Retrofitting Seismic Restraints

A roof space water tank unrestrained

Roof space and roof top water tanks (or header tanks) are more common than you might think, and a large proportion of these are still not properly restrained against earthquakes.

According to the Building Research Association of New Zealand (BRANZ) there is an estimated 232,000 header tanks in roof spaces and 59,000 on roof tops – approximately 93% of these are not properly restrained.

Even if they are no longer in use, header tanks can be potentially dangerous in an earthquake if they fall through the ceiling or off the roof.

Building Code clause B1 requires water tanks including header tanks to be adequately supported including seismic restraint chocks. Retrofitting restraints to older tanks where they do not exist is highly recommended.

Some ready-made kits are available from hardware stores that include galvanised or stainless steel straps, screws, tensioning devices, earthquake brackets and bolts for header tanks up to around 700 litres.

Another option is to install 25 x 0.75mm or similar galvanised or stainless steel restraining straps, fixing the tank to roof framing to prevent it overturning or falling off the roof in an earthquake.

Extremely small tanks of less than 90 litres can be restrained with blocks around the base and a single strap around the tank. Use two straps for cylinders of up to 200 litre capacity and a third strap in the centre for larger tanks. The top and bottom straps should be no more than 100mm from the ends of the cylinder.

For more information on header tanks or to talk to one of our building team you can call 0800 SELWYN (735 996) or email contactus@selwyn.co.nz.

Last modified: 01 May 2024 7:18am