Sustainable Houses

Embodied energy/carbon

Embodied energy or carbon is the energy consumed in the construction of a house. It refers to the emissions associated with the production, transport and installation of materials, and it is incurred at construction and/or renovation, and maintenance, repair or replacement.

To reduce the embodied energy footprint, it’s important to consider the necessity of every material and its environmental impact. Before the design of the building and the material selection has been finalised, a life cycle assessment (see below) can quantify the embodied carbon in the building. If no further efficiency improvements can be made, carbon offset certificates can be purchased to achieve a carbon neutral building.

Embodied energy varies greatly with different construction types. In many cases a higher embodied energy level can be justified if it contributes to lower operational energy consumption. For example, a concrete slab floor is high in embodied energy, but it provides thermal mass for passive heating and cooling and can reduce the need for other materials.

Light timbers and woven wire balustrade screens in Halo House.

Life cycle assessment

A life cycle assessment (LCA) is a metric for analysing the total environmental impact of a material or product through every process of its life. It considers resource depletion, energy and water use, greenhouse emissions and waste generation associated with the mining or logging of a raw material through to the manufacture, packaging, transport, installation, operation, and disposal or recycling of a product.

As a building is made up of many products and materials, it is important to consider the LCA of every component in a design to ensure the building has the lowest environmental impact possible. This consideration extends to the supplier of the material or product, as they too should have a commitment to sustainable and ethical business and manufacturing practices.

Reductionism

The selection of materials or products should be guided not just by the extent of their environmental impact, but whether the material or product is needed at all. Reducing material consumption means reducing embodied energy, which, in turn, means a lower carbon footprint.

The goal of reductionism is to build less and build better. Eliminating redundant materials, such as unnecessary finishes and fixtures, not only lowers the environmental impact of the building. Removing inessential decorative items and revealing the materials underneath (see material honesty below) can be a design feature that honours and showcases the building’s key components.

Taking out unnecessary spaces (e.g. a second bathroom, a bigger car space, a separate guest bedroom or study) results in a smaller, smarter building footprint that uses less materials and consumes less energy. The savings achieved through reductionism can instead be invested into higher quality glazing, insulation, technology and landscaping that produce a better, more efficient building and more sustainable architecture.

Material honesty

The idea of material honesty implies that a material should be used where it is most appropriate, and its nature should not be concealed for the sake of aesthetics. Under the ethos of ‘perfectly imperfect’, natural imperfections are not hidden or removed but embraced, as they reveal the honest nature of the material, giving integrity to the process of construction.

Rather than covering basic components of a building (such as concrete floors and brick walls or cabling and services) with other materials for the sake of curating ‘the perfect aesthetic’, material honesty accepts and expresses the ‘true’ properties of the material wherever it is used and practically possible.

Along with the philosophy of reductionism, material honesty leads to a simpler, cheaper, healthier and less wasteful building with the added character that comes from revealing the natural properties of materials.

The flooring of Edgars Creek House is made of recycled Tasmanian Oak.

Recycled materials

Recycled materials are prioritised to extend the life of those materials and/or of buildings, and it curtails the demand for new materials, thereby reducing embodied energy and waste. Recycled materials are also more likely to be sourced locally, decreasing the emissions and costs of transportation.

Some building materials, such as bricks, floorboards and timber, can be salvaged from the demolition of an old building or sourced from a local supplier. Having developed patina from age and wear, they can contribute to the character of a new house and evoke a ‘lived-in’ look and feel.

Some building components may be made up of partly recycled materials. For example, crushed old floor and wall tiles can be made into an aggregate used in terrazzo tiles. Fly ash — a waste product of coal combustion — can be added to concrete to decrease its carbon footprint while increasing its strength and workability.

Recyclability and disassembly

While considering what goes into the construction of a new house at the start of its life, it’s also important to consider what can be taken out of the house and reused at the end of its life.

Some materials, such as brick and timber, can be used again in other buildings, thereby making the building more recyclable. Other valuable materials, such as steel, aluminium and copper, can be fairly easily recycled.

Importantly, the construction method will influence the ease with which materials can be disassembled and recycled. Glues and adhesives should be avoided, as they cause damage when materials are separated. Prefabrication and mechanical assembly make it easier to dismantle a building without destroying or contaminating precious materials that are fit for reuse or recycling.