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
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.
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.
Shelter from the elements
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.
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
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
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
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
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
Heating & Cooling
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
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.
have been designed so that the stairwells can be used for passive stack ventilation
strategy. A remote-controlled powered
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
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
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.
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.
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
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.
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
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
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
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
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.