The physical structure of sustainable homes are likely to be smaller and simpler but sufficient to provide families with the maximum well-being. There are a range of factors that affect the sustainability of a dwelling including type, size, shape, position, materials and construction method.
Sustainable homes are ones that create the most well-being – comfort, security, privacy, health – whilst having the smallest possible ecological footprint. Everybody is different and would like different things from a home. In the past century, whilst there has been cheap and abundant energy, houses have become larger and more complex, although there is little evidence that this has made people happier. There is a strong case for thinking that smaller, simpler, more affordable homes are much better for people, as well as for the planet.
The factors that make the physical structure of a home sustainable or not are:
- position, orientation and location
Type refers to whether your home is an apartment in a block, an attached house (e.g. a row house), a semi-detached house, an apartment or flat within a detached house, or a fully detached house. In general an apartment is going to be much more sustainable, because it has a smaller ecological footprint, than a detached house, even if it has the same floor area.
The size of a dwelling significantly affects the size of its ecological footprint. House size affects the amount of materials and embodied energy in a new house, as well as the amount of materials and embodied energy to maintain the house, and the amount of energy used to heat, cool and light the house.
Average home size varies throughout the world. The average new house in New Zealand is a whopping 209m2 compared to the average UK home which is only 76m2 and in Hong Kong it is a meagre 45m2.
The larger the house, the more embodied energy it has. Embodied energy is the energy that was required to build the house including the manufacture of all construction materials, components, fixtures and fittings.
The amount of energy required to heat a space is a also a function of the size of the space. Approximately 60% of the power used in the average home is used for space heating. In theory halving the size of a house size will decrease your energy consumption by a third.
The amount of energy used in a house is also a function of the number of people who live in it. In many western countries there are fewer people living in houses than ever before. For example the average household size in New Zealand decreased from 2.8 people in 1981 to 2.4 people in 2006. It is projected to decrease still further to 2.3 by 2021. There are a number of reason’s why average household size has decreased and continues to do so. There was a trend throughout the twentieth century from larger, extended families to smaller, nuclear families. Also people live longer now on average and there has been an increase in the number of widows and widowers living alone.
Big houses don’t make people happy. As the cost of building and maintaining bigger houses has steadily increased people are looking for other housing options. The obvious solution is to build and live in smaller homes. A small house is cheap to build, heat, cool and maintain, it is quicker and easier to clean and it is much more environmentally friendly. So you can be just as happy in a small house, if not happier.
House construction and materials
The way a house is constructed and what it is constructed out of also affects the ecological footprint of the house. Construction methods vary from place to place and they have evolved over time. The availability of materials locally and the prevailing climatic conditions have traditionally had the largest part to play in the construction of long term shelters. Before the agrarian revolution humans were always on the move. They made shelters out of a wide range of materials including wood, skins, canvas, snow, earth, ferns, grasses and turf. Once humans started farming in the same place year after year they started to build permanent shelters. These shelters were made out of materials found locally including wood, bamboo, straw, earth, grasses, mud, clay, stone, sand and cement. As technology became more sophisticated construction techniques became more standardised but also more complex. The construction of permanent homes went from being a skill that all people knew and practiced to being a specialist skill that you need to pay someone else to do. In all parts of the world you can find wood-framed bungalows and the wood doesn’t necessarily come from anywhere near. An obvious case in point is that most Inuit live in wood framed bungalows in places where no trees grow. Ideally building materials should be locally quarried or grown.
The wood frame house is permeable, unlike a rammed-earth house for instance, and must have insulation added to increase its thermal performance. A heavily insulated house, wood-framed or not, will be much warmer in winter and cooler in summer than a house that isn’t. This means that it will take much less energy to heat or cool it to a comfortable temperature when necessary. The Passivhaus standard describes one of the most energy efficient house construction methods.
House shape is predicated on a number of factors. However the fundamental rule is that a simple shape is much more sustainable than a complex shape. Complex shapes use more materials and they are not as energy efficient because they have more surface area. The shape that uses the least amount of materials is the circle. Traditional circular shelters include igloos, teepees, African mud brick huts, yurts and British and European roundhouses. They were the shape of choice because they were strong, energy efficient, good for ventilation and air circulation, less vulnerable in strong winds and they used the least amount of material in relation to floor area. After circles, squares are the most efficient shape, then rectangles.
House location, position and orientation
The location, in terms of climate, is an important factor in the design, construction, and therefore sustainability, of the home. Houses should always be designed to require the least amount of materials and resources as possible to suit their location.
Orient the house and windows to ensure it gets the most amount of winter sun. The house could also be positioned on the property to get the most shelter from cold wind and summer sun.