There are specific rules around the definition of earthquake-prone buildings and the requirements for them to be seismically strengthened.
A building is defined as earthquake-prone “if it will have its ultimate capacity exceeded in a moderate earthquake, and if it were to collapse, would do so in a way that is likely to cause injury or death to persons in or near the building or on any other property, or damage to any other property."
The provisions do not apply to individual family homes, but do apply to residential buildings that are at least 2 storeys and:
- house three or more household units, or
- are used as a hostel, boarding house etc.
Key elements of the regime include:
- A publicly-accessible and searchable register of earthquake-prone buildings buildings.
- A document, EPB methodology – The methodology to identify earthquake-prone buildings, sets out how TAs and engineers can identify, assess and make decisions on potentially earthquake-prone buildings. This sets out how TAs and engineers can identify, assess and make decisions on potentially earthquake-prone buildings.
- The threshold for defining an earthquake-prone building remains, with amendments including that it can apply to parts of buildings. (An earthquake-prone building is often referred to as one that is less than 34% of the new building standard – see below.)
- EPB notices, which show earthquake ratings, must be placed on earthquake-prone buildings.
- New Zealand has been divided into 3 seismic risk areas – low, medium and high – based on the seismic hazard factor (‘Z’ factor).
Based on these risk areas, timeframes have been set for TAs to identify earthquake-prone buildings and for owners to strengthen or demolish them:– in high-risk areas (such as Wellington) buildings must be assessed by 1 Jan 2020 (priority buildings) or 1 July 2022 (other buildings). From the date owners are notified their building is earthquake-prone, they must carry out seismic work within 7.5 years (priority buildings) or within 15 years (other buildings)– in medium-risk areas (such as Hamilton or Nelson) buildings must be assessed by 1 July 2022 (priority buildings) or 1 July 2027 (other buildings). From the date owners are notified their building is earthquake-prone, they must carry out seismic work within 12.5 years (priority buildings) or 25 years (other buildings)– in low-risk areas (such as Auckland) buildings must be assessed by 1 July 2032. From the date owners are notified their building is earthquake-prone, they must carry out seismic work within 35 years– 10 years can be added for registered heritage buildings– low-risk, low-usage buildings can be exempted
- A new category of priority buildings in medium and high-risk areas has been defined. These buildings – schools, emergency facilities etc. – must be identified and strengthened earlier than other buildings
- There are particular requirements around securing unreinforced masonry building parapets and facades. You can find details on MBIE’s building performance website.
Engineers carrying out seismic assessments of potential earthquake-prone buildings must use the 2017 Engineering Assessment Guidelines (“the Red Book”). There is a revised section C5 (“the Yellow Chapter”) currently (mid-2020) being tested that incorporates recent knowledge. Owners who have already obtained an assessment using the Red Book do not need to obtain a further assessment using the Yellow Chapter.
Engineering New Zealand says that “a %NBS score evaluates the performance of a particular building over a range of earthquakes, in terms of protecting life. It’s calculated as part of a seismic assessment of a building.
%NBS does not measure compliance with the current Building Code. If a building scores 100%, it doesn’t mean it fulfils all the requirements of the Building Code. It means that the building should perform in a way that meets the minimum seismic performance objectives of the Code in terms of protecting people.
A %NBS rating doesn’t measure a building’s ability to function after an earthquake. It says nothing about the damage that building could be expected to sustain or whether it will be able to be used again.”
BRANZ has developed an online resource around seismic resilience.
MBIE has produced a short video introducing the system for managing earthquake-prone buildings.