In response to the growing consumer demand for sustainably conscious housing, a number of different sustainable, ecological, eco-friendly, or low-energy housing options have been created. With eco-homes, such as the Osborne Demonstration House in Watford, developers seek to make individual single-family homes more energy efficient using innovative architectural design and start-of-the-art appliances (Appendices F, G, H; Energy Saving Trust, 2007; Osborne, 2006). Green construction schemes like Millennium Green in Nottinghamshire, extrapolate the concept of the eco-home to an entire housing development (Appendices I, J, K; Freerain, Ltd., 2007; Sponge, 2005). Bed ZED in London is an example of a large sustainable development that features energy efficient homes, community facilities, and workspaces, trying to amalgamate sustainability, notions of “living a green lifestyle,” and new urbanism (White, 2002). Tinker’s Bubble in south Somerset, a low-impact settlement, takes a different approach to green living by minimizing the ecological footprint of the development and its residents.
This report examines a recently constructed sustainable housing development in the UK, the Hockerton Housing Project (HHP). The first section presents a description of the selected project with photographs and sketches. The second section discusses the sustainable characteristics (features of design and materials selected) of the development and building structures. The last section offers the results of the sustainable efforts. Attached appendices feature sketches, design specifications, photographs, and other pertinent information for the HHP and two other sustainable projects, the Osborne Demonstration and Millennium Green.
The HHP is located on a 10-hectare site outside of Nottingham in the United Kingdom. The development was self-built, meaning the occupants were responsible for planning, design, and construction, not a professional developer. It claims to be “the UK’s first earth-sheltered self-sufficient ecological housing development” (HHP, 2007). The overriding objective of the development has been to be autonomous with net zero carbon dioxide (CO2) emissions, while being comfortable and requiring minimal maintenance. As an autonomous development, HHP would be responsible for creating all of its energy and recycling its water and wastes. Achieving net zero CO2 emissions would help reduce greenhouse gases that cause global warming. Figures 1 and 2 show different views of the HHP.
Hockerton homes were created with a number of characteristics that encourage the sustainability of the development. Particular regard was given to the features of design and construction materials to achieve the development’s goals.
Features of Design
The HHP was designed to consider the entire community as well as individual units. Site planning was considered ecologically friendly by including such features as a reservoir, earthen bund, gardens, and water features. Appendix A shows a map of the Hockerton site. In keeping with the development’s green living ideals, an organic vegetable growing area and garden, available for use by all residents, is supplied with water by an adjacent duck pond. The bund, a manmade earthen hill, is located at the edge of the property to reduce noise and visual impacts from the nearby road and act as a basin for an adjoining reservoir. A manmade lake and watering pond were built to encourage biodiversity and improve the visual appeal of the property.
The site plan was partially dictated by the water supply and sewage system, shown in Appendix E. Wastewater flows from the homes to sump and septic tanks hidden food growing beds. A reed bed system in the corner of the lake processes wastewater from the tanks “supplying oxygen to bacteria in the water, which digests the pathogens in the sewage” (HHP, 2007). The reservoir is the storage for non-drinking water collected from rainfall, fields, and runoff, which have been filtered through a sanded area.
Individual units at Hockerton were designed so that each component provides sustainable benefits. Appendices B and C feature sketches of an individual modular unit. Each home currently accommodates as many as two adults and three children. Designing the homes as repetitive modules reduced construction costs as well as simplified the construction. As of 2005, there were five single storey homes on the site. Each home is six meters deep and 3.2 meters wide. Outside each unit is a 19-meter south-facing conservatory (to maximize sunlight) and inside is 3-meter high French windows, which allow natural light into the units while stabilizing the indoor temperature during the winter. Windows are double and triple glazed to improve the home’s insulation and increase energy efficiency. A mechanical ventilation system (not central heating system) inside the house circulates air.
A key feature of each unit is its earth sheltering. After construction, five hundred tons of dirt was placed on the roof, rear wall, and two end walls (HHP, 2007). Much of this dirt was displaced by the construction and earth sheltering was a way to integrate it back into the site, minimizing the green footprint of the development. The green footprint is the amount of environmental resources consumed during the creation and operation of a site and required to processes the residents’ wastes (Reed, 1992). The earth sheltering also has become a home for grasses local wild plants, frogs, and butterflies. Additionally, the soil provides good insulation and helps to stabilize indoor temperatures.
The renewable energy system is designed to utilize both the site and individual units, as shown in Appendix D. On the roof of each home are photovoltaic arrays that absorb solar energy and convert it to electric power that is then used inside the home. Wind turbines on the site also generate energy.
According to the HHP (2007) team, a number of factors influenced the selection of building construction materials. Minimal embodied energy, the total amount of energy required to produce, use, and dispose of a product, balanced by long-term energy savings and minimal impact on land and resources were paramount concerns.
Each unit was constructed on a 300-millimeter concrete slab. Internal walls were made 200 millimeters thick and the external walls 500 millimeters thick. Each roof is concrete beam and block. Concrete was chosen as a primary construction material for several reasons. Most importantly, concrete has a high thermal mass. Thermal mass is the measure of a material’s ability to store heat (HHP, 2007). The higher the thermal mass, the greater the ability of a material to store heat. A home of high thermal mass construction is able to absorb heat, hold it for long periods of time, and then release it slowly. Heat may come from sunlight (maximized by the design of the units), body heat of the occupants, and electrical appliances. Hockerton homes can even soak up heat in the summer and release it in the winter. High thermal mass construction leads to temperature stability. In the HHP, concrete construction has eliminated the need for a central heating system or any secondary heating (e.g., space heaters) and thereby decreased energy consumption. In addition, concrete was used because it is inexpensive and widely available.
Figure 3 shows some of the other eco-friendly materials were used in the construction of the Hockerton homes. Floors are clay tiles because they require less energy to produce and are cooler in the summer than carpet (Energy Saving Trust, 2003). Wood was purchased from sustainable timber sources. Environmentally friendly, low volatile organic solvent (VOC) paints were used. High VOC chemicals vaporize easily, can be hazardous to human health, and contribute to smog. Kitchen units, furniture, and other household items were made from recycled materials when feasible.
The Sustainable efforts of the HHP seem to have yielded positive results. Figure 5 compares the energy usage of homes at the Hockerton development to that of conventional housing and homes built under zero heating and zero CO2 schemes. Hockerton homes consume one-third the energy of conventionally built housing units and about one-half the energy of zero CO2 homes.
Through the use of innovative design and high thermal mass construction materials, Hockerton creators have been able to stabilize the indoor temperatures of the homes, adding to the units’ energy efficiency and the comfort of the residents. Figures 6 and 7 show the temperatures in the bathroom, kitchen, conservatory, and bedroom during cold and warm weeks. During a cold week when the outside temperature is from -5°C to 10°C, the temperatures of the internal rooms are nearly stable at 16°C. This indoor temperature stability is impressive considering none of the housing units have central or secondary heating systems (HHP, 2007). During a warm week when the outside temperature is from -10°C to 35°C, the temperatures of the internal rooms average 25°C. The units’ orientation, well-ventilating design, and self-shading additions (e.g., blinds) reduce sun glare and the amount of heat entering the homes.