VERNACULAR ARCHITECTURE IN FLOOD PRONE AREAS (BANGLADESH)

INTRODUCTION:
-A large proportion of the countryside as well as the majority of urban areas in
Bangladesh is flood-prone. During heavy flood, more than 60% of the land is
inundated.
-Recent floods in 2004 has destroyed many houses and about 1 million people
became homeless. To a large extent, the patterns and causes of destruction
seem to result from poor technical knowledge and wrong perceptions.
1 Technocrats do not adequately support housing projects for low-income,
flood-vulnerable communities undertaken by NGOs and the government, and
houses are mostly owner-built without proper technical guidance.
1 One of the AUDMP findings of post disaster losses of the housing stock in
Bangladesh after 2004 floods is that most of these designs are prepared by
people who are not trained as building professionals, so when implemented,
many problems emerge.
1 The usual tendency is to apply the same model irrespective of context - for
example, the same house design is built on highland and low-lying flood-
prone areas.
1 In most cases, the cost is significantly prohibitive in terms of microcredit
recovery from poor people and this high cost prevents providing subsidized
housing to a large number of people who need them.
1 There is thus a need for developing housing which is appropriate for flood-
prone areas, where the suggested solutions are ‘cost-effective’ - that is,
rationalization of economy without compromising quality.
1 Those who work in the low-income housing sector in Bangladesh in general
are still to adopt such techniques.


TRADITIONAL MATERIALS USED:

FOUNDATION: In kutcha houses with usually bamboo and sometimes timber posts embedded directly into the earthen plinth. Extremely vulnerable and get damaged even in low intensity flood, thus requiring frequent maintenance.
In moderate to high intensity flood, especially if accompanied by currents, earthen plinths tend to get completely
washed off and have to be rebuilt. Bamboo or timber posts in saturated soil, especially during long duration or recurrent flood, get rotten at the base, thus weakening the entire structure of the buildings to damage by strong wind, differential settlement, sagging of roofing elements and doors, windows and wall elements developing cracks and losing alignment.
Frequent replacement of bamboo posts of kutcha houses is done regularly in flood-prone areas. The typical earthen
plinth in many semi-pucca houses also behaves similarly.

In semi-pucca houses, locally known as “dowa-posta”, is better at resisting erosion at the sides of a building, but the infill earth floor can experience settlement due to saturation and in prolonged flood can
become muddy, unusable and the mud can escape from below. At the same time, scouring of soil cover of the typically
shallow foundation of the perimeter brick wall can result in its instability and settlement.

WALLS:
ORGANIC/BAMBOO MATT: Typically in kutcha houses; semi-pucca houses also often have
bamboo mat walls. Organic materials (e.g. jutestick, catkin grass) have a lifespan of 2-3 years and bamboo mat 4-5 years. Decay can get accelerated in flood. In flood of high depth and moderate duration, the damage begins in the lower part of walls and hence weakens the walls and eventually results in
complete damage. Flood with strong currents can detach wall panels and wash them away, leading to partial or complete loss, especially if the connections to posts are weak.
EARTH: Used in kutcha and semi-pucca houses. Various types according to region, but not
prevalent in all areas. In monolithic construction, flood water can cause serious damage: once the base
gets affected, the entire structure is liable to collapse, often rapidly.

ROOF:
THATCH: Typically in kutcha houses, made from catkin grass, rice, wheat ormaize straw with usually bamboo and sometimes reed stalk framing. Normally has to be renewed every 2-3 years. Results in decay in houses of low height and during flood of very high depth and duration, if thatch comes into contact with flood water. In such conditions, if also
accompanied by strong current, thatching materials can get detached and washed away.
Secondary hazard often connected to flood is heavy rainfall, which can cause damage. Strong wind can also blow away thatching materials and damage frame.

APPROPRIATE CONSTRUCTION METHODS:

FOUNDATION:
-Stabilization of the typical earthen plinth can be carried out with a mixture of earth and cement.
-The proportion of cement to be added depends on the nature of the soil which can easily be tested on site.
-For soil with more than 40% sandy-silty particles, 5% cement additive is adequate. For soil with less sandy content, sand has to be added to raise the content above 40% and may require a somewhat higher
proportion of cement additive.

-Since very little load is imposed on the wall, the footing can be constructed with brick without the need for a concrete footing.
-Minimum 1:4 cement-sand mix should be used.
-Soil cover on the foundation should be thoroughly compacted and should
preferably have plant or grassy cover to prevent scouring during flood.
1 Infill should be of cement-stabilized soil to prevent muddiness, settlement due to saturation and loss of soil from below.

-Cheapest method for protecting from dampness lower end of bamboo/ timber posts typically embedded into the ground.
-Local method known by most villagers, but not widely practiced, and thus requires promotion.
-Molten bitumen, Mobil or sump oil, or a combination of these can be used.


WALLS:
There are different ways in which the bamboo matt walls of the super structure can be protected-
1. Detachable lower panels
2. Painting with Bitumen
3. Chemical treatment of Bamboo matt walls

To Strengthen earth walls there are two techniques-
Internal framework- Internal framework is provided so that there is no compromise with the structural stability, when the flood washes away the mud walls.
Cement Stabilization-Ideal cost saving method for inside walls in buildings with brick outer walls and damp-proof
plinths.
-Processing and preparation of mix similar to that of plinth stabilization
-Walls can be built by ramming inside wooden shuttering or by making blocks with a simple
brick mold.

ROOF:
CHEMICAL TREATMENT OF THATCH: -Similar to treatment of bamboo mats and battens
-Fibrous thatching material, such as catkin grass, rice straw, palm fronds, wheat, maize or sugarcane leaves needs to be soaked in preservative solution for only 12 hours (bamboo mats and battens 24 hours).