Building for change
The Passivhaus Standard explained
This year, many estates offices are taking stock as universities head towards the end of their first carbon management plan (CMP) periods.
In addition to the challenges posed by the growth in campus size and student numbers, several have been faced with a performance gap between the predicted energy demand and carbon emissions from new or renovated buildings and their actual performance.
As the country now looks towards even more ambitious net zero carbon targets, finding building approaches which can close this gap is becoming increasingly vital. One proven option is constructing to the Passivhaus Standard.
Passivhaus sets clear energy performance targets designed to allow the creation of buildings which require little energy to heat or cool, while providing a high level of comfort for occupants.
Performance targets for a European climate
Primary energy demand
≤ 120 kWh/m2/yr
Space heating/cooling demand
≤ 15 kWh/m2/yr
Specific cooling load
≤ 10 W/m2
While these do not specifically address a building’s carbon emissions, in practice they should significantly limit emissions when compared with a property built to current Building Regulations/Standards. The Standard is backed by a rigorous certification process, and post-occupancy monitoring suggests that, on average, actual energy performance of these properties meets or outperforms the design prediction1.
The external fabric of a Passivhaus property typically needs to be insulated to meet a U-value of 0.15 W/m2K, or lower, and be fundamentally ‘thermal bridge free’. Close attention to detailing is crucial to ensure that potential thermal bridges around openings and at junctions are properly addressed. In addition, air-leakage rates must be no higher than 0.6 ach@50 Pa. This is typically achieved by installing an airtight layer, such as oriented strand board (OSB), and airtight tape, which is applied to seal all junctions.
While it is possible to meet these envelope requirements with traditional construction methods, offsite construction approaches such as Structural Insulated Panels (SIPs) can provide a simpler, faster and more adaptable solution.
SIPs feature an insulated core sandwiched between two layers of OSB, with a jointing system that ensures excellent insulation continuity throughout the envelope and limits air loss. They are designed and pre-cut to each project’s precise plans offsite, allowing rapid and accurate construction.
By assessing all junctions and openings within the building envelope and carefully installing additional insulation, thermal bridges can be eliminated and the U-values and air-leakage rates reduced to the required levels.
The airtight designs necessitate good ventilation typically via a mechanical ventilation with heat recovery (MVHR) system. MVHR systems extract the heat from outgoing stale air and transfer it to warm incoming fresh air, further reducing heating demand and ensuring a fresh, comfortable environment within the home.
The Passivhaus Standard has been successfully met on several UK university buildings, including an accommodation block at Leeds Beckett University’s Carnegie Village campus which became the first Passivhaus certified student accommodation in 2010.
More recently, the University of Nottingham integrated Passivhaus measures within its Research Acceleration and Demonstration (RAD) Building, a 2000m2 facility incorporating advanced laboratories. SIPs are utilised within the outer façade to provide excellent fabric performance and airtightness and the building is designed to achieve a rating of ‘Excellent’ under the BREEAM sustainability standard.
As the climate emergency deepens, research suggests that a growing number of students would factor an institution’s commitment to the environment into their choice of university2. By adopting building approaches such as Passivhaus, universities can have greater confidence that buildings will perform to their expected level, forming a more reliable part of their overall CMP.
1 Rachel Mitchell, The Performance of Passivhaus in New Construction (Passivhaus Trust, July 2017)
2 2019 College Hopes and Worries Survey Report (Princeton Review: https://www.princetonreview.com/cms-content/2019-College-Hopes-Worries-Survey-Report.pdf)