Report – Massive Passiv: Applying Passivhaus to Larger Scale Developments

Date posted: June 2, 2017

We recently hosted our Green Sky Thinking event ‘Massive Passiv: Applying Passivhaus to larger scale developments’.

Using new build student accommodation as an example, a panel of speakers explored how Passivhaus can raise the bar in terms of building design and construction quality, as well as the benefits to owners and users over the building’s lifespan.

Sally Godber of Warm gave a brief introduction to the principles of Passivhaus, what it means in terms in both design and cost terms to the end user. She busted some myths, such as the common misconception that you can’t open windows in Passivhaus’ – “not true!”; that ventilation systems are noisy and expensive – again, this is not the case; and that it is all about houses – Passivhaus is suitable for anything that has a heating demand or a need for atmospheric comfort. Offices, schools, flats, care homes – these are all excellent fits for Passivhaus.

Sally cited numerous reasons why we should pursue the standard, as it can have positive effects on the health and happiness of occupants; it has low maintenance costs; brings low rent arrears and turnover of tenants; and through high levels of workmanship and its rigorous quality assurance processes it ensures a long-lasting building fabric. Primarily, it is about providing comfort for the end users.

In technical terms, the two key challenges in her view are the building form and glazing. If your building steps in and out in section as well as plan, then achieving Passivhaus gets complicated. Glazing, which is triple glazed as standard in Passivhaus, needs to ‘make its money’ by, for example, achieving the right balance between the amounts of shading and daylight, while ensuring that any potential overheating problems are designed out.

A lifecycle and capital cost perspective was provided by Paul Cavanagh of Gleeds, whose experience includes Passivhaus and student accommodation schemes. He shared benchmark figures putting the cost of Passivhaus at between 11-22% (average 14%) higher than a traditional solution. This was caveated with the note that five years ago these figures were 4-5% higher, and are decreasing as the market adapts to Passivhaus requirements.

Paul identified two critical factors for Passivhaus: one, which makes the cost of applying it higher, is that the higher construction quality comes at a cost; and a second vindicating factor is that the costs of energy over the long term have risen and seemingly will continue to do so, which will deliver increasing savings for the user.

Paul shared a 60-year profile for a 10,000sqm student accommodation building, which projected payback at year 13, and which over the 60-year period would deliver a saving of £6.3m –  including a 51% saving on energy.

ArchitecturePLB Associate Paul Phasey, who is the practice’s accredited Passivhaus Designer, spoke about the challenges and benefits of scaling Passivhaus up, referencing the practices experience on West Hill Green and Stapleton House student accommodation schemes. In applying Passivhaus to these projects, the key principles of the standard still apply, but building at scale has a number of implications: Insulation – treating the building as a whole, regardless of number of units within, leading to gains envelope efficiency; Windows – savings can be made on glazing through economies of scale, but as designers we need to beware the dangers of overheating; Ventilation – many student accommodation schemes already have a Mechanical Ventilation with Heat Recovery (MVHR) system so only slight enhancements would be needed here, but at scale there will always be a need for M&E; Airtightness – get the details right and roll out at scale; and Thermal Bridging – a key aspect and the most difficult to address due to the nature of construction at height and scale.

Paul’s analysis revealed that the form of the student accommodation blocks studied would require minimal enhancements over a building regulations standard to achieve Passivhaus.

He also acknowledged the importance of the ensuring that every building integrates well in to its urban context – Solar Design vs Urban Design –  and how the architecture and urban design needs to be balanced with the schemes approach to Passivhaus and its sustainability credentials.

Following the talks, an enthusiastic audience of estates directors, developers and consultants debated the topic, with further discussion of both the opportunities and challenges of upscaling, overheating, comparative costs and construction skills training required to achieve Passivhaus at scale.

A common consensus amongst all speakers was the need for Passivhaus to be integral to the project from the outset (as opposed to be being added on at RIBA Stage 3 or 4), and for modelling to be used throughout the process to ensure components are optimised and savings maximised. The overall conclusion was that achieving Passivhaus on larger scale schemes would not result in considerable changes to the fabric of a ‘typical’ scheme, due to the benefits gained from building at scale.

If you would like to discuss further any of the points raised in our event or to find out more, please get in touch via marketing@architectureplb.com