Prefabricated panels erected on site in three days
Hidden in the bend of Aden Grove in Hackney, Elsie Owusu Architects’ low energy house is a modest two-storey dwelling. Originally a parking space for the adjacent end terrace, the site has been transformed from a disused overgrowth of vegetation to a compact 70m2 home for private clients. Its white render façade and clean orthogonal form makes for an unashamedly modern contrast with its neighbours.
The project was a long time coming to fruition, with a gap of seven years between inception and completion. Architect Elsie Owusu, who is also a partner at Feilden + Mawson, explains that the delay was due to opposition from the neighbours – 30 objections were received to its first planning application.
The revised scheme lost its photovoltaics as well as the basement level which, aside from being potentially too disruptive, was halted by discovery of a mains pipeline on the site.
The loss of the basement makes the house incredibly compact, although sliding doors and a spiral staircase make the most of the tight plan.
From the street, the most notable feature of the house is a large glass facsimile of a collage entitled ‘Memories of Place’ by Sir Peter Blake, whom Owusu previously collaborated with on Feilden + Mawson’s UK Supreme Court renovation. Blake’s collage at Aden Grove is made up of objects found during the digging of trial pits at the site: an oyster shell, facing of a brick wall, blue-and-white Victorian china and a fragment of clay pipe.
Blake’s involvement with the project began in 2005 and was supported by a small Arts Council grant. Speaking to Footprint, he commented on his enjoyment of the process and professed his lifelong interest in architecture: his first work was actually bought by Colin St John Wilson who designed extensions to Blake’s own home.
Despite the obvious celebration of his involvement with the project, both Blake and Owusu concur that it could have been greater still. Conceptually Owusu cites Blake’s ideas of self-sufficiency, as embodied in his ‘Brotherhood of Ruralists’ in the 1970s, as inspiration for the house’s approach to low energy use.
The project was developed with the ‘low energy design team’ at contractors’ Richardson and Peat, who had previous experience with the Passivhaus standard in the education sector. The house was designed according to the Passivhaus principles, but the design team opted against certification. Sustainability engineer Phil Neve of Aaben notes, ‘There were a number of factors that worked against achieving Passivhaus certification.’ These included the taller terrace to the south limiting solar gain and the constrained site footprint restricting wall thickness.
Reaching the appropriate U-values was a delicate balance between retaining floor area and increasing insulation in the walls and floor, the latter being especially pertinent due to the scheme’s polished concrete floor.
In the end, the project achieved reasonable U-values by using high performance insulation and designing out thermal bridging with a relatively slender 300mm wall construction.
As for air permeability, despite there being no space to incorporate MVHR, the house still managed to achieve a measure of 2.6 on the air-test. Service voids built into the interior surfaces helped prevent the airtightness being compromised by the fitting of services during construction and also allows for flexibility in future.
Full height triple-glazed windows are almost entirely single aspect towards the northeast, allowing for natural cross-ventilation across the open plan ground floor. This and the top light which pokes through the green roof over the landing mean the house is full of natural light.
The most remarkable aspect of this project was its speedy construction. Prefabricated cassettes of structurally insulated panels (SIPs), glulam and timber beams were produced in six weeks and assembled in a factory in Bedford so that the client and architect could actually walk through and experience a 1:1 model of the house.
The frame was then disassembled, transported to site, craned into place and water-tight in 72 hours – despite one of the roof steels being 60mm too long, due to bowing of the party-wall. The panel system, devised by the contractors with consulting engineers Conisbee in school designs, helped with managing the difficult site access and greatly reduced waste.
Considering the restricted nature of the site and lack of renewable technologies, the carbon reductions as listed below make for an impressive result.
Owusu now plans to use her experience on the house to develop a prototype for low-energy housing in her native Ghana, noting: ‘I think off-site (fabrication) combined with Passivhaus is an interesting model, especially in developing economies.’ She envisages the prototype could eventually lend itself to a self-build business and design model.
SAP Assessment - annual predictions
Space heat demand: 2300 kWh
Space heat costs: £80
Hot water demand: 2100 kWh
Hot water costs: £70
Annual C02 emissions: 17kg/m2 [5% improvement of Dwelling Emission Rate (DER) over Target Emission Rate (TER)]
U-values - W/(m²K)
Architect: Elsie Owusu for Elsie Owusu Architects
Collaborating artist: Sir Peter Blake
Contractor: Richardson & Peat
Consulting engineer: Conisbee
Sustainability engineer: Aaben
Supporting architects: Mark Ellerby Architects
Glass art consultant: Andrew Moor
Completed May 2012
Elsie Owusu collaborates with Sir Peter Blake on low energy house in Hackney