COMMENT SITE LINES
How ‘zero compromise’ do architects need to be when designing envelopes to the Passivhaus standard and are aesthetic, and other compromises necessary? Sarah Johnson reports on the challenges involved
Going for the ‘gold standard’ T
he Passivhaus standard is often seen as the ‘gold standard’ for building performance. Passivhaus buildings provide a high level of occupant comfort while using very little energy for heating and cooling. They are built with meticulous attention to detail and rigorous design and construction per prin- ciples developed by the Passivhaus Institute in Germany. The fabric, or envelope, of a Passivhaus, needs to achieve high thermal and airtight performance while providing structural stabil- ity and weather protection. For building durability, the building also needs to eliminate the danger of interstitial condensation forming within the structure.1
The key principles of Passivhaus
design include: •continuity of super insulation; •minimising thermal bridging; •maintaining airtightness; •minimising thermal bypass.
A rigorous approach is needed when it comes to designing build- ing envelopes which will provide the necessary performance for a project to achieve Passivhaus accreditation. Passivhaus buildings can be built out of any construction material and therefore a wide variety of building envelope details are required to deal with the challenges of limiting thermal bridging and creating an airtight layout to meet Passivhaus criteria.
Passivhaus criteria do not dictate what construction methods should be used, but the following case studies of certified Passivhaus projects illustrate a range of scales, materials and typologies. In each example, the architects were asked three key questions about their project.
CASE STUDY: THE UNIVERSITY OF LEICESTER
The University of Leicester’s Centre for Medicine building is currently the largest commercial Passivhaus in the UK. It consists of a concrete frame and curtain walling.
Architect’s View: Jonathan Chadwick – Associated Architects
Why were the materials and the construction method adopted? Brick was chosen as the predominant material for the facade as it respected the character of the neighbouring building and the site’s location on the edge of a conservation area. The use of curtain walling modules to panelise the brick facade provides a contempo- rary architectural language whilst remaining sympathetic to the surrounding context.
Curtain walling lent itself to the rigours of achieving Passivhaus
levels of facade performance as it reduced the number of interfaces between different subcontractors’ work packages and provided a high degree of certainty that levels of workmanship would remain consis- tent. The use of ‘tried and tested’ building components also gave the client confidence that long-term appearance and performance would be maintained without significant additional ongoing costs.
What was the main challenge in meeting Passivhaus? Refining the details of the curtain walling to minimise thermal bridging and to integrate the controls for the external shading blinds was complex and hadn’t been done to Passivhaus levels of performance in the UK before.
Extensive design development was carried out by the contractor’s design team in conjunction with the facade sub-contractor, Passivhaus specialist, curtain walling manufacturer and facade engineer to ensure the design was robust and repeatable whilst maintaining the required aesthetic.
A large mock-up panel was produced off site at a testing facil- ity to enable the technical resolution of the details to be refined and weather tested to CWCT standards prior to inspection by the client.
How ‘zero compromise’ was the design and were any aesthetic compromises made?
The Passivhaus standard of performance is very exacting and numerous detail design refinements were reviewed and thermally modelled prior to the curtain walling going into manufacture. This extended detailed design period is necessary with Passivhaus proj- ects to ensure that aesthetics are not compromised in the pursuit of technical performance where new technologies are being pursued.
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ADF FEBRUARY 2017
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The University of Leicester © Martine Hamilton-Knight
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