Black Barn reaps Passivhaus benefits
A striking black barn in the flat fen landscape near Peterborough is the manifestation of its architect’s commitment to Passivhaus: the building houses the offices of PHT member Swann Edwards Architecture, providing prospective clients with the perfect model of persuasion of the high levels of occupant comfort with minimal energy use inherent to Passivhaus certified schemes. For those who are not able to visit, a virtual tour gives a flavour of the experience.
On arrival, visitors to the office immediately gain an insight into the inner workings of a Passivhaus building when they see the Paul Novus MVHR unit in pride of place in the reception area, and exposed rigid steel ductwork supplying constant fresh air to the working environment at a comfortable temperature.
Orientation and form
The architects' previous experience in passive solar design and earth-sheltered buildings gave them a foundational understanding of the importance of orientation and form in achieving a high-performing building without having to rely on extra measures such as more insulation to compensate for energy loss. The basic form of the building is simple, architecturally referencing the traditional rectangular pitched roof shape of an agricultural building, and at the same time benefiting from a good heat loss form factor.
The mass is then pushed and pulled to create openings, recesses and overhangs, managing shade and light to great effect. The inset gable end creates a simple and bold visual statement while functionally sheltering a first floor balcony. Such measures significantly reduce the risk of overheating, and with the further aid of strategically placed north and south openings and deep reveals throughout, a comfortable internal temperature of 25° is maintained even when it soars to 35° outside.
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We are now reaping the benefits of adopting this approach both in terms of occupant comfort (particularly evident during the hot summers - 35° externally and 25° internally), running costs, demonstrations with visits by clients, general public and professional bodies, and business growth with several of our clients adopting the Passivhaus approach.
James Burton, Director, Swann Edwards Architecture Ltd
Internally, true to its agricultural inspiration, the aesthetic is sparse and honest to its materials. The blockwork walls are left exposed, the concrete floor is polished to a high shine, and the plywood ceiling stays naked. Outside, timber i-joists fixed to the blockwork create a void for 350mm Warmcell insulation, enclosed with Isolair insulation board, and finished with charred larch cladding to complete the look. The same depth of Warmcell insulation between i-joists continues over the roof, keeping the building snug, with u-values of 0.116 for the roof and 0.127 for the walls achieved.
Progression doors and windows from PHT member 21 Degrees - who also designed, supplied and commissioned the MVHR system - complement the barn aesthetic with their minimal sightlines while at the same time offering excellent whole window u-values and installation psi values.
Passivhaus performance
Airtightness is achieved with Intello membrane at ceiling level and a layer of render within the build-up of the blockwork walls. After an initial attempt to rely on 18mm OSB to provide airtightness proved unsatisfactory (not all OSB is airtight), membranes were added to resolve the issue, with retrofit contractors Nesthaus enlisted to bring their experience to the task of successfully sealing the building. The final airtightness test came in at 0.4ACH, comfortably within the 0.6 Passivhaus target.
The office makes efficient use of space as well as resources with 14 occupants in 262m² GEA, providing flexible accommodation and minimal maintenance and operational costs. Existing equipment was reused, and together these factors persuaded the certifiers, PHT member WARM, to allow a primary energy demand over the usual Passivhaus target.
Key Facts |
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Energy performance
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Start date on-site: October 2015 Certified: January 2018 TFA: 175.3m² Cost: £495,000 |
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Thermal energy demand (≤15): 11 kWh/m².yr Primary energy demand (≤135): 162 kWh/m².yr Airtightness (≤0.6): 0.4 ACH |
The total project costs of approximately £1890/m² are testament to the efficiency of the design and cost-effective approach taken by Swann Edwards. This cost includes preliminaries, insurances, service connections, external works, fencing, signage, kitchen but excludes consultants, application costs and furniture costs. The costs could have been kept down further but for some conscious decisions to select materials of a higher quality and cost in order to achieve the desired outcome. The distinctive feature cladding, for example, cost around £61k to supply and install; an alternative solution might have been achieved with around a £30-40k saving.
From the outset, our intention was to be sympathetic to the agricultural history of the area and to create a contemporary interpretation of a barn development, with the ethos of environmentally responsible development and sustainability at its core."
Jamie Burton, Swann Edwards Architecture
Key Team |
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Client: Swann Edwards Architects: Swann Edwards Architecture Contractors: NB Construction (UK) Ltd, KB Construction Ltd, Mark Johnson, Cambridge Flat Roofing, Nesthaus Structural Engineers: Geoff Holyoake Associates Ltd Consultants: 21 Degrees, Alan Clarke, Bloom and Wake, Foster Renewable Energies Ltd Certifier: WARM |
The architects set themselves an additional challenge by also acting as Principal Contractor, but gained valuable experience and understanding for delivering future Passivhaus schemes over the course of the build. This stood them in good stead for their work on Far Few Barn, a paragraph 55 home recently featured on Channel 4's Building the Dream. Join us at Futurebuild at London's ExCel in March to learn more about it – as one of three featured projects in the Passivhaus Superstars session, it will be presented by architect James Burton.
All images courtesy Swann Edwards Architecture
Further information
7th January 2020
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