earthquake copy2 blog

Evaluating the earthquake risk when finding your next workspace

12 February 2019, by Paul Mautz

More than two years ago on from the Kaikoura earthquake, our Capital’s property market is still dealing with the impact.

The high demand for ‘safe’ workspaces is ongoing. Most clients want simply to be reassured their workspace is safe for their people and meets an acceptable seismic standard (as measured by the National Building Standard or NBS). What they don’t understand is what all the jargon and percentage ratings really mean.

So, here’s a simple break down below.

Earthquake ratings – what do they really tell us?

NBS stands for National Building Standard, and is a measure of how a building compares to the seismic strength of a new building constructed to the current building code.

The basics

If a building has an NBS of 50%, then there is a likely risk it could be significantly damaged in the event of an earthquake that was half as strong as an earthquake a new building is designed to withstand. In Wellington, office buildings are built to withstand a 1 in 500 year earthquake. A building with a 50% NBS would risk significant damage or collapse in the event of a 1 in 100 year quake (the scale is exponential).

What do the percentages really mean?

Between 34% and 67%, The NZ Society of Earthquake Engineering (NZSEE) considers the building an ‘earthquake risk’. Above 67%, a building is considered to be medium to low risk.

The risks to your organisation

The following table is a useful way to understand the level of risk associated with the various NBS ratings:

% NBS rating 

Approx. risk to new building 

Probability over a 12 year lease period of an earthquake occurring that will exceed the capacity load of a new building 

Risk description 




Low risk 


2 times 


Low risk 


5 times 


Medium risk 


7 times 


Medium risk 


10 times 


High risk 


More than 25 times 


Very high risk 


Source: Beca


The table shows that being in a building rated 50% (which is considered a medium risk) there is an 11.4% chance during a 12 year period of experiencing an earthquake that exceeds the ability of the building to withstand it.

Such a building is likely to be seven times more at risk than a new building when it comes to the likelihood of major failure.

What about the buildings rated below 34%?

Any building below 34% is considered ‘earthquake prone’. New legislation now applies to earthquake prone buildings, primarily around identifying the buildings and timeframes for strengthening.

There is a perception that earthquake prone buildings can’t be occupied, but that’s not correct. They can be occupied, it’s just a question of safety. The NZSEE have provided guidance that a building with a rating less than 34% NBS would be a highly risky building to occupy. There are also consequences under the Health and Safety in Employment Act if employers do not take practical steps to minimise hazards in the workplace. An earthquake prone building would be a considered a hazard.

What recent earthquakes have shown us

While these statistics make sobering reading, things do not always play out like this way in real life!

Christchurch witnessed a 1 in 2000 year earthquake in 2011 and Wellington had a 1 in 100 year event in 2016. The damage sustained to medium risk and high risk buildings did not match these stats, although a number of buildings did need to subsequently come down as a result of damage or as a safety precaution.

There are no guarantees how a building with eventually perform in a major shake, but the NBS rating system seems to be the best tool we have for now to help us make decisions on managing safety obligations in the workplace.




About the author

Knows a lot about 1970’s music. Wears a hat. In-house quiz master. Sauv Blanc and MU fan. Prefers to spend winters in Europe. Learning the guitar.

Paul has been a senior member of our team since 2004 and specialises in premises procurement and leasing. With 25+ years' experience in the commercial property sector, he's been involved with a number of large leasing transactions, representing clients in project leadership and tenant representation roles.

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