The UK has begun experimenting with co-housing schemes that aim to slash emissions while encouraging a more sustainable lifestyle - as you can imagine, communal washing machines that run on harvested rainwater are de rigueur

The construction industry seems to be getting to grips with building low-energy housing. In the past month alone we’ve seen the completion of PRP Architects’ 10-home zero-carbon scheme in Slough, while in neighbouring Woking a 12-home development by William Lacey Group, which surpassed level five of the Code for Sustainable Homes, opened.

Although there is a long way to go to meet the government’s 2016 target for zero-carbon homes, it begins to raise the question of where you go from here if you want to drive your carbon footprint down even further. On a former farm near Gillingham in Dorset a pioneering project could provide an answer.

The Threshold Centre is one of the UK’s first co-housing schemes, which aims to slash the emissions from its buildings but also encourage a more sustainable lifestyle by addressing the carbon associated with food and transport.

Although it is still relatively new in this country, co-housing is well established in parts of North America and Europe, particularly Denmark where over the past couple of decades it has proved a popular model for delivering social housing. The idea is that individuals and families come together in communities where they each live in their own self-contained homes but also share common facilities. This enables more compact living accommodation, with less embodied energy and reduced heating requirements, and the sharing of resources such as community heating systems and car pools.

The biggest barrier for the growing number of co-housing groups springing up across the UK has been finding suitable sites and capital funding. This was no different for the Threshold Centre and having had planning refused on the first attempt, the group changed tack and went into partnership with Dorset-based Synergy Housing Association. The new proposal included plans to increase the affordable housing to 50%, a commitment to achieving an Ecohomes “excellent” rating - a planning requirement - and renting land next to the site for growing food.

Richard Swann of architect Bruges Tozer Partnership, which designed the centre, says bringing a housing association on board could help make the adoption of co-housing more mainstream. “One difficulty co-housing groups have is raising the capital. Getting the housing associations involved could help provide part of the seed funding that may tip the balance in getting groups off the ground.”

The ideal components for a co-housing scheme are a green space with buildings around the edge, an area for parking and some land to grow food. At Threshold no new build was permitted because of its rural location so 14 one, two and three-bed units have been created by reusing accommodation that had already been converted for holiday homes. Two farm buildings have also been converted while the three-storey farmhouse was a ready-made common house with a kitchen, living and dining rooms, guest rooms and space for offices and a laundry.

The big question of course is whether this approach really leads to lower carbon emissions. Data from WWF for a home built to level six of the Code for Sustainable Homes shows that space heating, domestic hot water and appliances account for 11% of an individual’s domestic carbon footprint. However, Swann says it’s difficult to put figures on the savings on this through the reduced dwelling sizes and communal areas at the Threshold Centre. This is partly a consequence of bringing the housing association on board which meant the design had to follow quality design indicators such as minimum space requirements. Also the budget didn’t stretch to upgrading the fabric of the seven existing holiday cottages.

Putting all this to one side, however, Swann says that once you have done everything you can to make the homes energy efficient, cutting an individual’s carbon footprint then comes down to lifestyle. “One of the interesting things about a co-housing group is that by having a community that shares resources you’re actually attacking some of those really stubborn problems in terms of carbon footprint like, for example, transport.” WWF estimates that transport accounts for 18% of an individual’s carbon footprint and food a hefty 23%. The car sharing scheme has proved a success. “Because they share so many things they know when other people are going somewhere so they often co-ordinate their shopping trips or get a lift to the train station,” says Swann.

The other question is how to get occupants to adopt this way of living. For most co-housing groups this isn’t an issue as they have an awareness and desire to curb their energy use.

Early assessments for sizing the biomass boiler based on rules of thumb had indicated the need for a 200kW unit, but taking the residents’ behaviour into account - combined with careful design - this was halved. And, says Swann, teaming up with a housing association has also proved to work, with a positive response from people on the housing register who were approached about living in the Threshold Centre.

The Synergy Housing Group is now working on a new build co-housing scheme and with over 20 groups on the Cohousing Network website looking for members and finance, it could be the start of something new.

Love thy neighbour

Co-housing aims to promote the benefits of informal community living, but what does this mean in reality? At the Threshold Centre there are currently about 20 people, ranging in age from two to 70. As well as sharing a common interest in all aspects of sustainability living there means contributing to the upkeep of the buildings, working in the market garden and administration work. The members also share evening meals a couple of times a week and morning meditation. Cutting carbon associated with transport is another goal and a number of residents avoid car ownership, which is helped by the car sharing scheme and other residents making their vehicles available to the group.

Cutting the site’s carbon footprint

  • Because the development is classed as a conversion, the team aimed for an Ecohomes rating, achieving “excellent” with a score of 70.5%. The converted barns have a SAP of 86 and an average domestic energy rating of 4.54kgCO2/m2/y
  • Communal spaces allow reduced individual dwelling sizes and heating demands
  • Each unit is fitted with an energy meter and all heating and hot water is provided by a central 100kW wood chip and pellet boiler
  • Space is provided for communal clothes drying
  • White goods such as fridges, freezers and washing machines are shared, saving space in the homes
  • Low-energy lighting, pump and fan loads are offset by a grid-connected 4.42kWp photovoltaic array
  • Water use is less than 80 litres per person per day. This is achieved through flow restrictors in taps, no dishwashers and two “A”-rated communal washing machines running on harvested rainwater. WCs are dual flush, and surface water run-off from roofs is stored in tanks for watering the gardens
  • The site is served by public transport and there is also a lift-sharing scheme in operation
  • The walls of the converted buildings use 300mm-thick timber stud walls filled with Warmcell insulation and clad in larch lap boarding. Reclaimed clay tiles are used for the roofs
  • Ground floors use 120mm Pavafloor insulation and birch-faced ply floating floors
  • Proposed fabric improvements to the holiday cottages will include internal wall insulation, replacement windows and installing floating floors, which could reduce the heat loss
  • by 75%.