The Elmswell 'Three Gardens' Affordable Housing project

Delivering low carbon emissions at the ‘Three Gardens’ affordable housing project

The scheme was commissioned following a design competition organised by Orwell Housing Association and the Suffolk Preservation Society, in response to the lack of housing affordable for locals in a rapidly-growing commuter belt. The overall design, by London architectural firm Riches Hawley Mikhail Architects, won a 2007 Housing Design Award last October and was commended by the Award’s panel for its ‘sense of benign local ecology throughout’.

Sustainability was always central to the concept. “The scheme will have very low in-use and embodied carbon emissions compared to almost any other multi-unit residential project completed in the UK to date,” said Alasdair Young, sustainability engineer and project leader from Buro Happold’s SAT (Sustainable and Alternative Technologies) team in London, which was responsible for the sustainability aspects of the design.

Aiming for Eco-Homes excellence and low in-use emissions

The project features a number of systems which yield low in-use carbon emissions. The biomass community heating network is fully automated, and each dwelling individually controlled, whilst emitting significantly less CO2 than localised gas boilers. Equally, the use of woodchip from the area’s trove for heating and hot water is a carbon neutral solution, relying as it does on renewable local fuel.

Meanwhile, energy efficiency at Three Gardens is primarily achieved through the use of whole-house ventilation with heat recovery, improved air-tightness and highly insulated walls. These measures, together with the biomass boiler-fired community heating system, will help the development reduce carbon emissions by around 60%, compared to a standard regulations-compliant building.

“Three Gardens aims to achieve an Eco-Homes ‘excellent’ rating as well as being a first-rate example of cost-effective, sustainable design,” said Young.

‘Hemcrete’ locks carbon into the structure, minimising embodied carbon

Increasing the development’s environmental credentials, the houses are timber-frame constructions, and the walls will be made from ‘hemcrete’ sprayed onto the wooden formwork. ‘Hemcrete’ is a hemp-and-lime matrix which has excellent environmental and thermal properties. One of the region’s oldest crops, hemp has the unique ability to lock carbon into the very fabric of the building. A further bonus is that it is actually carbon-negative too, as it absorbs more carbon while growing than is used in its subsequent manufacture – during which the captured carbon remains contained. Furthermore, the insulation is made from local sheep’s wool, and this fully multi-faceted approach minimises the embodied carbon of the development.

Economic, ecological and aesthetic – in harmony with the local environment

In terms of the building massing, the living spaces are to be organised in a human scale and rhythm over a staggered vertical section, maximising passive solar gain in winter as well as minimising overshadowing. This arrangement also allows for improved daylighting of the living spaces – the building envelope and glazing ratios were modelled by Buro Happold to establish the optimum relationship between solar gain and daylight penetration.

“The development gains on three counts from this approach,” said Young. “It is economic, saving on energy use; ecological, generating a minimal amount of carbon emissions, and aesthetic, meeting the architect’s aspirations for the scheme to reflect its local environment.”

Communal green spaces include an orchard growing local apples and a wildflower meadow

Finally, rainwater will be collected in underground tanks and used for flushing toilets and watering gardens, saving valuable resources, while swales (open, marshy drains) will deal with run-off water, as the site can be prone to waterlogging in the winter. These not only provide drainage – they also separate the pathways, play and planted areas, while mimicking the pattern of ploughed fields. The use of local clays, earth and chalk also reflect the English rural vernacular; indeed, no steel and minimal concrete will be used throughout the site.

Four communal green spaces have been created and will be open to non-residents, including a wildflower meadow, an orchard growing local apples, an allotment and a playing field.

“We are delighted that the project is meeting Orwell’s aspirations to be a forerunner in the development of sustainable affordable housing,” said Dawn Edwards, Head of Development at Orwell Housing Association.

The scheme is under construction now and should be completed this summer.