RIBA Flood Risk Housing
The close relationship between land development, drainage management and housing design is significant in our design approach to flood resistant housing. The design of houses in relation to their private open spaces, the street, the neighbourhood and overall masterplan are interrelated in minimising the damaging effects of flooding.
Our housing masterplan revolves around Sustainable Urban Drainage Systems (SUDS) which endeavour to mimic the natural movement of water from a development, thus reducing the risk of floods to houses. Instead of streets with cars, permeable surfaces and swales are designed along the front of houses which are connected to nnearby basins and retention ponds. They work as a system to retain storm water and runoffs from hard surfaces. The removal of the street also means that the large swathe of paved and green space in front of houses can potentially become a valuable social space for the community.
The proposed flood resistant single family dwellings are based on the terrace house typology, arranged back-to-back. This arrangement allows the creation of a raised public footpath at first floor level along the rear of the houses. During a flood, it becomes a safe access route for victims and emergency relief teams. Courtyards are inserted into each house to bring light and air to the rear ground floor living spaces, which will otherwise become inhabitable due to the back-to-back arrangement. Each courtyard will be landscaped and its porous surfaces are effective in reducing the quantity of surface water run-off. To further reduce the rate of run-off, roof gardens and rain-water harvesting systems are introduced to each house.
The ground floor levels of each house are split by cut and fill of the site. The front half has a level 300mm whereas the rear half is at 1200mm above ground. This means that only half the ground floor of the house will be submerged in water during a major flood. The houses are designed to resists entry of flood water at levels below 300mm, but for higher levels, a water entry approach is adopted. This strategy gives time to occupants to move their belongings to a higher ground before the water actually enters the house. The kitchen – a space with the highest number of electrical appliances – is located on the higher ground level at the rear.
The construction of each house needs slight modifications from standard practice. For example, raised door thresholds prevent low water entry and engineering brick foundation walls are used for their proven ability to prevent water ingress compared to other types of masonry wall. For the water entry strategy, the resilience of materials and their locations are of prime importance. For example, ceramic tiles floor finishes will be used and insulation is the ‘closed-cell board type’, fixed above the ground floor slab and on the internal faces of the external walls. While these boards are moisture resistant to a certain extent, their location facilitates easy replacement if damaged by prolonged floods.