Thatch roofing: Innovations in
fire protection
The articles provided here are on an ‘as is’ basis and published for
you enjoyment only. In no event shall we be liable for any direct or
indirect damages or losses suffered with the use of these articles. |
|
|
‘How very little since things were made,
Things have altered in the building trade’
Rudyard Kipling
If one look at the quote above one can deduct that there has not
been a lot of innovations in the thatching industry, there has
however been huge advances in the fire protection of the
thatching material. Modern laying techniques also eliminate the
exaggerated fire risk that many people fear regarding thatch.
Nowadays various fire blankets are placed in between the thatch
and with the correct compaction the fire risk is virtually
eliminated and with the use of lightning conductors, thatch is
no longer the hazardous material of the past.
·
PREVENTATIVE MEASURES
Lightning protection
Lightning conductors should always be installed to protect the
thatched buildings. For single masts the angle of protection is
45°
from the highest point downwards and one should make sure that
the whole roof is covered by at least one meter above the roof
of the building. For a high risk zone of lightning for example
on sloping ground or on a hill, the angle of protection is only
30°
from the highest point downwards along the pole and naturally
the lightning conductor will have to be a lot taller or multiple
conductors can be installed. When more than one lightning
conductor is installed, the angle of protection between them is
60°
from their highest points downwards along the poles.
Binding
For lightning protection purposes, it is strongly recommended
that galvanized steel wire should not be used for binding the
thatch, and rather a suitable natural material should be used.
Poplar and wattle sticks are commonly used and some use cane or
thatch strands. Tar treated string should not be used for
binding as this can create a fuse-like effect in the event of
fire.
Chimneys
Chimney stacks should be constructed in such away that the
outer faces in contact with the thatch do not become hot. A full
brick thickness (220 mm) is normally sufficient to satisfy this
requirement. All mortar joints in the stack must be properly
filled. The top of the stack must extend to at least 1m above
the highest point of roof and a spark arrestor, (stainless steel
wire mesh), fitted close to the top, covering the full width of
the flue, must be built into the flue around the edges to
prevent sparks flying out and possibly ignite the roof.
Cabling & Services
Electrical power supply and telephone cables should enter the
building by means of underground ducts, and all electrical
wiring in the roof space should be run in screwed metal conduit,
with all junction boxes properly sealed.
Refuse
Combustible material should not be allowed to accumulate near
the house. A number of thatched roofs have, in the past, been
set on fire as a result of the burning of garden refuse in the
vicinity.
Adjacent buildings
Sufficient space must be allowed between buildings to prevent
fire spreading to the thatched building from adjacent buildings
and vice versa. Some countries’ regulations calls for at least a
15m distance between the building and its plot boundary line.
·
REDUCTION OF COMBUSTIBILITY
Fire retardant chemicals
Many fire retardant chemicals are available these days that can
be applied to thatch by immersion or spraying, but as these
chemicals are generally water soluble they are, in time,
largely washed out by rain as they do not penetrate the
material but only form a surface coating.
A lot of exposure to the sun will also gradually evaporate the
chemicals and might leave the top layer unprotected.
Fire resistant blankets
A protective, noncombustible membrane can be laid under the
thatching grass to act as a blanket preventing the spread of
fire between the thatch layers. Materials that are generally
used for such a purpose is aluminium, building paper or glass
fibre. The disadvantage of such a measure in warm, humid or high
rainfall areas is that because of the impervious membrane or
blanket, air flow between the thatch is restricted and will
enhance the growth of destructive fungi. To allow air flow
through the thatch to avoid fungi growth the chosen membrane
should be sufficiently perforated.
·
FIRE FIGHTING FACILITIES
Soaking with water
Perforated horizontal pipes can be provided on each side of and
running parallel to the ridge, controlled by stop taps at ground
level. The pipes can be of galvanized steel or copper,
perforated with holes at sufficient intervals along the length
of the pipe to discharge water over the roof surface in the
event of fire. Alternatively a horizontal pipe may be run inside
the roof at the ridge, with 'spreaders' protruding through the
thatch at sufficient intervals. Such installations can be used
to soak the thatch in the event of a fire risk. A high rate of
water discharge is needed for this to be effective and will not
be able to run of a domestic water supply. Special arrangement
will need to be made with the local council for such an
installation.
Other
There are two schools of thought about the value of swimming
pools as a source of water supply for fire fighting. Some local
authorities consider that a pool can be useful if located near
enough to the house and with unrestricted access for the fire
brigade.
However, some specialist organizations believe that thatch burns
so rapidly that the fire brigade can rarely reach the scene
before the fire has got a hold and that initial use of water
from the brigade's unit tanks would be quicker than using a
swimming pool supply.
A long-handled metal rake should be provided in an easily
accessible place, for pulling down smoldering thatch from the
roof. The handle may be fitted with a suitable clip to which the
nozzle of the hose pipe may be attached, thus improving the
reach of the jet.
Even when all these precautions have been taken, the occupant of
a thatched house must always exercise care when handling open
fires in or near the house e.g. when preparing for a bbq or
burning garden refuse or if fireworks are being discharged in
the vicinity.
Written by Jere Botes, architect & founder of
www.dreamhouses.co.za,
Reproductions of this article are encouraged but must include a
link pointing to http://www.dreamhouses.co.za
|
|
