Landscaping for bushfire garden design and plant selection



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EXISTING HOUSES


The information outlined above about defendable space and landscaping is relevant to planning a garden for existing houses.

However, there are also some specific points that need consideration.


CONSTRUCTION


The resilience of existing houses can be improved by retrofitting some building elements.

More advice can be obtained from A guide to retrofit your home for better protection from a bushfire (see Further Resources).


PROVISION OF SERVICES


In high bushfire risk areas, it is recommended that a dedicated water supply is installed for firefighting purposes. Where possible, access should meet the requirements as outlined for new houses.

RULES FOR VEGETATION CLEARANCE AROUND EXISTING HOUSES


Throughout Victoria there are restrictions for vegetation clearance on private property. These are contained in the planning scheme of each municipality. In many cases, a planning permit is required to remove vegetation.

In areas where bushfire is a risk, there are particular circumstances where a permit is not required for vegetation removal around existing houses.

For example, the Victoria Planning Provisions Clause 52.17 Native Vegetation outline exemptions that apply for removing, destroying or lopping native vegetation for fire protection. Clause 52.48 Bushfire Protection: Exemptions refers to the 10/30 and 10/50 rules.

To find out if these exemptions apply to a particular council, refer to the relevant planning scheme (see Further Resources).


THE 10/30 RULE


The 10/30 rule applies to a building used for accommodation that was:

  • constructed before 10 September 2009 or approved by a planning or building permit issued before 10 September 2009.

It allows landowners to:

  • Remove, destroy or lop any vegetation within 10 metres of an existing building used for accommodation.

  • Remove, destroy or lop any vegetation, except for trees within 30 metres of an existing building used for accommodation.

  • Remove, destroy or lop any vegetation for a combined maximum width of 4 metres either side of an existing fence on a boundary. The fence must be between properties of different ownership and have been constructed before 10 September 2009.

THE 10/50 RULE


The 10/50 rule applies only to land in the Bushfire Management Overlay. It applies to a building used for accommodation that was:

  • constructed before 10 September 2009 or lawfully erected before 18 November 2011 without the need for a planning permit

  • approved by a planning or building permit before 10 September 2009 and erected before 18 November 2011

  • approved by a building permit before 10 September 2009 and erected before 18 November 2011.

The 10/50 rule allows landowners to:

  • Remove, destroy or lop any vegetation within 10 metres of an existing building used for accommodation.

  • Remove, destroy or lop any vegetation, except trees, within 50 metres of an existing building used for accommodation.

  • Remove, destroy or lop any vegetation for a combined maximum width of 4 metres either side of an existing fence on a boundary between properties. The fence must be between properties of different ownership and have been constructed before 10 September 2009.

Important


In high bushfire risk areas properties may need a greater amount of defendable space. Clearance over the distances stipulated in the 10/30 and 10/50 rules require a planning permit.

SECTION 4: DESIGNING A GARDEN


Effective defendable space, house construction, water and access in new and existing gardens can all be compromised by inappropriate landscaping.

The location, type and ongoing maintenance of vegetation within a property have a significant impact on the bushfire risk to any house. These factors can prevent the accumulation of debris and prevent the spread of fire towards a building.

When designing a new or modifying an existing garden carefully consider the placement of garden beds, trees and other vegetation to reduce the bushfire risk to the house.

When selected and located correctly, plants can filter embers, absorb radiant heat and break up fuel in the path of a bushfire.

However, plants can also contribute to house loss by:


  • providing a continual fuel path to the house, allowing direct flame contact

  • dropping leaf litter on the ground, which readily ignites and can become embers

  • dropping limbs or tree branches onto the house

  • adding to fuel loads on or near the house, such as creepers over pergolas, fences or verandahs

  • if located too close, can produce radiant heat that may ignite the house or cause windows to break, allowing embers into the house

  • acting as ladder fuel from the ground into tree canopies, increasing the intensity of the fire.

Vegetation should always be kept clear of access to and from the house and property.

DESIGN PRINCIPLES


The following design principles outline how defendable space can be used to reduce radiant heat, prevent flame contact and minimise ember attack on the building.

These design principles are based on the bushfire protection requirements within the Bushfire Management Overlay.

These principles should be followed in all types of gardens.

DESIGN PRINCIPLE 1: CREATE DEFENDABLE SPACE

WHAT IS IT?


Defendable space is an area of land around a building where vegetation is modified and managed to reduce the effects of direct flame contact and radiant heat associated with bushfire. It breaks up continuity and reduces the amount of fuel available to a bushfire.

Managing vegetation within the defendable space does not mean clearing all plants and trees. There may be opportunities to retain existing vegetation depending on its flammability, location and management.

Whether starting from scratch or making changes to an existing garden, there are ways to design an effective defendable space.

Defendable space needs careful garden design and regular maintenance. It consists of an inner and an outer zone:



  • The inner zone is the area immediately around the house. It provides separation from fuel sources, reduces radiant heat, eliminates direct flame contact and reduces ember attack. Vegetation needs significant and intensive management. Fuel is managed to a minimum level in this zone.

  • The outer zone sits between the inner zone and unmanaged vegetation (beyond the defendable space). Vegetation is managed to a more moderate level to substantially decrease the ground fuel and restrict the fuels available to an approaching bushfire.

HOW TO CALCULATE IT


Requirements for defendable space will vary. They depend on the type of development and the level of bushfire risk to the property.

New houses in a Bushfire Management Overlay


As part of the planning permit process, defendable space requirements are determined by a bushfire site assessment. Permit conditions will prescribe the inner and outer zone distances for vegetation management. The site assessment process is outlined in DPCD Practice Note: 65: Bushfire Management Overlay and Bushfire Protection: Planning Requirements (see Further Resources).

In the inner zone fuel should be managed to the following condition:



  • Within 10 metres of a building, flammable objects such as plants, mulches and fences must not be located close to vulnerable parts of the building such as windows, decks and eaves.

  • Trees must not overhang the roofline of the building, touch walls or other elements of a building.

  • Grass should be no more than 5 centimetres in height. All leaves and vegetation debris are to be removed at regular intervals.

  • Shrubs should not be planted under trees.

  • Plants greater than 10 centimetres in height at maturity must not be placed directly in front of a window or other glass feature.

  • Tree canopy separation of 2 metres and overall canopy cover no more than 15 per cent at maturity.

The outer zone fuel should be managed in the following condition:

  • Grass must be no more than 10 centimetres in height and leaf and other debris mowed, slashed or mulched.

  • Shrubs and trees should not form a continuous canopy.

  • Tree branches below 2 metres from ground level should be removed.

  • Trees may touch each other with an overall canopy cover of no more than 30 per cent at maturity, with few shrubs in the understorey.

  • Shrubs should be in clumps no greater than 10 square metres, which are separated from each other by at least 10 metres.

For both the inner zone and outer zone:

  • Non-flammable features such as tennis courts, swimming pools, dams, patios, driveways or paths should be incorporated into the proposal, especially on the northern and western sides of the proposed building.

  • Features with high flammability, such as doormats and firewood stacks, should not be located near the structure.

Existing houses and houses outside the Bushfire Management Overlay


Defendable space can be calculated using CFA’s online Household Bushfire Self Assessment Tool available at cfa.vic.gov.au. Ideal defendable space requirements can be worked out using this tool.

WHAT TO INCLUDE


Plants and other flammable objects provide fuel for bushfires and defendable space requires ongoing maintenance.

When modifying an established garden, it is critical to consider existing vegetation and other flammable objects within the defendable space.

If planting new vegetation, ensure that it is not compromising the effectiveness of the defendable space by significantly increasing the amount of fuel or adding to its continuity.

Landscaping for bushfire should:



  • Locate areas of low fuel between the house and the bushfire hazard (for example, maintained lawn, ponds, pools and tennis courts).

  • Locate farm machinery, sheds and poison well away from the house (as they too may become fuel in a bushfire).

  • Use landscaping features to provide barriers to wind, radiant heat and embers (such as stone walls and non-combustible fences).

  • Use materials such as brick, earth, stone, concrete and galvanised iron. These can act as radiant heat barriers.

  • Use driveways and paths to create separation between vegetation and the house. Suitable materials include clay, concrete, gravel and pebbles.

  • Locate non-combustible water tanks to act as radiant heat barriers.

DESIGN PRINCIPLE 2: REMOVE FLAMMABLE OBJECTS FROM AROUND THE HOUSE


The area immediately surrounding a house should be clear of flammable objects that can catch fire during a bushfire.

Within 10 metres of a building, flammable garden materials (such as plants, mulches and fences) must not be located close to vulnerable parts of the building (such as windows, doors, decks, pergolas and eaves). The intention is to prevent flame contact on the house.

There are a number of things that can be done to support this design principle:


  • Locate non-flammable surfaces (such as paths, driveways and paved areas) against the house.

  • Ensure trees are planted away from the house so they do not cause damage if they fall. They must not overhang the house and should be located 1.5 times their mature height from the house.

  • For example, if a mature tree height is 8 metres, it should be planted at a minimum of 8 metres x 1.5 = 12 metres away.

  • Maintain grass to no more than 5 centimetres in height in the inner zone and 10 centimetres in the outer zone.

  • Use non-combustible, moveable containers and pots that can be relocated in the summer.

  • Avoid flammable mulches within the defendable space. Mulch is used to improve the quality of soil, improve water efficiency and keep plants cool and moist in the summer. Most mulch used in gardens can also be a bushfire hazard as it will dry out and burn.

  • Alternatives include gravel, scoria, pebbles, shells or recycled crushed bricks. These materials provide the same role and come in a variety of shapes and colours.

  • Remove other flammable objects from around the house. These include sheds, caravans, outdoor furniture, barbeques, gas bottles, wood piles and organic mulch.

These should not be placed within 10 metres of the house and must have adequate separation from other flammable objects, including plants.

DESIGN PRINCIPLE 3: BREAK UP FUEL CONTINUITY


One of the most effective ways to reduce the spread of fire within a garden is to create separation between plants, garden beds and tree canopies.

Fire spreads easily when plants are located close together.

When a plant catches fire it can preheat and ignite the vegetation around it through radiant heat or direct flame contact.

If there is continuous vegetation leading up to and surrounding a house, fire is likely to spread throughout the garden to the house. Grouping plants and garden beds with areas of low fuel between them can help avoid this by breaking up fuel continuity.

Ways to reduce fuel continuity include:


  • Locating shrubs or other flammable objects away from trees. If planted under trees, vegetation can act as a ladder fuel and carry fire into canopies.

  • Clumping shrubs and trees so they do not form a continuous canopy and are separated by areas of low fuel.

  • Using gravel paths, non-flammable mulch and mown grass to provide separation and areas of low fuel between plant groupings and garden beds.

  • Pruning branches to a minimum of 2 metres above the ground. This increases the vertical separation between fuel at ground level and the canopy.

DESIGN PRINCIPLE 4: CAREFULLY SELECT, LOCATE AND MAINTAIN TREES


Trees can be useful during a bushfire, provided they are:

  • selected carefully

  • properly maintained

  • located at a safe distance from the house.

Bushfires are often accompanied by strong winds, which may cause branches to break or whole trees to blow over. Trees can also catch fire, burn through and fall over.

Correctly selected and located trees can:



  • reduce wind speed

  • absorb radiant heat

  • filter embers.

Fire is rarely sustained in the tree canopy, unless there is a fire burning in the plants or leaf litter under the tree.

When implementing this design principle:



  • Avoid trees with loose, stringy or ribbon bark.

  • Separate tree canopies by at least 2 metres.

  • Canopies should cover less than 15 per cent of the inner zone and 30 per cent of the outer zone.

  • Prune branches to a minimum of 2 metres above the ground increasing the vertical separation between fuel at ground level and the canopy.

  • Locate trees at a safe distance from all other buildings, driveways, water supplies and powerlines. They should be at least 1.5 times their mature height away.

  • Do not plant trees near shrubs, as shrubs can carry fire into tree canopies.

  • Periodically remove dead leaves, bark and branches as well as leaf litter from underneath trees around the house.

Windbreaks


Trees can also be planted for windbreaks but are most effective in a fire of low to moderate intensity.

However, windbreaks are only one of many factors that affect the speed and progression of a bushfire.

Windbreaks are not a stand alone solution because:


  • it takes time for trees to grow and they may not provide protection for some years

  • wind direction can change and spot fires occur, allowing bushfires to approach from any direction.

Other things to remember are that:

  • there needs to be adequate separation between a building and the windbreak

  • a windbreak should not be planted within the defendable space

  • trees should be carefully selected and will require ongoing maintenance

  • highly flammable trees will become a fire hazard

  • the windbreak should be planted at right angles to prevailing winds

  • the windbreak should allow some wind to pass through

  • the windbreak should have a continuous length of at least 100 metres if possible

  • slashed, well-watered grass should be planted underneath the windbreak

  • routine maintenance must be carried out to remove leaf litter and other dead plant material from underneath the windbreak.

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