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Introduction
Many
areas within Victoria are declared
Bush Fire Prone. Buildings constructed
in these areas will require specialised
components and methods to protect
the building against ember attack
during a Bush Fire. These measures
do not guarantee your building will
not burn, but do provide some protection
against attack provided an ongoing
maintenance and inspection regime
is also undertaken.
The
Building Code of Australia Part
3.7 and AS 3959 1996 provide details
of the specialised building methods
and components needed to construct
a building in a Bush Fire Prone Area.
The
methods and components are designed
to reduce a buildings susceptibility
to ember attack during a Bush Fire,
they do not provide protection from
a Fire Front.
The
Australian Standard AS 3959 1996 sets
4 categories for ember attack, the
Category specific to your property
can be identified by a site evaluation
in accordance with the method set
out in the Standard. A site evaluation
can be carried out by the CFA, your
Builder or your Building Surveyor
or an Accredited Bushfire Consultant.
-
Low, (no protection is required
in this category)
- Medium
- High
- Extreme
Parts
of the building that will require
special treatment are:
- Flooring systems.
- Supporting Posts, Columns,
Piers and Poles.
- External Walls.
- Windows.
- External Doors.
- Vents and Weep Holes.
- Roof Covering, Eaves and
Fascias.
- Roof Lights.
- Roof Ventilators.
- Roof Mounted Evaporative
Cooling Units.
- Gutters and Down pipes.
- Service Pipes (water and
gas).
- Verandahs and Decks.
FLOORS
(Medium / High Catagory)
Proposed flooring
systems can be one or any combination
of the following:
i) Concrete slab on ground;
ii) A suspended floor which can be
a concrete slab supported by complying
posts, columns, stumps, piers, poles
or walls;
iii) a suspended timber floor where
the underside of any one bearer is
not more than 600 mm above finished
ground level and which has flooring,
bearers and joists which have been
treated with a suitable fire retardant;
iv) a suspended timber floor where
the underside of any one bearer is
not more than 600 mm above finished
ground level and which has the ground/floor
gap enclosed by a wall which complies
with the requirements under WALLS.
Note:
Adequate sub floor ventilation is
essential.
SUPPORT
POSTS OR COLUMNS
Supporting posts
or columns can be one or any combination
of the following:
i) Non-combustible;
ii) Timber treated with a suitable
fire retardant for a minimum 400 mm
above finished ground level;
iii) Timber mounted on galvanized
metal shoes with a minimum clearance
of 75 mm from the finished ground
level or paving level (see diagram
2).SERVICE PIPES (e.g. water and gas)
Pipes shall be buried to a depth of
at least 300 mm unless they are metal.
All exposed piping is to be metal.
WALLS
The external walls
shall be one or any combination of
the following;
i) A wall where the external leaf
is masonry, concrete, pise, rammed
or stabalised earth, or;
ii) Where the cladding is other than
that specified above, a framed wall
that incorporated either an insulation
material confirming to the appropriate
Australian Standard or a breather
type sarking complying with AS/NZ
4200.1 and with a maximum flammability
index of not more than 5 (AS.1530.2)
installed directly behind the external
cladding.
Where
the external leaf or cladding is of
a combustible sheet material, it shall
be protected for not less than 400
mm above the finished ground level
by covering or replacing with suitable
non-combustible material or fire retardant
treated timber; or
Where the external cladding is timber,
either by covering or replacing with
non-combustible materials as above,
or by treating the section of cladding
with suitable fire retardant treatment.
(See diagrams 3 & 4 for wall protection
where combustible wall cladding is
used with a concrete slab.
ROOFS
- The following
requirements apply to all types of
roofs.
- No timber shakes or shingles
are permitted.
- Sarking shall have a maximum
flammability index of 5 (see AS 1530.2).
- The roof/wall junction shall
be sealed with fascias and eaves lining,
or by sealing the gaps between the
rafters with a suitable non-combustible
material.
- Acceptable roof tiles and
shingles shall be installed with sarking
located immediately below the tiling
battens and covering the whole roof
area including the ridge.
- For sheeted roofs, only metal
or fibre cements sheets may be used.
- Gutters shall be fitted with
devices to stop leaves collecting.
- Ridge capping shall be sealed
as above, or by suing pre-formed rib
caps where suitable (see diagram 5).
EAVES
All eaves shall
be enclosed, and the fascia or the
gaps between the rafters shall be
sealed.
GUTTERS
AND DOWN PIPES
All materials or
devise used to stop leaves collecting
in the gutters of construction shall
have a flammability index of not greater
than 5 when tested in accordance with
AS 1530.2.
ROOF
PENETRATIONS AND ROOF LIGHTS
All penetrations
of the roof for light shafts, vent
pipes and the like are to be sealed
with a non-combustible sleeve or lining.
Vented
roof lights shall be provided with
corrosion resistant steel or bronze
mesh having a maximum aperture size
of 1.8 metres.
ROOF
VENTILATORS
All components of
roof ventilators, including the rotary
type, shall be constructed of non-combustible
material and shall be sealed against
the entry of sparks and embers with
corrosion resistant steel or bronze
mesh having a maximum aperture size
of 1.8 mm.
ROOF
MOUNTED EVAPORATIVE COOLING UNITS
Roof
mounted evaporative cooling units
shall only be used if the openings
to the cooling unit are encased in
corrosion resistant steel or bronze
mesh with a maximum aperture size
of 1.8 mm.
WINDOWS,
DOORS,
VENTS & WEEP HOLES
All
windows, doors, vents and weep holes
shall be protected as follows:
WINDOWS
All openings sashes
and louvers shall be screened with
corrosion resistant steel, bronze
or aluminum mesh with a maximum aperture
size of 1.8 mm in such a way that
the opening remains screened when
the sash or louver is open.
DOORS
Exterior doors shall
be fitted with corrosion-resistant
steel, bronze or aluminum mesh screens
with a maximum aperture size of 1.8
mm and weather strips to prevent penetrations
or build up of a burning debris beneath
the door (door seals).
VENTS
AND WEEP HOLES
Vents and weep holes
shall be screened with corrosion resistant
steel, bronze or aluminum mesh with
a maximum aperture of 1.8 mm (see
diagram 6).
VERANDAHS
& DECKS
- A reinforced concrete suspended
slab floor, supported by complying
posts or columns or complying walls
or a complying slab-on-the-ground
floor is considered acceptable.
- Solid decking may be either
sheeted with particleboard, plywood,
compressed fibre cement or the like,
or tongued and grooved flooring timbers.
- Solid decking shall comply
with the abovementioned requirements
for floors. Also, where clearance
to the underside of the floor levels
400 mm or less above finished ground
level, all joints in the decking shall
be covered or sealed. Compressed fibre
cement sheet shall have a minimum
thickness of 15 mm.
Note: Flooring bearers and joists
may be required to be treated with
a suitable fire retardant, refer to
section on flooring.
- Open decking flooring timbers
shall be fixed with 5 mm minimum clearance
between adjacent timbers.
- The external perimeter ground/floor
gaps is not be sealed, in order to
provide access to extinguish burning
debris or fires.
- The base of any supports
are to comply with the abovementioned
requirements for supporting posts
or columns.
- Decking timbers shall not
be allowed to connect with the remainder
of the building unless measures are
used to prevent the spread of fire
into the building.
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