Biology Reference
In-Depth Information
completely blocked of will determine by what
degree the airfl ow is reduced. Whilst in principle
woven material typically used for protecting
vegetables from UV exposure - such as
polyethylene 'Maxixe' cloth and durable linings
such as ZeroVector® - could be adopted for
house screening, airfl ow would be reduced by
up to 95%, and ultimately may be rejected on
these grounds (Kampango et al ., 2012). A fi nal
but not insignifi cant consideration in relation to
thermal comfort is the possibility that house
screening would reduce the use of bed nets.
There is limited evidence of reduced net use in
screened houses (Kirby et al ., 2010), but it is
unclear if this reduction was driven by the
decline in mosquito numbers or by a rise in
night time temperatures to an uncomfortable
level. Careful studies of indoor environmental
conditions are needed where both intervention
tools are deployed.
Although perhaps not as critical as issues
of ei cacy, cost, durability and ventilation, it is
important to realize that eave gaps and windows
provide illumination (Kampango et al ., 2012).
Against this, one must also consider the ethno-
geographic variation in the importance of the
house during daylight hours. In many cultures
the house is unoccupied for most of the day, or
serves as a resting place for only a few of the
daylight hours. In such situations restricted
indoor illumination may be of no concern or
even benefi cial.
Housing, of course, is much more than a
controlled climatic environment. The social and
psychological needs met by housing will
probably outweigh marginal considerations of
physical comfort. In considering problems of
tropical housing, public health researchers and
architects from Westernized nations may put
too much emphasis on material comfort, and be
too quick to introduce technological improve-
ments. It is clear that housing solutions in
impoverished rural societies will not be able to
af ord climate controlling devices such as air
conditioning, double roofs or heat-absorbing
glass. Uncomfortable gain, storage and emission
of heat must therefore be kept within reasonable
limits by the application of simple climatic and
biological principles to planning and design, and
by the selection of construction materials based
on their thermal characteristics.
7.6 Perfecting the Vector-proof House
The development of a vector-proof house that is
durable and acceptable, yet cheap enough to
build and maintain, should be considered a
research priority for international agencies and
donors (Walker, 2010). House screening should
be incorporated into the construction of all new
houses and should be seen as much integral to
the building as a door or roof. This is because the
modifi cation of houses already built is dii cult
compared to selling a design plan that people
could buy with screening incorporated into that
design. Ideally, building materials familiar and
af ordable to end users should be adopted and
designs modifi ed in a sensitive, even conservative,
fashion in conjunction with those same people.
Such an approach was much more acceptable to
local populations in Venezuela, where house
improvement was attempted to control Chagas
disease, than the prefabricated building panels
that were originally deployed by the Ministry of
Health (Briceno-Leon, 1987).
Figure 7.4 presents a schematic of a vector-
proof house that could be built at very little
additional cost over current rural tropical house
designs. Houses should be oriented to minimize
exposure to solar radiation and maximize
ventilation by prevailing wind currents. Avoid-
ing a temperature rise indoors at night is
especially important, given that many vector
species are seeking a blood meal at that time and
high night-time temperatures may reduce the
use of bed nets and drive people to sleep outdoors.
Light coloured, low density construction
materials will refl ect heat energy and dissipate
any accumulated heat quickly, minimizing
night-time heat release. Materials must also be
cheap to transport and easily worked with simple
hand tools. Walls should be made of compressed
stabilized earth, kiln-fi red bricks incorporating a
bonding material, or a single thickness of timber.
Hollow walls should be avoided as these provide
breeding places for insects and vermin and
maintain moisture, which can accelerate
rotting. Appropriate roofi ng material is more
dii cult to defi ne. Traditional materials are
short-lived and fl ammable, but alternatives are
costly and unsuitable for tropical conditions.
Ideally the roof should absorb as little heat as
possible. Wood shingle roofs were once common
 
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