Introduction Clay Field is an affordable housing development in Elmswell, Suffolk. In this case study, we will discuss the various strategies used for sustainable construction, lifetime energy use and landscape to achieve low levels of embodied energy and carbon emission. There are 26 houses in total, made up of 13 two-bed and nine three-bed houses, plus four one-bed flats and private gardens. The homes are grouped in threes around three communal gardens and provides remote parking courts with 42 car parking spaces. There are a range of amenity spaces including allotments, a local play area, a large football pitch and swales to manage rainwater as part of a green space strategy.
Rainwater is collected to flush toilets and to water the gardens. There are three low-maintenance gardens which are seen as part of a wider village life, a wild flower meadow, allotments and an orchard of Suffolk apples and a biomass heating system using locally-sourced woodchips heats all the homes from one boiler. The concept was to provide exemplar affordable homes which were designed to be energy efficient and sustainable, have a high design quality and provide positive public and private spaces. All homes feature extremely low embodied CO2 in construction and low lifetime energy use. The buildings make use of use a spray-on material made from a mixture of hemp and lime, which captures carbon from the atmosphere. The roof covering at Clay Field is from a renewable resource and is recyclable, as well as offering carbon captive and reduced building loads. Environmental Strategies Shelter from the elements The layout of the site provides good shelter from the wind because these properties have been built in a flat area with little natural resistance to high winds but you can see the trees and arrangements of the property groupings would provide shelter to the enclosed areas that have been created.
Rainwater Harvesting The rain is collected and used in a communal rainwater harvesting system. The total rainwater harvesting storage capacity on site is 26,000L. Each block of dwellings is supplied with a Rainsava 6,500L underground holding tank. The rainwater that falls on the roof is collected to by guttering. In the pipework before the holding tank a vortex filter has been installed to ensure no leaves and debris enter the water supply. In order to distribute the filtered water to the header tanks in each house, the holding tank has a submersed pump.
The pressurization of the pump is monitored and controlled outside of the properties, by a unit in the landlord’s shed. To prevent the water level becoming too low, the control unit also connects the header tanks to a mains cold water top up facility during low rain fall. The header tank then distributes recycled rainwater to WC’s throughout each house, as well as supplying garden taps. light (natural + artificial) The layout and orientation of the housing formation ensures that all dwelling receive maximum sunlight in different seasonal conditions despite the flat landscape. All houses face south, however the 2-storey terraces are not overshadowed by the 3-storey properties in the low angled winter sun. As a result, the houses have good daylighting. The 2-storey houses have a picture window within a deep reveal in the kitchens which gives the greatest passive solar gain.
The type of artificial lighting used in these properties would align with the sustainability and energy efficiency of the rest of the project. Therefore, artificial lighting with low energy efficiency rating such as incandescent lamps would be replaced with LED or compact fluorescent lamp (CFL) lighting. Heating & Cooling Biomass Boiler A biomass fuel district heating system is responsible for all 26 properties. The biomass which powers this communal boiler is from the local forestry. The heating system is fueled by wood pellets and has a nominal 150 – 180 kw output, using a Twin Heat CS150i automatic biofuel boiler. The heating pipework which contains, approximately 3,500L of water.
Heat exchangers have been placed in each house to control and distribute heating and hot water to the property. There are also metering facilities that are able to monitor the fuel consumption of each property remotely. The recorded flow temperature is approximately 80ºC with a return temperature of approximately 60ºC. Ventilation The houses have been designed so that the stairwells can be used for passive stack ventilation strategy. A remote-controlled powered light in the uppermost roof pitch vents the stairwell. The staggered floors have been incorporated so that the open stairwell running from the roof lights to the kitchen allows the homes can be naturally ventilated during the summer with a through-flow of air. An additional mechanical system is used during the winter which heats incoming air by using 80% of the heat from outgoing air.
A whole house ventilation system has also been designed to change all air within the property at least once every two hours. This is achieved using a network of ducts concealed within the property which extracts stale air from the Bathroom and Kitchen by using the heat recovery units inside the cooker hoods which also supplies fresh filtered air to the Living Room and Bedrooms. The properties provide warm, light and spacious homes with lower than average running costs, benefiting from solar gain in colder weather and able to be easily ventilated during summer. Human Comfort All of these environmental strategies have shown great consideration of human comfort.
Consideration of the site layout has achieved minimal visual impact and overshadowing between the properties of different sizes. This also results in a good amount of passive solar gain through the east-west orientation and south facing glazing. This also provides greater thermal comfort and less strain on the communal biomass boiler. Another factor that contributes to thermal comfort is the cooling and heating that can be achieved through the whole house and passive stack ventilation systems used, as well as providing fresh air throughout the house and a healthy home environment. Structural strategy The dwellings have timber frames that were partially prefabricated in sections off-site. The walls are raised off the ground slightly on masonry plinths to protect the timber from rising damp and there are ventilated voids beneath the timber floors.
The north and south elevations are clad in cedar boards on timber studwork battens built out from the primary frame. Elevations and roofs are clad in a continuous cedar shingles and the gable ends are finished lime render. The gable ends of the buildings are lime rendered directly onto the sprayed Hemcrete, to create an air permeable structure which offers resilience, using a recyclable product.
Variety is brought to the elevations through the different positioning and size of windows. The arrangement of the windows was determined by engineers Buro Happold, who worked out the optimal relationship between solar gain and daylight, as well as making the most of the beautiful views out. All homes get a view onto an open space and do not look onto one another. Each group of properties has access to a separate building topped with a sedum roof to use for storage. Depending on the property type, these structures are able to withstand a combination of static loads such as the live loads of the occupants and the dead loads of the structural elements as well as the positive and negative wind loads. The distribution of the loads travel from the roof through the exterior and interior walls and the floor into the substructure and foundations where it is transferred to the supporting soil. Construction strategies To maintain the sustainable aspects of the scheme, an early decision was made to use cedar shingles on the sloping roofs.
However, the cedar shingle roof constituted a risk for spread of flame so the rafters have been overdrawn with a layer of calcium silicate board to provide 30-minute fire protection. Isonat, another hemp-base product made with recycled cotton fiber and a thermoplastic binder has been used to insulate the roof. Sedum roofs are a high performance single layer felt which provided waterproofing to the flat roofed store areas, and is overlaid with insulation, deck, protection fleece, drainage layer, substrate and sedum planting to provide an ecological protection layer which improves the surrounding air and water quality whilst further lowering carbon emissions and sustain a wildlife habitat. The dwellings have timber frames that were partially prefabricated in sections off-site. To brace the frame of the walls 12 mm Sasmox sheathing, a gyspum reinforced fibreboard, was fixed on the inside. The walls were insulated with Hemcrete, a mixture of hemp, hydrated lime and a small amount of Portland cement as a binder to accelerate the curing process to set a rigid, breathable layer. The Hemcrete was mixed on site and sprayed onto the timber frames to ensure there are no gaps that might compromise air-tightness. The use a prefabricated element ensures that the time to build is less however there would be an increase in cost and a greater need for specialized workers during construction.
On the gable walls the Hemcrete was finished with 20 mm of lime render. The window openings on the gable were lined with 25 mm Heraklith wood fibre boards to form a square reveal and the lime render is returned into the reveals. Curved walls provide privacy and enclosure to the gardens. They are built from unfired clay blocks rendered both sides with lime render and capped with a cedar shingle coping. Energy Rating and Energy Consumption All 26 properties feature a number of environmental, structural and contractional strategies that ensure that it was an energy-efficient build with low CO2 embodied during construction and low energy use during occupation. The highly insulating hemp material (Isonat) which consists of minimal perforation, reduces the heat loss from the north facing facades as well as capturing carbon from the atmosphere, making it a less than zero carbon material.
The communal biomass heating system that heats all the homes from a single boiler only using locally sourced wood chips as fuel, and rainwater recycling system are all examples of the innovative energy conservative solutions implemented in Clay Fields. The energy consumption of any artificial light needed is minimized as well by the amount of natural light that fills the homes. In terms of energy rating, the so that the artificial light that is used still doesn’t have as great of an energy consumption and keeps energy bills low. The residents have been provided with tips like when to and when not to open windows. This further reduces the energy consumption by lessening the need for the boiler. Overall, the project achieved an EcoHomes ‘excellent’ rating and obtained a grant from the Low Carbon Buildings Programme.