The third Permaculture Design principle is ‘Each Important Function is Supported by Many Elements’.
The key focus of this principle is to:
- Identify which functions in the design are critical – such as water, food, energy, fire protection, and
- Ensure that these critical functions are supported in two or more ways
Firstly, the whole point of identifying which functions are critical is so that they are adequately addressed in the design.
While this may seem like common sense, if this point is missed, the consequences can be disastrous to say the least. By formally addressing this step, we create a checklist of what we need to pay important attention to, so nothing is accidentally left out.
One of the largest flaws in a design would be to not address critical elements on which the success of the design depends.
Secondly, the reason for ensuring that critical functions are supported in two or more ways is essentially that of resilience.
A resilient design is one where the operation of critical functions continues if any one system were to break down.
By building multiple systems to support one function, we eliminate any weak links in the design. There is no single point of failure, so our system has a higher chance of continuing to run should any unforseen circumstances arise.
So, what functions are so important that we need to go to this trouble over in our designs? Let’s have a look at the in more detail:
A. Function – Water
The most important is Water. This is the very substance that supports all life, without it, nothing lives. This is a good place to start.
In an urban Permaculture design, unless the property is ‘off the grid’ so to speak, we already have mains water supply. This provides a source of drinking water for people and pets, water for washing and cleaning, and irrigation water for the garden.
The garden also naturally receives rainfall, which, depending on rainfall levels, may be sufficient to sustain the garden without supplementary mains water irrigation.
In this scenario, if the mains water supply was cut off, contaminated, or restricted, both people, animals and garden may be in trouble. Even though the garden may possibly survive on just rainwater falling directly from the sky (if there is enough of it), as it has two water sources, the household has no other water source, other than mains water supply – the single point of failure.
We can make the system more resilient by harvesting rainwater from the roof and storing it in a water tank. This captured rainwater can be used for washing, flushing the toilet, or even in the shower. If the rainwater is run through a water filter, such as a reverse osmosis/activated carbon filter, it can provide the household with pure, clean drinking water for drinking and cooking. Now the household has two sources of water, rather than just one.
It doesn’t have to stop there, for we can still install a wastewater recycling system if we really want to go to the trouble to capture wastewater from the house and purify it to a level where it becomes potable water fir for human consumption. If we do that, we end up with three water sources for the house alone.
The rainwater stored in the tank can also be pumped into the garden, providing the garden with a third source of water, the other two being mains water and direct rainfall. Once again, we can take this a step further and install a greywater system that pumps dirty water from the kitchen and laundry to our shrubs and trees (you should never direct greywater into garden beds where vegetables are growing, as the water contains high levels of bacteria and will contaminate the food and make you sick!) By doing this, we have now added a fourth water source for the garden.
I’ve illustrated a simplified version of this below:
Here we can see that the brown drip-line irrigation feeds both the main garden beds, and the tree/shrub areas.
We can select the water source that runs into the drip-line irrigation, we can either run mains water from the tap, or we can pump rainwater from the tank.
The greywater from the kitchen and laundry can only be directed into the tree/shrub area, but this area is also fed water from the mains/rainwater drip-line system.
NOTE: I’ve stated that this has been simplified to illustrate a point – please note that kitchen water is technically classed as blackwater, the same class as toilet water, as it contains very high levels of bacteria, because it contains food waste. You would not direct kitchen water into your greywater system, it would in reality go into a separate waste treatment system that treats sewage.
This illustrates the range of sources (elements) that we can use to provide water (function) in an urban permaculture design.
In a larger scale rural design, we get many more options.
In addition to the water sources already mentioned:
- Mains water supply (if present)
- Rainwater tanks
We also have many other additional water sources such as:
- Rivers and creeks
- Irrigation channels
- Sewage treatment systems
Here is an illustration of the above-mentioned water sources in a rural setting:
Furthermore, we have ways of capturing more of the natural rainfall using the following methods:
- Swales (contour trenches)
- Chisel plough (Yeoman’s plough)
Natural rainfall can often flow across and over sloped ground rather than soak into it. We can enhance the ground’s ability to soak up more water by using contour trenches, which are called swales in Permaculture. We can also use chisel ploughs to help the soil absorb more water.
With swales, the dirt removed from the trench is banked up on the downhill side to create a swale mound or embankment, called a berm. The berm is usually planted up with ground cover plants, and nitrogen fixing plants. When these plants are established, the fertility of the soil is improved, and then a row of trees (usually food producing) is planted there. The water soaks past the tree roots as it moves down the slope through the depths of the soil. The swales will also collect any soil that is being eroded from the slope, and slow the flow of water down to dramatically reduce soil erosion.
Chisel ploughs are used to break up compacted soil without turning it over and disrupting the soil structure. By cutting narrow channels around 30cm deep in the soil, we improve drainage, aeration and water penetration in the soil. This also keeps organic matter on top of the soil, where it can break down to form a useful mulch, and therefore prevent erosion of the soil.
B. Function – Food
Another important function that we need to pay attention to in our designs is Food.
As the issue of food security becomes more prevalent in our world of energy decline, peak oil, and growing urban populations, we look to resilient food sources to address the matter.
Once again, we are looking to create a system with built-in fail-safes, where we can continue to have a reliable source of food if one source fails.
The criteria for designing resilient food systems is that they must be able to:
- Provide a consistent supply of food throughout the year (throughout all four seasons – summer, autumn, winter and spring).
- Provide a range and variety of foods (such as leaf and root vegetables, fruits, berries, nuts and grains).
- Provide the required foods from multiple plants or trees (for example growing two or more of one type of fruit tree , so if you lose one, supply of that specific fruit is maintained).
- Provide the required foods though different varieties of the same plant or tree (for example, growing several varieties of corn, so if one variety succumbs to pests or disease, the resistant varieties survive).
Provide a consistent supply of food throughout the year
Several strategies can be employed for ensuring that food is produced all year round, these work by extending the harvest season.
Firstly, with fruit, we can take advantage of the fact that different fruit trees bear fruit at different times of the year.
By planting fruit trees that bear fruit in summer, autumn, winter and spring, we can have an abundant supply of fruit all year round.
As a rough guide, here are the seasons when different temperate fruit mature and are ready for harvest:
- Apples – summer to autumn
- Pears – summer to autumn
- Peaches/Nectarines – late spring to mid-autumn
- Plums – late spring to mid-autumn
- Cherries – late spring to mid-summer
- Apricots – late spring to mid-summer
- Persimmons – late autumn to early winter
- Loquat – late winter
Another way of extending the harvest season is to plant different varieties of the same fruit tree, which all bear fruit in different months, to ensure a long productive run of a specific type of fruit.
Therefore, instead of planting one variety of a specific fruit tree which will bear fruit for a short period of time, we can use early season, mid-season and late season maturing varieties of the same fruit tree to extend the harvest season over many months.
For example, to be able to harvest apples six months in the year (from mid-summer to early winter), we can plant:
- Early season apple varieties – for mid to late summer fruit
- Mid-season apple varieties – for early to mid autumn fruit
- Late season apple varieties – for late autumn to Early winter fruit
We can also extend the harvest season of vegetables too, but this requires a very different approach. Since many vegetables are annuals, and have very specific seasonal requirements for their growth, the only way to extend their productivity is to replicate their required conditions. Here are some ways to do this:
- Plant vegetable seeds much earlier than usual – start vegetable seedlings indoors a few weeks early, in a warm spot inside the house like the top of the refrigerator, then, when they sprout, move them to a warm spot near a sunny window. This will give them a few weeks head-start, so they will bear earlier in the season, and for longer.
- Use a greenhouse. A greenhouse traps the sun’s heat to maintain a temperature several degrees higher than the outside air, and retains this temperature for a longer period into the night, as the air temperature drops outside. A greenhouse also maintains the warmer daytime temperatures throughout the cooler seasons. It can therefore be used to start seedlings earlier, but the main advantage of a greenhouse is that the plants can continue growing long after the plants growing outside have died down from the cold winter temperatures. This extends the productive season of the plants grown in the greenhouse, even allowing multiple crop harvests from the same plants.
Use of Annuals and Perennials
Furthermore, by planting both Annuals and Perennials, you have greater resilience with your food supply.
Annual plants require more work to grow, have a fast growth spurt, and require large amounts of nutrient in a short space of time. They also yield seeds which can be used to sow more annuals in the following years, and they can be left to self-seed.
Perennial plants have slower growth rates, and either persist through all seasons, or die down above the ground only, while the roots remain active and burst forward with new growth in spring. These can seed, or can be propagated by division in many cases, yielding more plants which can then be used to extend the garden and its food producing capacity.
By employing both annual and perennial plants, both of the plant growth and survival strategies are utilised in food production, maximising the garden’s resilience to adverse conditions and crop failures.
In rural setting, food for livestock is also very important. Here we need a combination of annual perennial forage crops as well as trees that can be fed to livestock.
Fodder trees include varieties such as honey locusts, poplars, tagasaste and willows.
Provide a range and variety of foods
For human sustenance, a variety of foods are required to ensures that the range of nutrients that are required for maintaining health are obtained.
The common varieties of foods are leaf and root vegetables, fruits, berries, nuts and grains.
At the risk of stating the obvious, the wider the variety of foods grown, the more resilient the food supply. By having various sources for any specific nutrient source, if you lose one variety to pests, diseases, weather or any other unfortunate circumstance, there are many other sources left.
For example, as a source of magnesium, we can use:
- Leafy greens – spinach or Swiss chard
- Seeds – pumpkin seeds or sunflower seeds
- Legumes – soy beans or kidney beans
- Nuts – brazil nuts, cashew nuts, almonds or pine nuts
- Other – artichokes or okra
Similarly, when it comes to sources of calcium, we have a choice of:
- Fruits and berries – blackberries, blackcurrants, dates, grapefruit, mulberries, orange, pomegranate, prickly pears
- Vegetables – amaranth leaves, bok choy, brussel sprouts, butternut squash, celery, Chinese broccoli, French beans, kale, okra, parsnip, Swiss chard, turnip
- Nuts – almonds, amaranth, brazil nuts, hazelnuts, pistachios
Not that we choose our foods by the nutrients we want to derive from them, but in the case of this example, if you grow many of these foods, your body won’t run the risk of magnesium or calcium deficiencies. Even if some of the plants fail to yield any produce in any one season, as you’ll draw the required nutrients from all the other sources available to you.
Provide the required foods from multiple plants or trees
This is a rather straightforward concept, if you critically depend on something, keep a spare! By having more than one of this design element, if you lose one, you still continue on, just with one less.
For example, if you’re growing apricots because you depend on dried apricots as a fruit source over winter when there’s not much around, you’ll be in trouble if something happens to that one apricot tree you so dearly depend on. Sure, you could replace it, but it will be several years till the new tree grows to size and establishes itself to provide the same amount of produce.
So, if space permits, instead of planting one apricot tree, plant four! Not only do you now have four times the produce – real abundance, but if by some chance you lose one tree, you only lose 25% of your apricot production, rather than all of it.
But depending on one single variety has its own inherent risk, as some pests or diseases may attack one variety of a plant or tree and not another, so to build even more resilience in our food supply, we can take a further step, which leads us to our next strategy.
Provide the required foods though different varieties of the same plant or tree
This strategy is very important when growing key staple foods that you depend on, such as wheat, rice, corn and so on. Many communities in the past have learned to use different varieties of their staple food source plants to ensure that they don’t face starvation should one variety fall prey to pests or disease.
For example, corn or maize has been cultivated in Mexico for 5000 years, it was first domesticated in Mexico’s Sierra Madre region around 3,000 B.C. It is one of the three most important staple food crops in the world. The other two are rice and wheat.
In Mexico, farmers have bred and preserved thousands of different traditional varieties of corn. Each variety is specific to location, micro-climate and soil type within that country. As such, Mexico is the world’s most important centre of biodiversity for corn, with 20,000 corn varieties and plant relatives, including the progenitor species of corn, called teosinte. With this much biodiversity, we have very high levels of resilience to factors that can endanger production of a staple food that a large portion of the world depends upon.
By growing many varieties of corn, if one variety succumbs to pests or disease, the resistant varieties survive. If this diversity is lost, it would place future food security at risk. One way for this biodiversity to be lost is through genetic contamination from GM (genetically modified) corn, which could overwhelm the indigenous varieties, and leave no other source of uncontaminated seed, and lead to the extinction of the local varieties. If a pest or disease were to strike, it may then affect all varieties, which would lead to massive global food shortages. Basically, world food security depends on the availability of this biodiversity.
We can apply this strategy with more than just staple foods. We can use it with any plants that come in different varieties, be it fruit trees or vegetables. Often, you’ll see different cultivars of a plant or tree, this just refers to a ‘cultivated variety’. By using various cultivars, we can ensure we still have a harvest when unexpected changes in seasonal weather take their toll. when pests or diseases strike (sometimes due to irregular seasonal weather) or simply when we wish to enjoy different flavours of natures bounty.
For example, different varieties of plants and trees can deal with sudden seasonal weather changes better than others.
A recent weather fluctuation here turned our dry temperate summer into a humid tropical one for a few weeks, totally destroying all early season stone fruit. Any varieties of stone fruit that produce late in the season escaped the calamity as the weather returned back to normal by the time their fruit was starting to grow.
Another seasonal fluctuation resulted in a very short. almost non-existent summer. Tomatoes need a good, long, hot summer, and for a change I planted a few varieties of smaller tomatoes (cherry tomato varieties) in addition to my main variety of large tomatoes that I plant each year. The short summer did not allow the large tomatoes to mature, so the harvest was greatly reduced, but luckily the cherry tomatoes flowered and fruited earlier than the main type I grow, and continued to produce when the other variety stopped.
It is quite clear that by using different varieties of plants and trees, we can ensure a continuation of the harvest, even when suffering losses of some of our produce. The key is biodiversity, that’s how nature ensures its survival and continued growth, and that’s the best mechanism for us to use, since our approach in Permaculture is to model nature’s ‘best practices’ in our designs!
Throughout human history, we have survived off seasonal produce, but using our ingenuity we have devised means of extending the use of the surplus harvest so it can sustain us through the less productive and less abundant seasons, such as through the cold winters.
We have learned to smooth out the lean times through preserving food – through a wide variety of techniques. Storage of grains and legumes, drying of fruit, using fruit and berries in jams and preserves, pickling of vegetables, fermentation of vegetables, and making alcoholic beverages from the fermentation of fruit juices, grains and even vegetables.
With this in mind, some varieties of produce lend themselves better to preserving than others. They either taste better, hold together better through the preserving process, or have a composition that favours preserving. For example, if you wanted to grow plums for drying, one of the best varieties would be prunes. Certain stone fruit varieties make for better preserves than others, so if you’re selecting peaches to bottle, select the varieties with the correct texture that are recommended for this purpose. Certain varieties of figs make tastier dried figs than others, as do certain apricots. So, where possible, if you wish to employ food preservation, plan at the outset to include varieties that are best suited to whichever preserving method you wish to employ. You’ll be glad you did when it comes to eating your preserved produce!
C. Function – Energy
The third important function that we need to pay attention to in our designs is Energy.
The input of energy is required in any system to create change, to move things from one state to another, to perform work. By employing a variety of energy sources, we once again have a back-up, a fail-safe, we eliminate any single point of failure, so our systems continue to run if any one of our energy sources were to be cut off.
Energy can be derived from:
- Non-renewable sources - such as fossil fuels (coal, oil, gas)
- Renewable sources – such as solar power, hydro systems, wind power, wood and other sources of biomass
Where possible, the logical preference is for renewable sources of energy, as they can be replenished on-site without having a dependency on outside sources.
- If the site design utilises non-renewable energy sources, such as bottled gas, petrol/diesel, grid-supplied electricity, these can be backed up and/or complemented by renewable energy sources.
- Renewable energy sources can also be used to back up up other renewable sources. For example, wind power generators can be used to generate additional electricity over winter when the output of solar cells is quite low.
- Non-renewable energy sources can be used to back up other non-renewables. A common example is a petrol driven generator that can supply power when the grid supplied power is disconnected or becomes unavailable.
The preference is to use renewable sources of energy in our designs because they are a sustainable energy source, and they allow us to create little to no pollution of the environment in the process, which is important in Permaculture systems.
Here is a brief overview of some of the renewable energy sources available to us that we can include in our designs:
Solar power in the home is provided through solar photovoltaic cells (solar panels) to generate electricity, or from solar thermal (solar hot water) systems to provide hot water.
Solar energy is a renewable source of energy that is inexhaustible and non-polluting, unlike fossil fuels which can and will run out, which are polluting and produce greenhouse gases when burnt.
In areas that have regular sunny weather, solar power is a viable source of alternative energy.
Solar Generated Electricity
Solar cells are referred to as photovoltaic calls (abbreviated PV) – photo means light, and voltaic implies that voltage (electrical power) is produced.
Solar generated electricity can be used to supplement mains supplied power, or it can be used to replace it completely.
It can be connected to the mains power grid, where it can be used in the home at the time it is being produced, and any time it’s not being used in the home, it feeds back into the mains power grid, supplementing the mains power supply. Many power companies will provides households with a credit on their power bills for generating electricity.
With this system, feeding power back into the grid during daylight hours, when the sun is shining, coincides with the period of highest power demands by industry and corporate offices.
The drawback with this arrangement is that there is no solar power available for the home at night, or when the sun is not shining. By connecting a bank of rechargeable batteries, the energy can be stored, and is available at any time. Adding batteries to a solar power system increases the cost, but extends functionality and versatility to a great extent. By having batteries to store solar power, households can go ‘off the grid’ – that is, generate all their own power and run without any connection to the mains power supply.
Solar power systems can be quite expensive to set up initially, and the initial outlay of money can be discouraging to many people, but the long term benefits of solar can be significant, and they pay for themselves after many years.
Solar Hot Water
Solar water heaters use either a flat plate with collector panels (dark painted metal plate with fins, similar to a car radiator, that provides a lot of surface area to heat up in the sun, and warm the water) or evacuated tubes (similar to a thermos, the vacuum means there is no air to carry the heat away, while the sunlight shines through the glass to bring heat in, and heat up the water). the result in either case is that the warmth of the sunlight raises the temperature of the water.
Solar hot water heaters can be used in conjunction with gas hot water heaters, where they can pre-warm the water in colder months, and completely heat the water without using any gas in the warmer months.
Solar water heaters can reduce our dependency on fossil fuels, and save a lot of money on water heating. One third of all greenhouse gases produced by households come from water heating, so there is a significant environmental benefit too.
In Melbourne, Australia, where the climate is classed as Cold/Temperate, a solar hot water system can supply free hot water for around two thirds of the year. In warmer climates, hot water is available for even longer periods.
Solar power can also be used for solar pumping water to an elevated tank. This coverts the solar energy to what is termed in physics as ‘potential energy’.
The potential energy here is the energy stored in the water due to its position in respect to gravity.
Since the water at an elevated height has the potential to perform ‘work’, it can be used for gravity-fed irrigation without pump, or it can be run through a mini-hydro system to generate electricity.
One important fact to keep in mind is that no energy generating system is 100% efficient, so whenever you convert energy from one form to another, you lose energy in the process. For example, the highest level of efficiency in converting sunlight into electricity with a solar panel is around 21%. A pump is driven by an electric motor. An electric motor converts electrical energy into mechanical energy, and is roughly 90% efficient (some energy is lost to mechanical friction and electrical losses). A mini-hydro is a pump working in reverse, you push water through it to generate electricity. You lose energy each time you convert from one form to another. Going from a pump to a mini-hydro, both which are around 90% efficient means you only end up with 0.9 x 0.9 = 0.81, or 81% of the energy you started with. If we include the solar panel, it’s 0.21 x 0.9 x 0.9 =0.17, in other words only 17% of the original sunlight gets captured. So remember, the fewer steps in energy conversion from one form to another, the more efficiency, and the least energy is lost.
Wind power is generated using wind turbines, which convert wind into electricity.
Wind is caused by differences in air pressure or changes in atmospheric temperature. Where there are difference is air pressure, air moves from areas of higher pressure to areas of lower pressure. Warm air rises and cooler air sinks toward the ground. The energy inherent in the movement of air can be used to spin a wind turbine, which drives a simple electrical generator, to generate electricity.
Since wind is a natural atmospheric phenomenon, wind power is a clean energy source of renewable energy. One wind turbine can be sufficient to generate enough electrical energy for a household.
Wind is only a viable source of energy in areas that have fairly constant windy conditions, and since the wind does not blow constantly in the same way the sun shines during the day. wind is not a consistent energy source, so it is often used to supplement other energy systems rather than function as a complete stand-alone system.
Micro Hydro Systems
Micro hydro systems convert the flow of water into electricity.
Flowing water from a small stream is used to rotate turbine blades which drive an electrical generator, to generate electricity . The power output of a micro-hydro systems depends on the amount of water flowing, as well as the size of the turbine itself.
Micro-hydro systems are efficient energy sources, as it only takes a small flow of water to generate electricity. They are also very consistent and reliable source of energy as a stream flows constantly, all day and night. Since micro hydro systems are continuously running, and therefore continuously generating power, they can be used as a stand alone power system. This allows the household to be disconnected from mains grid power, and run ‘off the grid’. As such, micro hydro systems are ideal for remote areas with continuously flowing water.
Micro-hydro is quite inexpensive, and affordable for a small home.
There are a few limitations to be aware of with micro-hydro systems. Most obviously is the requirement for a stream or other source of flowing water. Since output is dependent on water flow, seasonally fluctuations in water flow will affect the how much electricity the system generates. In winter, with lots of rain, streams flow faster, but during the summer, where there might be less rain, the flow of the stream will be slower, and less power will be generated. By supplementing the micro-hydro system with solar power, this possible reduction of power output in summer in a micro-hydro system can be overcome by taking advantage of the high sunlight levels, which is where solar cells run at their best.
The only other consideration that needs to be raised with micro-hydro systems is the possibility of negative environmental impact on the stream that will be utilised for this purpose. By performing a thorough evaluation of the stream where a micro-hydro system will be set up, the best site can be chosen so as to avoid any adverse effect on the environment.
Geothermal energy generation involves drilling deep into the ground to gain access to the heat that arises deep within the planet to either generate electricity or as a source of direct heating.
This is a rather specialised energy system that is limited to specific areas, and is not easily set up by an individual. These systems release greenhouse gases from deep within the earth (though less than fossil fuel burning power generation plants), and the dissolved gases and hot water from geothermal sources may carry trace amounts of toxic chemicals such as mercury and arsenic. There is also the possibility that groundwater contamination with geothermal systems. Furthermore, there is the issue of local depletion, which necessitates the drilling of more bores when the power output begins to fall off in the long term.
Since the process of drawing heat from deep within the earth is rather intrusive, can lead to local depletion (and is therefore not truly renewable), is not truly clean and is not a system that can be set up readily, it is only included here for the sake of completeness, and does not represent an energy source that is of equal viability to the previously mentioned systems such as solar, wind and hydro.
Keeping things in perspective, while there are still many other systems that have been proposed to generate power, such as tidal systems that use the rise and fall of the ocean tides to generate power, these, like geothermal, are in a class that I term ‘inaccessible’, it’s not like you’ll be setting up a geothermal system or a tidal power generator in any of your permaculture site designs for a while yet…
D. Function – Fire Protection
The fourth important function that we need to pay attention to in our designs is Fire Protection.
Wildfires are fire that burn uncontrollably in a natural settings (wilderness or rural areas), consuming combustible vegetative fuels, such as forests or grasslands.They are also referred to as bushfires, forest fires, grass fires, depending on the location where the fire occurs.
Fire protection as a function is particularly relevant to rural properties, especially in Australia, the driest continent in the world, which is plagued by periodic bushfires.
Because of the widespread destruction caused by fire, the name of the game here is risk minimization. With the other important functions discussed earlier (water, food and energy) the aim is to preserve and maintain the continuity of these functions. With wildfire, the aim is prevention and reduction of damage.
NOTE: This section is not intended to be a comprehensive instructional how-to guide on fire protection, it is only meant to be a discussion of the key principle, along with examples of the practical applications of the principle. For a more thorough coverage of the topic, I recommend David Holmgren’s book – The Flywire House: A Case Study in Design against Bushfire and Permaculture, a Designers’ Manual (section 12.16 – Wildfire) by Bill Mollison. I have used these two sources as reference for this section.
Let us now look at the various approaches to the function of Fire Protection that need to be incorporated into a design.
The spread of a wildfire can be reduced, and the intensity decreased, by the use of firebreaks. These are areas that are not very combustible, have little or no fuel to feed the fire, are fire retardant, or have been intentionally cleared or constructed to prevent the spread of fire. Also, if glowing embers or small pieces of burning material are blown into these areas, they are extinguished due to lack of fuel or high moisture levels, the fire cannot re-ignite itself and continue on.
Effective firebreaks include:
- concreted areas
- cleared ground
- stony ground
- summer-green or sappy plants
The wider these firebreak areas are, the better. It is important to keep in mind though that wind and updraughts created by the heat of the fire can carry burning materials for considerable distances and easily over a very wide firebreak.
The area surrounding the house is usually cleared to a distance of 30-50m (100-150’) of any loose fuels or flammable materials to create a firebreak.
The area past the cleared space around the house can be planted with a barrier of fire resistant trees and plants, to create a shelter belt, as discussed below.
A shelter belt is a wide strip of deciduous fire resistant trees and plants that can shield the house from radiant heat, and catch wind blown burning embers.
Trees suitable for this purpose are typically European deciduous trees, such as deciduous fruit and shade trees.
A selection of suitable trees includes:
- Deciduous fruit trees in general
- Poplars, aspens, and cottonwoods
- Coprosma repens (mirror bush)
I have included an extensive list of fire retardant and resistant plants and trees for reference purposes below. A shelter belt can be planted at the boundary of the 30m perimeter between the house and the surrounding forest or wilderness.
Below is a table which summarizes the properties of plants that are fire resistant and those that are not:
Fire Resistant Plants
The following types of plants are less likely to catch alight and burn in a bushfire:
Plants which are more likely to burn include:
Source : ACS Distance Education – Webphotos Free Articles, Designing a Fire Break
This is an extensive list of plants and trees that can be used in the design of a shelter belt:
Fire Retardant Flora
There are many varieties of trees, shrubs and ground covers which resist intense burning and/or have less chance of contributing to ember attacks. These plants have a number of distinguishable features, including a high salt and moisture content and a low volatile oil content in the leaves.
Usually fire retardant trees have thick, well-defined bark and few branches which grow low to the ground. These trees and shrubs rarely shed large quantities of leaves and twigs and their seeds are usually enclosed in woody capsules.
It should be noted that under the right circumstances, such as a fire’s intensity, that even fire retardant plants can and will burn. It is the degree of resistance and their ability to reduce airborne embers that make fire retardant plants attractive. Used in conjunction with other landscaping techniques (e.g. rocky outcrops) they can be an effective method of slowing and reducing the intensity of an approaching fire front.
Australian Trees that are fire retardant
Non-Australian Trees that are fire retardant
Shrubs that are hard to burn
Ground Covers that are hard to burn
Source: Publication of the Glen Forrest V.B.F.B, adapted from “Trees and Plants for Bush Fire Prone Areas,” Fire and Emergency Services Authority Australia, 2002.
The location of buildings is the fist step in common sense fire-protection design. By understanding which locations are most vulnerable to fires, we can avoid these areas and site buildings in locations that afford the greatest degree of fire protection.
The mistake commonly made by people not knowing any better is to site locate a building in the worst possible place, and then try to implement fire protection measures, or design away the problem. This simply can’t be done.
A common example of this occurs In Australia, people sometimes have the misguided idea they want to build a house ‘surrounded by native forest’ often with only one path in… Since 75% of our forests here are Eucalyptus forests, that’s what they most likely surround themselves with. They cut a single path into the centre of a forest patch, and clear a spot to build a house. Eucalypts are flammable as drums of petrol/gasoline pilled up metres high, and such a location is a death trap. No amount of designing will correct such a grave error. Put simply, it’s suicide…
In areas where the ground is not flat, and the house is located on a slope, the biggest danger is from fires running from the downhill area up the slope. These are called upslope fires.
The steeper the slope. the higher the risk. The speed and intensity of the fires doubles for every 10 degree increase in the slope angle. This is happens for two reasons:
- The angle of the slope allows the fire to dry the material uphill, making it more flammable when the fire reaches it, and
- The updraught effect – when a fire burns, the heat creates an ‘updraught’, hot air rises fast, and the fire pulls in more oxygen-rich air from lower downhill to feed it. The more air that feeds in, the hotter it gets, and the fiercer it burns.
As a consequence, the worst places to site a house is on sharp rigdetops or hilltops. The house is exposed from all sides to the threat of fire, and fire will race quickly up the slope to reach the house.
Another risky spot is the lee side of a hill, that is, the side of the hill sheltered from the wind. As the wind blows over the crest or top of the hill, it creates a low pressure area on the lee side, which creates a lot of air movement. Dusring a fire, this powerful air movement can drive a fire cyclone, which will be burning directly over the house!
To reduce the risk of fire, houses need to be sited:
- Away from the tops of hills or ridges
- Preferably on downslope plateaus (level areas)
- If the house is located on a slope of a hillside, excavate a shelf, a flat area, and locate the house on the shelf, well back from the edge to protect it from radiant heat coming from the downhill area.
- If excavating a shelf, build a pond as a firebreak or an earthbank to protect the house from radiant heat.
Fires continue to burn as long as fuel to burn is present, so it is important to remove:
- Any flammable materials around the house that can be ignited by glowing embers blown by the wind, or that can carry the fire closer to the house.
- Any flammable materials on the property that can increase the intensity of a passing fire.
Fuel Reduction Around the House
To prevent any burning embers blown by the wind from starting a fire near the house, or setting the house itself on fire, it is important to clear the space 30m (100’) wide or more right around the house.
This means removing any loose flammable material such as dry sticks and branches, dry grasses, firewood piles and so on. Anything organic with a low moisture content, if it is not overly large, will burn.
Trees and plants do not have to be removed from this area, as long as they are not a fire hazard. Deciduous trees, including deciduous fruit trees, sappy and moisture rich plants, and ground cover plants that are green in summer all help to reduce the danger or radiated heat, the dense growth creates a shield to catch burning ember, and they burn very slowly or not very well and reduce the intensity of the fire.
Trees that are high in resins and volatile oils, such as eucalypts and pine trees, are a major fire hazard and should be cleared from around the house perimeter. These burn intensely as they are high in hydrocarbons, the same class of chemical compounds as petrol/gasoline and other highly flammable solvents and fuels. If you have these close to your youse, it’s akin to stacking filled fuel drums around the house, and just as safe.
Fuel Reduction Around the Property
The severity of a fire can be reduced if materials that can fuel a fire are removed periodically.
Tall grasses and plants, which dry in summer and create an ideal tinder which can start a fire, can be controlled by:
- Allowing livestock to graze in the area in spring/summer
- Slashing or mowing and using as mulch or compost
Dry braches and twigs need to also be removes, these serve as kindling if a fire gets started, can be:
- gather and stored away for use as kindling and firewood, which will be burnt during winter for heating/cooking
Fallen leaves are also another fire hazard when dry, wit these:
- Rake all fallen leaves that do not easily decompose by winter away, gather and compost
- Remove all leaves from gutters, fit leaf guards to stop gutters collecting leaves
To prevent fires reaching into the crowns of the trees (a crown fire is unstoppable!)
- Remove lower branches – prune trees
- Remove any dead or dry branches – prune trees
- Collect any fallen branches or twigs under trees
- Plant fire-retardant ground cover plants under trees
To better survive a fire,rural houses and other building structures are often fitted with sprinkler systems on the roof and micro-spray type systems attached under gutters around the eaves to put up sparks/embers around the house. Hoses are used to extinguish any spot fires or dampen down areas.
These are suppled by water systems that have built in redundancy in terms of power and supply. Since mains power may be often cut off in a fire, water can be gravity fed, or pumped via an independent solar charged battery driven system. The water can be supplied via gravity from a rooftop/elevated tank or pumped via tanks or a high capacity dam.
It is important that these systems are designed to resist heat/fire and function for as long as possible in the event of a fire.
A detailed discussion of these water systems is beyond the scope of this short section, the point is that this aspect of fire safety needs to be incorporated into the design, and a lot of though needs to be put into how it will operate, and how it will continue to run in the event that one system should fail.
In summary, the success of a fire protection systems does not depend on any one single element, but on the many elements of which it is comprised working together to create a comprehensive functional system. From building location and earthworks, to tree and plant selection, through to water supply systems, each part plays a role in building a complete fire protection system.
As an overall summary, we have now seen how each important function in a design, Water, Food, Energy and Fire Protection, is supported by many elements to create a fault tolerant, resilient system which ensures the continuing functionality of our system, even in the most adverse circumstances.
Utilising this third design principle, we can design resilient systems that minimise the chance of a disaster brought about by the failure of any one of the critical functions.
After all, in Permaculture we model our systems of those of nature, and Nature only builds resilient systems!