SPECIAL FEATURE MAYVILLE


he science of climate change is presenting the global built environment with some stark choices. Carry on as we are, and buildings will contribute hugely to the rise in greenhouse gas emissions. Focus on zero carbon new build, and we’ll only improve 1-2 per cent of the buildings every year.


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The bare fact is that carbon reduction targets of 60 per cent or more cannot be achieved without a deep retrofit programme of existing buildings. Nearly 90 per cent of those buildings will still be operational in 2050, so tinkering around the edges with new build won’t be enough.


A more radical approach to refurbishment is needed, where energy use is driven down so that remaining demands can be easily covered by renewable or low carbon fuel sources. The first step is to reduce heating loads by high levels of thermal insulation and fabric airtightness. The second step is to increase the efficiencies of the heating, cooling and lighting systems, and to ventilate naturally or by mechanical ventilation with heat recovery where appropriate. The third step is to use low carbon sources of fuel.


This, in essence, is what drives the


Passivhaus approach. Widely practiced in Europe, Passivhus is now making inroads in the UK. The key question is whether what works in mainland Europe is appropriate for the wetter, milder UK, with often densely occupied spaces and longer hours of operation.


The Mayville Community Centre project in Islington, North London, is a case in point. The project involves the complete refurbishment of an existing 19th Century brick building into the first non-domestic, fully certified Passivhaus refurbishment in the UK.


PROCUREMENT Built in the 1890s as a generating


station for London’s tram network, the massively constructed building was rescued from dereliction in 1973 by the Mildmay Community Partnership and turned into a community centre for the local Mayville Estate.


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COMMUNITY CENTRE – Passivhaus project case study


In 2006 bere:architects was asked to refurbish and extend the rundown building. Initial thoughts had been to heat the existing building with a biomass boiler, but Justin Bere quickly calculated that they would need “juggernauts of wood” to cope with a leaky (asbestos) roof, leaky windows, and hardly any insulation. Rather than simply extend the


building, Bere reasoned that more space could be generated through efficient internal replanning and by adoption of Passivhaus principles. The community trust agreed. Procured under the JCT SBC/Q 05, refurbishment works to the building include internal space replanning to create an extra 35 per cent usable space for both local community use and renting to small fledgling businesses.


The building’s accessibility was improved and a full upgrade of the fabric and its environmental systems was planned to meet the Passivhaus standard. The construction budget was £1.6 million.


SITE ASPECTS


The existing building, orientated due north south, is a three-storey concrete- framed building (basement, ground and first) with a nominal 600 mm-thick solid brick skin, pitched roof and a later single- storey extension. Although the building is situated within community gardens, they were not easily accessible. The rebuild aimed to improve this. An enlarged single-storey entrance block with reception and dining area was added, along with access to the south garden. Enlarged openings to the ground floor south elevation also allows access to a south garden (increasing winter solar gain). A south elevation lightwell, down to basement level, allows in natural light, ventilation, and solar gains, and provides access to the basement.


The additions have increased the usable area by about 35 per cent. The treated floor area is 665 m2


. Work started


on site May 2010 and was completed in July 2011.


BUILDING FABRIC


Bere Architects took an incremental approach to improving the building.


PUBLIC SECTOR SUSTAINABILITY • VOLUME 2 ISSUE 1


Primarily this involved improving the efficiency of the fabric and a new roof. As part of the refurbishment works, the external walls were damp-proofed down to the footings. Originally the slab had a damp-proof membrane, with the bitumin carried up the outside of the building. Unfortunately a 20 m drainage trench had to be cut though that membrane. Despite being made good, the replacement membrane remains a slight concern to the design team. The Passivhaus Institute recommends insulating underneath new buildings, but here that wasn’t practical. An alternative is to create what’s termed a thermal bubble underneath the building, whereby insulation below the ground is taken out horizontally for a certain distance. At Mayville it was decided instead to carry the external insulation right down to the foundations and add 75 mm of high performance phenolic insulation on the building’s basement concrete raft. The walls above ground level were treated with 300 mm of expanded polystyrene block fixed to the external face of the brickwork and finished with a protective hardwearing Permarock render. Below ground the basement walls are externally insulated with 200 mm of extruded polystyrene insulation. A replacement zinc pitched roof with 400 mm of insulation was installed over the top of the existing steel trusses. A layer of 300 mm Rockwool insulation was placed between the joists, with 100 mm of denser Rockwool over the top of the steel structure to avoid cold bridges. The top of the insulation is covered with a Tyvek breathable membrane and finished off with a standing seam zinc roof. All windows were replaced with high


quality, German triple-glazed windows with detailing that avoids thermal bridging. Careful attention was paid to both the detailing and the quality of insulation.


The window frames are positioned with inflatable bags, and fixed with screws that locate but do not put any pressure on the frame itself. The window frames were sealed into the openings with continuous tape. To ensure that contractors could follow instructions, the architect generated


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