Constructing Flood Resistant Houses in Kerala
The most important possession of every family is their house. The catastrophic Kerala floods have damaged this asset. Reconstructing the damaged houses is not the ideal solution. Based on my experiences rehabilitating communities following the earthquakes in Latur and Bhuj, the present and future houses must be made flood resistant. Many homes that appear to be in a state of disrepair may be renovated and brought back to life. Disasters are increasing, and the future floods might not be a 50 year or 100-year event. Hence, this blog offers a few straightforward, innovative and cost-effective measures of reducing the vulnerability of houses to floods in future. It explores various flood-resistant building techniques to protect houses from the damage caused by floodwater.
List of Contents
1. Ways to Construct Flood Resistant Houses
1.1 Site Planning
The rising dampness in the building will become less problematic if the land is sloped away from the building. To guarantee that the rainfall drains away from the structure, the ground should slope away from it. Close to the external walls, all dirt and loose earth should be removed. The plinth height should be kept to a minimum of 450 mm.
1.2 Deep Foundations
Shallow foundations can become unstable due to the displacement of soil during floods. The foundation of a flood-resistant house must be deep to stop the movement of the sub-strata and ultimately stop a foundation failure. In addition to matching the standards of a flood-resistant home's foundation, piles or columns are employed to lift the structure above the prescribed flood level. Such elevated development helps in preventing floodwater from entering the building.
1.3 Plinth Protection
The soil near the foundation may be removed by the receding floodwater. Plinth protection is typically done by laying a 75–100 mm layer of plain cement concrete along the building's border. The plinth must be protected to prevent/reduce water penetration by capillary action from reaching the plinth wall and in turn reaching the floor level. Even in areas, where plinth protection is done, the water might find entry into the foundation and therefore, enter into the soil beneath the floor. This shall be avoided by proper filling around the building.
1.4 Lofts and Balconies
In many houses, floodwater rose to an adult person’s height. Taking advantage of the sloping roof in single-storied homes, a loft may be converted into a short-term flood refuge room in such homes. They can be used to house valuables, persons, and animals until the rains cease. If building a staircase to access it is not feasible, a ladder similar to the one in traditional Kerala houses can be used.
When the entire ground floor of a building is underwater, rescuing trapped people is easier in the case of houses with first floor balconies.
1.5 Positioning of Staircase
The staircase plays a chief role in houses in flood-prone areas. The internal staircase may not be effective as an escape route if floodwater enters the home to a significant height because the interior doors remain blocked until the water drains completely. In such instances, the rescue squad can board individuals to safety via an exterior stairway. The staircase should be wide enough to take everything to the first floor, in case of inundation of the ground floor. For instance, if there are cattle in the house, then a wider external staircase may be appropriate.
1.6 Location of Water tank
A residence in a flood-prone area should have its water tank elevated as high as possible so that water is available even if the power supply is cut off. It can be located on a terrace or above the headroom. If it is an underground sump, it should be elevated as high as possible so that the floodwater does not enter the tank.
The rainwater can be harvested on the roof/or at a high level to ensure continuous water supply to the house.
1.7 Protecting Electrical Services
The power supply will be disconnected during the floods to avoid damages. It is problematic to restore power even after the floods when the electrical system gets damaged. In new buildings, the distribution board (DB box) of the electrical supply can be raised above the maximum flood level although electricity board engineers want it close to the ground for inspection and reading.
During floods, a solar panel with an inverter will make sure that at least the lights and mobile phones can be made functional.
1.8 Sewage System
The mixing up of sewage and the floodwater will not happen if the sewage is raised above the flood level of the region. Providing a non-return valve also ensures that the sewage does not back up into the toilets.
Toilet floors must be elevated in new homes to prevent sewage from rising into toilets.
2. Extensions in One Storey and Two Storey Houses
During the Kerala flood 2018, water even entered the first floor of many houses, which makes the single-storey structures completely unsafe. Many single-story dwellings in Kerala are vulnerable to flooding in the future, resulting in loss of life and property. In such cases, a two-storey extension can be made adjacent to the present house with a staircase outside. Objects such as furniture, television, electrical equipment, documents etc., can be stored on the first floor of this house at the time of a flood.
In the case of two-storied houses, where water flooded the first floor, a three-storied extension of 200 sq. ft on each floor can be made with an external staircase.
3. Flood Resistant House Design for New Constructions
One possibility is to build a stilt house with concrete columns to protect them from flooding. A staircase has to be constructed to gain access to the upper floor of the house. The stilt floor can be used for parking, work-shed or cattle-shed, etc. The stilts might be cheaper when compared with the cost of elevated development which has to be filled completely.
Buildings built using alternate technology such as rammed earth and stabilised earth blocks will be good enough to withstand the floodwater. But the ordinary earth blocks will become weak with prolonged submersion of water.
Bamboo may be used as a construction material. But it must be carefully constructed to include termite protection, avoidance of touch with the ground, and a link between the roof and the walls, among other things.
4. Water Resistant Materials for Kitchen Shelves and Wardrobes
Solid timber will withstand water the most, followed by marine-grade plywood and exterior-grade plywood. Medium-density fiberboard (MDF) and particle boards have very little resistance to immersion in water. In flood prone areas, moisture-resistant adhesives must be used.
Climate change and global warming are real threats. We have to face the reality of the rising sea levels. The thrust of the disaster recovery plan in Kerala shall be to avoid future disasters. Kerala must remain an attractive place. The decision of building in flood prone areas shall be taken based on the cost-benefit analysis. The durability of a building is highly dependent on the quality of workmanship and the design details.
It is vital to follow guidelines to mitigate the effects of floods. There are various cases where subsequent floods caused a more devastating impact because the buildings were already damaged by the earlier flood. Therefore, the following steps are indispensable to fight the impacts of natural disasters:
Avoid improper and haphazard landfilling.
Avoid construction in floodplain areas.
Follow proper planning and design methods.
Good quality workmanship is to be followed by regular maintenance.
The successful building of flood resistant houses in Kerala will depend on how we take disaster relief measures to overcome future floods.