Passivhaus library in Grade I Oxford College setting

The Spencer Building for Corpus Christi College in Oxford combines newbuild Passivhaus construction and heritage conservation. The recently Passivhaus certified project includes a library extension and special collections archive, safeguarding a world-class collection while minimising the building's operational energy use. It is the UK's first Passivhaus certified library.

The Spencer Building is an ambitious new build project designed within a constrained conservation site, requiring historic façade retention on three sides. Designing to rigorous Passivhaus standards in a historic site posed challenges, particularly in achieving high levels of insulation and airtightness within the retained historic fabric. PHT Patron Max Fordham was Passivhaus Consultant on the project, with PHT Patron WARM as Passivhaus Certifer.

The design aimed to simplify the form as far as possible to minimise surface area heat loss and simplify insulation details. Two different zones were developed within the building - the archival stores and the occupied library spaces - which are thermally separated to avoid heat gains, and dealt with separately for Passivhaus Certification. The archive was placed in a new insulated, airtight concrete bunker built against the City Wall, harnessing its thermal mass to create stable, low-energy environmental conditions for the collections. The library section was optimised to make the most of the available natural light from the building's east side, resulting in generous, evenly lit library spaces with dramatic views upward to the sky, and a reduction in the need for artificial lighting.

The Spencer Building, Corpus Christi College, University of Oxford. Image credit: Wright & Wright Architect

Key stats

Construction: Reinforced concrete frame & steel frame
TFA: 469 m² main building, 90m² archive
Build start date: 2021
Completion: 2024
Certification: Passivhaus certified, 2025

Spencer Building, Corpus Christi College, Oxford. Image credit: Wright & Wright and Hufton + Crow

At Corpus, we are always mindful of our responsibilities as custodians of our College’s history and also its future. In that light, we are delighted at the news that the Spencer Building has secured full Passivhaus accreditation. This achievement truly embodies our vision of encompassing simultaneously the best of the old and the best of the new.

Professor Helen Moore, President, Corpus Christi College, Oxford

Spencer Building, Corpus Christi College, Oxford. Image credit: Wright & Wright and Hufton + Crow

Construction

The new building was built within a highly constrained site, framed by three historic features: the medieval City Wall to the west, a listed façade facing the Garden Quad to the east, and the College’s Old Library to the south. Historic fabric is retained on three elevations. A new limestone facade was used for the other elevation. Incorporating high levels of insulation has increased the depth of the walls and roof on an already tight site. In addition, the airtightness boundary was carefully considered to ensure the hygroscopic historic stone walls avoided unwanted build up of moisture.

The Spencer Building, Corpus Christi College, Oxford. Image credit: Nick Hufton, Wright & Wright

Maintaining the existing medieval stonework on some elevations significantly reduced embodied carbon, but resulted in some complex detailing to meet Passivhaus requirements. To minimise thermal bridging within the retained façade, rigid structural thermal break pads were used to connect the new steel frame to the existing retained structure. On the west elevation, stainless steel wall ties were used to connect the new stone cladding areas back to supporting structure.

U-values

Floor: 0.10 W/m²K

Concrete floating slab over PIR/ XPS insulation, mineral wool in basement.

Spencer Building, Corpus Christi College, Oxford. Image credit: Wright & Wright and Hufton + Crow

Wall: 0.15 W/m²K

Timber frame, concrete ground floor (due to flood resilience planning requirement)

Roof: 0.11 W/m²K

Mineral wool insulation, mix of steel frame and timber

Building performance

Spencer Building, Corpus Christi College, Oxford. Image credit: Wright & Wright and Hufton + Crow

Designed energy performance

Airtightness

0.56 @ 50 Pa for main building

0.5 @ 50 Pa for archive

Space Heating Demand (≤ 15 kWh/m².a)

15 kWh/m².a for main building

Heating Load (≤ 10 W/m²)

11 W/m²

Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)

65 kWh/m².a area-weighted average. Bespoke PER limit.

Primary Energy Renewable Generation

13 kWh/m².a (against building footprint).

*This exceeds the Passivhaus limit, due to the non-standard usage pattern of the building. A bespoke PER was submitted to the Passivhaus Certifier. +/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Over the years, we’ve found that following the Passivhaus process, and fully committing to achieving certification, results in buildings that use very little energy, that also stand the test of time. The lessons learned from this project are already spreading, informing new developments in Oxford and beyond. The project shows Passivhaus can successfully be delivered in a constrained site, with a range of space uses, within a heritage setting, and while delivering stunning architecture.

Gwilym Still, Passivhaus Director, Max Fordham

Services

Heating strategy: Space heating is delivered via low-temperature systems fed by a ground-source heat pump (GSHP). The boreholes for the GSHP also provide low-energy cooling to the archive space. The building uses an all-electric services strategy to meet conservation requirements, long-term energy performance, and environmental impact. Domestic hot water is delivered by local point-of-use appliances. The hot water demand is relatively small, and the project team wanted to avoid significant distribution losses through the building.

Ventilation strategy: A central MVHR system with heat recovery provides continuous fresh air to reading spaces while maintaining stable temperature and humidity for the collections. Ventilation of the archive is delivered via a primarily recirculating unit, with relatively low outside air flow rates, and timing of outside air supply to make use of free cooling when available.

Summer comfort strategy: Summer comfort is managed through external shading, carefully sized glazing, the thermal mass of the concrete archive bunker, openable windows, and controlled night-time purging via the MVHR system, and summer bypass of the heat exchanger, to limit overheating without the need for conventional air-conditioning.

Renewables: A modest array of solar PV panels on the roof contributes to the building's electricity supply.

Challenges & lessons learned

Spencer Building, Corpus Christi College, Oxford. Image credit: Wright & Wright and Hufton + Crow

Retention of heritage façade: The building sits between the medieval City Wall, the College’s Grade I listed Old Library and retained elements of the former President’s Lodgings. Responding to this in the designs was an atypical challenge to overcome when aiming for Passivhaus certification. Archaeology, party wall conditions and the highly constrained site influenced the programme, materials chosen and sequencing of the works. Early coordination with the client, heritage bodies, engineers, contractor and Passivhaus Certifier was necessary to manage these constraints. Incorporating significant surrounding historic fabric into the envelope of the building required detailed and intensive surveying, design work and updating of details throughout the build to ensure coordination of airtightness, insulation, structure and services to deliver a certifiable scheme. Rather than looking at the historic fabric purely as a constraint, it was instead looked at as a starting point that could enrich the architectural design. The structural layout and servicing zones were arranged to allow future changes in use, access requirements and building services without major intervention to the historic fabric.

Separation of library & archive: Creation of a thermally separate archive bunker against the historic City Wall was an early design consideration. The construction and environmental strategy needed to be established from the outset for this to be deliverable on site.
Glazing ratio: Providing 55 naturally lit, functional readers spaces was a crucial client requirement. Balancing the glazing ratios of windows and roof lights to meet daylighting and overheating requirements was a key focus throughout the design process.
Airtightness challenges: Airtightness testing of the main building was challenging due to interfaces with existing buildings to both north and south. Workshops with the design team, contractor, and airtightness tester were useful in agreeing a workable process. If designing the project again, the team might consider some ‘sacrificial’ airtightness line between to all interfaces between new build elements and existing retained fabric. On the south elevation of the building, the strategy effectively made the building airtight against the neighbouring existing. This typically is not required but made the airtightness testing of the new thermal envelope sleeved behind much more straightforward. At the north, not all of the interface between new and existing fabric was made airtight. This made airtightness testing more challenging. If doing the project again, all new to old interfaces would be treated similarly to help with the clarity of the testing strategy and quality control, rather than because it would be necessary for the operation of the building.
Product specification: For some elements of the thermal envelope,the project team found it difficult to find a product that met all the requirements. This was particularly the case for the archive doors, which needed to be secure, be thermally efficient, airtight and have a significant fire rating.
Communication: Benchmarking key details was important, to communicate and agree the required quality standard before significant works were carried out. These benchmarks also assisted with statutory planning condition approvals. Communicating key commissioning requirements helped the MEP commissioning process run smoothly.

Architect’s view

Existing elements and conditions were a starting point, not a constraint. The Spencer Building emerges from Corpus’s historic fabric, generating unexpected synergies and introducing sustainable, inclusive and forward-looking spaces.

Clare Wright, Founding Partner, Wright & Wright Architects