[STUDY + PLANS + DATA] BPTW Partnership’s Gallon Close is London’s greenest housing terrace, writes Hattie Hartman
A football fan headed to a Charlton match at The Valley stadium would walk right by these houses without batting an eye. No hint suggests that this seven-home terrace is one of the greenest in London. BPTW Partnership’s Gallon Close in the south-east of the city doesn’t flaunt its eco-credentials. Nor is it adolescent green housing, with gawky proportions and ill-fitting renewables.
‘We were well aware of the flamboyance of many 60K schemes,’ says BPTW director Simon Gilling, referring to John Prescott’s ambitious sustainable housing competition of 2005. ‘We wanted to design housing that responded to its context and could be reinterpreted on other sites.’ Early feasibility studies examined options for flats but the London Borough of Greenwich, the site’s owner, has a strong demand for family accommodation, so a brief for four-bedroom terraced housing was agreed.
The scheme’s site plan and massing designed themselves. Welcoming entrances - even the mandatory triple bins for recycling are well integrated - create a pleasant pedestrian environment along Gallon Close, and the carpark fronts on to the inhospitable railway line to the east. The scheme’s most striking architectural feature is its sawtoothed roof form, a response to optimum solar orientation for photovoltaic panels. The result is an unassuming take on the inverted roof that is found on the backs of terraces across London. It looks right at home in the sea of two-storey homes and blocks of 1970s social housing that surround it.
Gallon Close did not set out to be green. Family Mosaic, a repeat client for BPTW, and housebuilder Osborne Homes, who had prior Code for Sustainable Homes (CSH) Level 5 experience in Reigate, were propitious to the mix. The scheme submitted for planning was designed to the mandatory CSH Level 3, with the option to increase to Level 5 should funding permit. As the scheme progressed, it was designed to Level 5, with the possibility of reverting to Level 3 if the funding did not come through.
The scheme’s most striking architectural feature is its sawtoothed roof form
Early contractor involvement during detail design was critical to discuss buildability. Most Level 3 wall construction is either timber-framed inner leaf with a low emissivity cavity, light gauge steel with additional insulation, traditional cavity wall with wider cavities or - increasingly - Standard Insulated Panels (SIPs). The Gallon Close team opted for SIPs because they shaved three months off the programme and are easy to upgrade, by adding a cavity and 60mm of rigid insulation. When the GLA released top-up funding of approximately £30,000 per unit, it was a relatively easy matter to increase insulation and substitute triple-glazed windows and roof-integrated PV tiles. A communal 15,000 litre rain water harvesting system was added.
Despite extensive experience, a lot of the detailing at Gallon Close was new for BPTW. ‘Every sustainability consultant has their own approach, and a lot of these ideas are untested because they fall by the wayside before the end of the project due to costs,’ says Gilling.
There were compromises along the way. The sloped space under the roof, which was intended as full height ceilings for the upper floor bedrooms, was subject to cost-cutting because of the economy of the conventional timber truss. The original designed called for SIPs and a ridge beam. A welcome trade-off for occupants is additional storage, which is at a premium in these homes. Bespoke, louvered, metal balconies, which would have provided additional solar shading, suffered a similar fate, and plastic rainwater pipes on the rear facade replaced the aluminium ones originally specified.
Lightweight timber construction poses a long-term design concern of overheating, and this was aggravated by the east-west orientation of the units. To address this, windows are set into 200mm-deep reveals for partial solar shading.
Biodiversity considerations enhance the car park with native planting and existing. trees are adorned with bird boxes and bug logs. Native species do require more maintenance than the indestructible shrubs conventionally used to landscape social housing - an issue for a social landlord. Ideally residents can be persuaded to look after their own patch or even grow their own.
One of the more remarkable achievements of this scheme was that it was delivered under a design build contract. BPTW opted to visit the site informally every week, and it shows. The air tightness test came in at an impressive 2.5m3/hr/m2. Another achievement is that with the upgrade to Level 5, additional acoustic insulation was incorporated between units, addressing a frequent complaint of social housing tenants. The party walls are double-studded, with triple plasterboard on both sides and an insulated cavity, resulting in a 8db improvement in airborne noise.
The units are equipped with smart meters that show occupants how much energy they are using. However, no post-monitoring is planned. This is an unfortunate oversight - easily corrected - in an otherwise exemplary scheme. If the profession is serious about delivering low-carbon buildings, we have to know how they perform. It’s too easy to rush onto the next project after all the hard work.
While BPTW is rightly proud to have delivered newbuild housing that is affordable, contextual and sustainable at Gallon Close, its next project just might be housing refurb. ‘Now it’s all about retrofit,’ says Gilling. ‘Refurb may not be glamorous but it’s a challenge architects need to address.’ And there are 26 million homes waiting.
Start on site January 2009
Contract duration 42 weeks
Gross internal floor area 888m²
Form of contract Design and build
Total cost £1.5 million
Cost per m² £1699.10
Client Family Mosaic
Architect BPTW Partnership
Structural engineer ONE Engineer
M&E consultant ISO Energy & CSA
Main contractor Osborne
SIPs Innovare Systems
Insulation Celotex and Greenloft
Photovoltaics Solar Century
Rainwater harvesting tank Polypipe
Annual CO2 emissions -0.7kg CO2 /m2
Gallon Close, Charlton by BPTW Partnership