A staged flood in New Zealand has proven that “tanking” works as a means of disaster-proofing homes.

Engineers in New Zealand have staged a mock deluge to prove the effectiveness of “tanking” as a method for sparing homes from the ravages of flooding.

Tanking entails the use of a waterproof membrane to cover the whole exterior of a home during flood conditions, with specially provided flood guards installed in vents and door openings to prevent the ingress of water.

While the method is widely employed in the rain-sodden UK and has been included on a list of short-term flood defence measures drawn up by Christchurch City Council’s mayoral task force on flooding, its efficacy under local conditions has remained unproven until now.

In order to test the technology, a red-zone house in the Christchurch suburb of Avonside was subjected to artificially induced flood conditions. A waterproof barrier was erected around the periphery of the home and filled with water to a height of 900 millimetres.

According to Aecom civil engineer Stuart Sandy, the property had been selected specifically because of its compromised structural integrity, as it suffered from a number of severe cracks as a result of recent earthquake damage.

“We chose this house because it is a worst case scenario,” said Sandy. “If you can waterproof this one you can pretty much do any property.”

The results of the test have proved promising; despite the copious 900 millimetre high wall of water which besieged the Avonside house, tanking managed to prevent the entry of all but a small amount of water.

“We’re very pleased with the results,” said council transport and greenspace manager John Mackie.

Fake Flood

Mackie estimates that tanking could provide a reasonably economical means of preserving houses in low-lying areas from the massive damage caused by flooding, estimating the cost at between $15,000 and $20,000 per property. Around 80 homes in Christchurch are subjected to regular flooding as a result of their vulnerable positions.

The council is now working on the development of specifications for the installation of the technology in order to increase the ease and convenience of its deployment by homeowners.

  • Makes sense. One would think waterproofing membranes could be used for this purpose.

    I imagine the flood guards are installed as a permanent fixture?

  • The photo of the test shows a moat of water contained in a external pool built or formed against the building. In reality, whilst the outside skin of the building could be treated, there is no capacity to create a moat, so why wouldn't moisture flow or seep beneath the building/tank skin. Testing results premature. Try again.

  • Typically, tanking is used for below grade water proofing, where constant high moisture levels cannot be avoided. A cautionary note that water proofing a typical wood framed or wood cladded wall, without providing a drying potential can lead to rot and mold growth.
    When moisture is trapped behind the tanking material it cannot easily dry. I'd be hesitant to recommend a permanent "barrier" even with it's water hold out capabilities for flood protection.

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