Water tanks not properly restrained against earthquakes

External water tanks fed from the roof should be restrained to prevent the risk of them sliding or (with taller tanks) overturning in an earthquake. How this is done depends largely on tank size and location. Smaller tanks may have strapping. Larger tanks will have restraints around the base to stop them moving or may be set into the ground.

For details with exterior hot water cylinders, see here. For header tanks or hot water cylinders in the roof space, see here.

Causes

Restraining straps are loose

The tank was never restrained

Restraining straps and fixings are rusty

Listed under: Exterior, earthquakes, Section, durability, corrosion, rust, fixings and hardware

Cause

Restraining straps are loose

Repair

  • tighten straps and check fixings. Straps and fixings should be stainless steel

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Cause

The tank was never restrained

Repair

  • contact the tank manufacturer. Manufacturers frequently provide restraint kits for their products or provide guidance on what is required

  • many seismic restraint kits for large water tanks are a series of units that sit around the base of the tank and are bolted into the concrete pad

  • for smaller upright tanks that stand against a structure (such as a garage wall), a restraint system similar to a water cylinder restraint can be used. Use 25 x 1 mm stainless steel straps around the top and bottom of the tank (and in the centre on tanks over 200 litres), securely fixed to framing with a tension device to keep the straps in place

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Cause

Restraining straps and fixings are rusty

Repair

  • replace restraining straps and fixings with stainless steel

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