For many the enduring image of the Queensland floods are the overhead shots of rooftops, half- submerged under a churning wash of turbid brown water. Later as the level receded, the extent of the damage began to be gauged; with the ruined content of houses piled up next to the eviscerated hulks of frail looking buildings.
According to statistics from the Insurance Council of Australia, about 95 percent of significant catastrophes are a result of extreme weather. Building codes do address this issue, though surprisingly few provisions are made for flooding. An odd omission when considering that an estimated 400,000 dwellings around the country are situated on flood-prone land and that 30 percent of annual costs relating to natural hazards in Australia results from flood damage.
During the half year since the January floods various organisations and think-tanks have been set up in order to help facilitate the rebuilding of Queensland, with a focus on minimising future damage.
In an article published in The Australian, the Brisbane based architect Michael Rayner pronounced three schools of thought relating to the rebuilding of Brisbane, “retreat, defend or redesign”. For many a retreat is not an option and so the focus will involve either strengthening a house’s defences or else redesigning in order to better manage floodwater.
Image courtesy Cox Rayner
Design
With this in mind, homeowners and architects face a set of decisions in terms of the design approach to the rebuild project. A protected building in a flood-prone area can either be one or a combination of the following:
• Flood resistant, also known as dry flood-proofing, which requires the building to be both watertight and able to withstand high levels of hydrostatic pressure.
• Flood resilient, also known as wet flood-proofing, where the materials used need to be able to withstand exposure to fast flowing floodwater, with only cleaning or minor repairs required after the water recedes.
• A raised house, either as a high-set or medium-set house, requires the floor to be raised above the maximum flood level height and for the structure to withstand the force of the floodwater.
In most cases the flood resistant approach will be impractical, in part due to the lead time involved in developing such a project, but also because of the higher costs of dry flood-proofing.
Among the huge mass of data gathered by Brisbane architect James Davidson for Emergency Architects Australia (EAA) in the wake of the floods, was information pertaining to demographic vs. damage. The findings showed that many of the worst effected areas, such as Goodna and East Ipswich, were home to families less likely to have sufficient insurance cover and therefore unable to afford expensive rebuilds.
Emphasis should therefore be on rebuilding homes that are more resilient to floodwater, either by moving living quarters above the flood level or by designing buildings to better withstand flood inundations.
Materials
Speaking of the homes that bore the brunt of the January floods, Davidson described the majority of properties as slab-on-ground with cavity wall systems. And in many of these cases he found evidence of buckled floorings, the shifting or cracking of slabs and swollen composite materials.
Over the last few months the Queensland Government has published various guidelines and factsheets, identifying repair and rebuild techniques for flood affected residents. The information covers a broad set of considerations and advice, from the cleaning of mud, silt and debris from the property, to building products with a higher water resistance rating.
Some of the suggestions for water resistant products include:
• Replacing kitchen plasterboard wall linings with fibre cement sheeting, which can then be tiled over with waterproof adhesive
• Kitchen bench tops could be replaced with stone or reconstituted stone products
• Hardwood framing is better suited to withstand flood conditions and should be considered over materials such as particleboard and pine
• Glass is an easily cleaned, water resistant product and can be used to create a feature wall
• Replacing insulation batts in your wall cavities with plastic or polystyrene insulation boards.
In addition, the Department of Local Government and Planning has released a table of Building materials that may help improve the performance of your house both during and after a flood event. The categories include Walling and ceiling lining; Doors; Bolts, hinges, nails and fittings; Windows; Insulation; and Floor coverings and are split between higher water resistance and lower or no water resistance.
The preferred materials tend to follow a commonsense theme of being smooth and non-porous, such as concrete, galvanised steel sheets, glass blocks and plastic sheeting with waterproof adhesive; in place of particleboard, non-durable solid wood and gypsum plaster. Focusing on denser materials that offer more resilience to water damage, improves a building’s chances of both withstanding the initial impact of a flood and then returning to its original condition as the water recedes.
