Two Rivers Primary School

We provided Passivhaus input from feasibility stage through detailed design and construction. This included:

• Airtightness: We advised on the design of the building to make it easier to achieve the required level of airtightness and supported the design and construction teams in delivering this. Two Rivers Primary School achieved 0.4 air changes per hour (ACH), significantly better than the Passivhaus limit of 0.6.

• Simple form and good orientation: These played a major part in achieving success on the project, as it helped limit the fabric performance requirements, and allowed the school to be constructed within budget.

• Steel frame: This is the primary structure, which is unusual for a Passivhaus building. We were involved with the evaluation and design from the initial feasibility study through to practical completion and beyond to help make the design work with the strict Passivhaus Plus requirements, including helping to control thermal bridging and buildability.

• Ventilation: Low energy use ventilation that delivers high air quality is a key element of Passivhaus, and plays a very significant role on Passivhaus schools. We supported the team in developing an efficient cascade ventilation design, which limits energy use and ensures students receive a supply of fresh air throughout the day. Summer comfort is achieved via both the mechanical ventilation system and opening windows.

Initial performance data shows an energy use intensity of 45 kWh/m²/yr, below the LETI Climate Emergency Design guide (65 kWh/m²/yr), RIBA 2030 Challenge (60 kWh/m²/yr for 2030), and DFE School Output Specification (52 kWh/m²/yr). This is total energy used, whether from renewables or the grid. 

The PV system generates energy equal to 93% of the building's annual consumption, with 2/3 of this used in the building, and the remainder exported to the grid. 

The school has given outstanding feedback on the internal environment, being particularly pleased with the thermal comfort enjoyed throughout the year. Contractor ISG praised the benefit of the Passivhaus standard leading them towards a greater degree of cost certainty earlier on in the project than they would usually have. With all parties working toward a shared goal with set, measurable targets, the team formed a highly collaborative working environment. This effort was recognised with an award for ‘Integration and Collaborative Working’ by the Construction Excellence Awards 2023.