As long as there are people, there will be a need to build. At some point in the past, our need for housing outgrew the availability of caves, not to mention the geographic inconvenience of living only where they could be found, they were not very good at keeping people warm and dry and safe. Especially as numerous other animals wanted to live in them too. As the population grew, there were as many approaches to the problem of shelter as there are different cultures in the world.
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.
A variation on mud bricks, rammed earth uses onsite soil mixed with gravel or sand which is then poured into wooden or metal forms and pounded down to form solid walls. This is quite a flexible system of construction, and is limited only by the shape of the available formwork. The properties of walls are similar to mud bricks, and have the same drawbacks as far as weathering and insulation properties. They do need to be treated to prevent water and wind erosion. Both rammed earth and mud brick buildings can be extremely fire resistant, depending on other fittings like doors and roofs, so may be a good choice for fire-prone areas (rebuilding houses frequently is far from sustainable). Cob construction is a similar method but uses no formwork, so the density of walls is less, and they are usually constructed including straw, which does give a level of insulation to cob walls.
Like the name says, straw bale construction basically uses bales of hay or straw like giant bricks to build walls. The walls are then covered with a render to prevent moisture entering and rotting away the bales. This also stops potential fire hazards and also keeps rodents and vermin out of the straw where they could otherwise nest and cause problems with structural integrity. Footings need to be well-constructed for these types of buildings, and they are generally limited to a single level due to stability of the walls. Straw bale buildings have generally good thermal insulation, and straw itself was once commonly used as an insulating material before synthetic materials became widely available, which don’t attract hungry animals. Roofing options can be somewhat limited without extra framing, though this is commonly incorporated.
Traditional building methods and materials have given us our inherited aesthetics about what a building should look like. But those appearances are often linked to the limitations of the materials themselves, and more recently developed building techniques have opened up the possibilities for constructing buildings of almost any shape.
Steel and concrete
The increasing use of steel and concrete in construction is primarily an economic one. Materials can be purchased in bulk, and used on any project of pretty much any size as required. The most common way to use these materials is by pouring concrete around steel reinforcing mesh in a formwork, then attaching the formed walls to a steel framework. This may be done onsite, or prefabricated concrete panels can be transported from a manufacturing plant.
The benefits of such a modular building method are primarily in the construction phase, allowing buildings to be completed in a very short amount of time by relatively few people. The machinery involved has a generally high initial cost, and these methods are generally confined to large projects rather than domestic home builders. The materials themselves have similar thermal properties to earth walled buildings, and concrete walls usually require lining with insulation to make them habitable. This method of construction allows radical departures in building shape form those offered by traditional material, but the visual appeal of many modern buildings is highly subjective.
There are numerous specific building products available, including specially designed materials that behave like brick or concrete in construction and durability, but have enhanced thermal insulation properties. Such products may be manufactured using wood waste or other materials such as polystyrene as a base, or even aerated concrete, manufactured using various industrial processes. The sustainability of these materials is widely variable, so each material should be considered individually. The questions to be asked of any building material are those listed above – basically, where does it come from, is it renewable, how long does it last, and how much maintenance is required throughout its lifespan?
Improving sustainability of buildings
Besides the materials to construct the actual building, there are ways of constructing more sustainable buildings through design, or including additions that can help reduce the environmental footprint of a building. They can also potentially help out on the economic side of things by reducing ongoing costs.
Passive solar design
There are ways of designing buildings to make use of the elements themselves to maintain a comfortable living environment. In temperate parts of the world, the sun changes its angle in the sky between winter and summer. In Australia, placement of windows on the north side of buildings captures more winter sun, warming the air inside the house. Conversely, fewer windows to the south mean less heat loss, as no direct light ever comes form that direction. Thermal mass floors and walls of brick, earth or stone inside the rooms facing north will help capture some heat during the day and release it night.
North-facing verandas at the right depth will allow winter sun in, but keep summer sun out when the light comes in at a steeper angle. In more tropical climates, a veranda all the way around the house will contribute significantly to cooling, as will strategically planted vegetation. In many parts of the country, the temperature drops significantly when the sun goes down, and it’s often easy to incorporate flow through breezeways internally that allow the building to be opened up when a cool change hits. This way the building can be comfortable again quickly without resorting to expensive air conditioning systems.
Catching solar energy
Photovoltaic panels or solar hot water systems can significantly reduce reliance on non-renewable energy sources. The initial outlay for solar panels may be relatively high, but the cost of electricity is increasing quickly, and panel efficiency is improving – so the economics are becoming more attractive each year. A good solar hot water system can save energy too by heating water when the sun is available, and storing it for use at any time. Most systems come with a booster for when the sun doesn’t shine. The way these kinds of things are calculated is usually to compare the cost of the equipment, installation and maintenance to the price of buying electricity or gas for hot water. If the money saved exceeds the cost of the improvement over a period less than the lifespan of the system, it’s worth thinking about. For example, if a solar electric system that lasts ten years costs $5000, and you would reasonably spend that much on electricity in only 5 years, it’s a good deal.
Water is also increasing in price, and with many states in Australia having experienced water restrictions in recent years, catching some water from the roofs of buildings seems like a good idea, especially if gardens and vegetation are part of a sustainable design. Of course it’s easier to design water catchment facilities before a building is constructed, so storage can be incorporated into the building itself, but there are novel and unobtrusive ways of introducing water storage into landscapes and even under existing buildings. There are drawbacks though – all water catchment needs to be accounted for. For example, storm water drains are calculated to operate with a certain flow through of water each year, with a particular peak flow that cleans them out once in a while. If water is taken out of the system before it reaches the storm drains, cleaning them out may mean someone has to get in there and do it. In some cases, water companies will continue to charge fees for this kind of service even if you don’t buy your water from them. It’s worth checking into with water supply companies in your local area.
Green roofs and walls
Another idea that is taking off is the use of plants directly on buildings to help insulate them against heat and cold. On existing buildings, special materials need to be used to provide planters and growing medium for plants, but new buildings could be designed to incorporate green roofs and walls into the construction phase. The main consideration is the weight of growing material and plant matter that can be supported by the roof. These designs are usually based on only using available rainwater for the plants, with no additional irrigation, so plant selection is often limited to succulents and plants indigenous to a particular area, as they are adapted to the average rainfall. Of course, the layer of growing media on a roof is not quite the same as the depth of soil in the ground, so some adjustments may need to be made to any plant selection for rooftops.
Finally – ask questions
When trying to source sustainable materials and include sustainable options in new buildings, or even for retro-fitting old buildings, the key is to keep asking questions. If you are serious about sustainability, always find out where your materials come from, how they are produced, how long they will last and what happens to them when they need to be replaced. Sometimes what appears to be a more expensive option in the short term becomes a better investment down the track than when a cheaper item needs replacing. Possibly the key to sustainability is to buy less stuff, so buying high quality materials to begin with is a step in the right direction.
One of the big motivating factors to build sustainably in today’s market is to approach energy use judiciously. Part of the process is to select an energy provider with competitive price points. Rather than sticking with a known entity or default provider, shop around and look at the finer detail of what’s on offer. Compare energy providers today and save sustainably.