBC’s NZC guidelines, the design team is taking an informed approach to ensure that Pen Y Dre High School’s operational energy will be zero or negative by enhancing the building fabric and services and offsetting any remaining carbon with on-site renewable energy.

The design and construction team conducted whole life modelling at the start of the project to evaluate the impact of design proposals on both operational carbon (energy used during operation) and embodied carbon (the materials used for building and maintenance) over the lifetime of the building. Comparative options were then developed, tested against buildability, and evaluated in line with capital and lifecycle costs.

The school, which has a steel and concrete frame with masonry infill panels, was in a poor state of repair. Retaining the facade, and introducing insulation, cladding and triple glazing tested the integrity of the structure to its limits, which meant that the team had to work collaboratively to come up with solutions. Five design options were appraised, but only one met the target of net zero based on a whole-life carbon approach over 60 years: full electrification with air source heat pumps (ASHPs) and onsite photovoltaics (PV).

Predicted sustainable outcomes

The enhanced building fabric together with full electrification, will result in zero carbon emissions over the lifetime of the project. Initial modelling indicates that the project’s upfront embodied carbon is 250kg CO₂e/m², well within the government’s 2030 target of 350kg CO₂e/m² .

The retained roof could not take the additional load of PVs, but the school’s grounds are luckily large enough to accommodate the 4500 sqm ground-mounted array. In the summer, when the school doesn’t need that electricity, it can’t be put back into the grid, but discussions are in progress to supply an adjacent hospital.