Currently the building industry is looking toward sustainable buildings as the future of construction, because that is what the market demands, but also because of potential cost savings to them in materials and maintenance. Trying to define sustainability is a difficult task, and you will likely get as many varied answers as people you ask. There are some key points that tend to overlap to give us a workable definition from which to start, and balancing these factors is the key to a sustainable approach.
Sustainable concerns are largely a result of environmental considerations. How much can we take form the natural world before it gets irreparably damaged. The range of opinions on that question is huge, but we tend to think about the environment in terms of resources. All of our needs come from sources in the environment, some are renewable, such as timber and food, some are non-renewable, such as iron and coal. While we can process and recycle iron, we can only use coal once, which makes it less sustainable than iron, for example. This is a simple way of looking at the environment, and skims over issues such as old growth vs plantation timber, but old growth timber is rarely used in modern construction.
Any definition of sustainability must necessarily take economics into account. Not just broader economic questions of productivity and economic growth, but the real-world cost of making and building things, and the cost of maintaining them throughout their useful lifespan. It also needs to be considered how long that lifespan is. A house made of wood may be relatively cheap to build, but ongoing costs such as painting must be factored in, and the total lifespan of wooden buildings is considerably less than brick or concrete constructions, though of course, the material itself is renewable within the lifespan of the building. The question of what is a more functional building is a further consideration, which relates to the final factor to consider.
In most parts of the world, humans need houses to at least sleep in, for at least part of the year. They need workshops and schools and offices, and hospitals as well to maintain or improve their standards of living. Beyond basic utilitarian functions of the buildings, aesthetics and personal preference will also play a role in selecting and constructing buildings. A concrete building may be cheaper and longer lasting, but people may prefer an older-style wooden house to a concrete box.
What are sustainable building materials?
Sustainable building materials have to fulfill a number of criteria
- Wherever possible be from renewable sources
- Recyclable or reusable materials are preferable
- Low energy input in material manufacture
- Use as little water as possible in manufacture of materials and construction
- Preferably low maintenance/after-construction care of building
- Provide good thermal qualities to the finished building
- Provide suitable structural properties for the application
There are good economic reasons we see less building being constructed that resemble older style timber buildings, but some older building materials offer good sustainable properties
Timber is a renewable resource, and can be readily sourced from sustainably managed forests and plantations. It is light and easy to work with for professional builders, and requires little in the way of specialist equipment beyond standard carpentry tools. The major drawbacks are that it does deteriorate over time if not carefully maintained by staining, oiling or painting. This adds a considerable amount to ongoing costs of timber buildings. Timber buildings are not well insulated, but can be okay if thermal insulation is installed between the external timber wall and the internal plasterwork. Due to the low load-bearing capability of timber walls, the roofs of timber buildings are often of corrugated metal, a non-renewable material which has long life, but poor performance as an insulator. It gets very hot in summer and cold in winter.
Brick, clay and concrete
Bricks do come from a non-renewable source, as clay is dug out of large pits and fired into bricks, while the components for concrete bricks are also mined in various ways. But they are reusable – should a building be demolished, the bricks can be cleaned and reused as new building material or as paving. There is also a large amount of “embedded energy” in clay bricks from the mining and firing processes. The longevity of brick buildings is much greater than for timber, and while there are some issues with the thermal properties of brick veneer buildings, double brick or “cavity brick” buildings have excellent insulating properties. The greater load-bearing strength of brick walls means roofs can be constructed of heavier materials such as slate (a non-renewable material) or terracotta tiles. Terracotta is also a clay-based material, and is again non-renewable, but it is long lasting and provides greater thermal insulation than metal roofing materials.
So called “mud” bricks are generally constructed onsite using the available soil. This method is also called “Adobe” in some parts of the world. Some soils are more suited than others for this purpose; usually a clay content of between 30% and 70% is required to make cohesive bricks. Such soils are present over large regions of Australia, so many areas are suitable for mud brick building using materials sourced on site. The low energy inputs for material transport and construction are the big attractions to mud brick, as bricks are formed and dried on site using only natural energy from sun and wind.
Mud brick buildings surprisingly don’t have good thermal insulation properties, due to the lack of air space in the walls. For this reason walls may be lined internally, as with brick veneer buildings, or externally, so-called “reverse brick veneer” in order to create such an air gap. As walls are generally thick to provide stability, they tend to have good load bearing properties, though in Australia extra framing is usually incorporated in the design, but roofing options are quite broad. While mud brick buildings in Australia are generally kept to single or double storeys, there are mud brick constructions around the world up to 8 storeys high that have stood for centuries. One of the major attractions to mud bricks is that if the building is ever abandoned or past using, all fittings can be removed, and it basically returns to the site as soil. One drawback of this is that it does require maintenance through its lifespan to prevent the bricks from literally eroding. This can be done by coating with a render, which may be something relatively permanent such as cement or something less stable like mud slurry or lime wash.