What does it take to build sustainably? Not so long ago, this question was only asked in the backwaters of the building industry but now it is raised in conferences, board rooms and building sites throughout the UK.
In Brixton, south London, a social housing scheme for Metropolitan Housing Partnership offers a persuasive case for mature, sustainable design: a thoughtful, attractive project fulfils a tough environmental specification with a minimum of fuss and within a realistic budget.
Designed by Anne Thorne Architects Partnership, Angela Carter Close is built on wasteland that once belonged to the gardens of the adjacent Victorian villas. Nine terraced, timber frame houses, with gardens of their own, curve round parking and play areas shared with the council housing next door. The two- to five-bedroom homes are finished in a combination of renderboard and chestnut slats, bringing warmth and charm to this small corner of the dense urban cityscape.
The development looks distinctive amid the stained Victorian brick and post-war concrete of the surrounding housing, but there is little outwardly to indicate the unusual construction and environmental credentials. Yet there is plenty to be proud of, reflected in an EcoHomes rating of Excellent and Forest Stewardship Council (FSC) accreditation under its project labelling scheme, which demands that the bulk of timber and wood products on site are FSC certified. Attention to environmental performance is evident in every aspect of the design.
The houses were based on a timber frame supplied and erected by Devon-based Allwood Timber and made in FSC-certified Ultrajoist, a softwood beam from Glenalmond Timber which is super-dry to give a stable, moisture-resistant product. Allwood also supplied the prefabricated timber wall and floor cassettes, a fast and accurate construction system that generated a minimum of unwanted materials on site. The contractor, Sandwood, has considerable experience of sourcing timber with chain of custody certification, so this was achieved not only for the structural timber, including partition walls and I-joists, but also for window frames, kitchen cabinets and cladding. The chipboard kitchen carcasses, supplied by Symphony, are FSC certified, while the double-glazed Rationel windows are PEFC certified as FSC-certified products weren’t available in the right security spec. The durable sweet chestnut slats came from the Duchy of Cornwall.
The timber frames were made from FSC-certified Ultrajoist
Top-drawer thermal performance required similar attention to detail. Excel Industries’ Warmcel recycled newspaper insulation brings U-values down to 0.18 W/m2K for the walls and 0.13 for the roof. Excel’s Panelvent sheathing boards contribute to these U-values, reduce air infiltration and allow moisture to pass through the walls. The material is made entirely of wood waste and relies on the natural lignin in timber as the material binder. As there are no glue lines, the product cannot delaminate and natural waxes are added to the required sheathing spec. Controlled ventilation in kitchens and bathrooms uses simple passive stack exhaust and trickle vents in the windows can also be opened. A-rated boilers are supported by flat-plate solar collectors for hot water.
Anne Thorne is an enthusiast for the simplicity of the design: “The timber cassettes go up rapidly and the sheathing panels are relatively straightforward to install,” she said. “As well as protecting and racking the walls, they remove the need for tricky layers of plastic or sheathing paper. Assisted by the hygroscopic qualities of the insulation, any water vapour within the walls can move easily through them and out, eliminating the risk of interstitial condensation. The boards also deliver excellent airtightness – 2.3 air changes per hour under pressure. However, the builders were experienced in detailing for airtightness and this experience makes all the difference in delivering this result.”
The project resulted in a diverse range of units on a small site
Water attenuation has also been carefully considered. Sedum blankets on the roofs and porous paving in the gardens and communal areas reduce the flow and speed of rainwater into the drains. Water butts made from old whisky barrels supply the gardens. Inside, toilets have two- and four-litre dual flushes and all taps have flow restrictors.
Other details which help to make this a truly exemplary environmental development include the bicycle sheds, with their own lavender roofs, the use of Auro natural paints, the provision of compost bins and storage space for recycling, the comprehensive use of low energy lighting and the incorporation of habitats for non-human residents: as well as the insect-friendly sedum there are bat boxes on the roofs and a sanctuary for stag beetles in the gardens.
In the hands of a less experienced designer this long list of pro-environmental details could have resulted in awkward homes that failed to work aesthetically, practically or even environmentally. Angela Carter Close is a success because the approach to design was genuinely holistic: thinking through priorities and practicalities from the outset and ensuring that everyone involved in delivering the project understood the design. Happily, a shared professional commitment was easily gained as the team had worked together on a nearby Lambeth Council housing project with a similar environmental specification: Boatemah Walk in the award-winning Angell Town.
The client for the new scheme, Metropolitan Housing Partnership, is pleased with the outcome and impressed with the thoroughness with which the environmental specification was addressed. The project cost more than other contemporary schemes – £1,700/m2 compared with £1,400 elsewhere – but this was mainly because of planning constraints that led to an unusually diverse range of units on a small site.
There is still a premium to be paid for the best environmental performance, not least the effort to gain FSC certification for an entire scheme, but Andrew Cox of Metropolitan recognises the value of pushing the envelope. “The Housing Corporation is demanding ever higher standards from social housing providers. In 2008, all bids will have to meet Code for Sustainable Homes Level 3, which raises the bar higher even than EcoHomes Excellent. It is obviously critical that we can demonstrate our capacity to deliver to this standard.”
There is plenty of debate about the design of sustainable homes. The government’s 2016 zero carbon challenge and longer-term issues about the robustness of our buildings in a changing climate are key concerns. Yet we have come far: Angela Carter Close is one of many contemporary examples of considered environmental design which discreetly demonstrate what can be achieved when all the details are put together with care.
Keywords: Ultrajoist timber frame Anne Thorne Architects
