New obligations for Territorial Authorities to identify earthquake prone buildings
Territorial Authorities (TA) now have obligations to undertake investigations and identify buildings which may be earthquake prone. If a TA identifies a building as being potentially earthquake prone, then the building owner will need to provide the TA with an engineering assessment within 12 months.
What is an Earthquake Prone Building (‘EPB’)?
An EPB is one that;
- would have its ‘ultimate capacity’ exceeded in a ‘moderate earthquake’; and
- if the building was to collapse, the collapse would be likely to cause injury, death or damage to other property.
A building’s ‘ultimate capacity’ is the building’s probable capacity to withstand earthquake actions and maintain gravity load support. A moderate earthquake (in relation to a building) is one which is of the same duration as, but is one-third as strong as, the shaking which is used when designing a building as at 1 July 2017 (i.e. the potential shaking considered when consents get granted).
Structures that are commonly excluded from consideration as an EPB include residential buildings (other than those that are two or more storeys and contain three or more household units), farm buildings, bridges and tunnels.
What the EPB methodology identifies
The new EPB methodology sets the approach that TAs must take in identifying potential EPB. In high risk areas (such as Wellington) and medium risk areas (such as Nelson) the TA must identify a building as a potentially prone building if it falls under one of the below categories:
- Category A: Unreinforced Masonry building;
- Category B: Pre-1976 building of either 3 or more storeys or 12 metres or greater in height above the lowest ground level; or
- Category C: Pre-1935 building that is one or two storeys tall.
In low risk areas (such as Auckland) only the first two categories of buildings must be identified as potentially earthquake prone.
It will be up to each TA’s discretion as to whether they investigate any other buildings as being potentially earthquake prone, for example where buildings have non-ductile columns and/or buildings with no effective connection between primary structural elements. A TA has the ability to identify a building as being potentially earthquake prone at any time if it has reason to suspect it may be so.
Time frames for identifying EPB
The following time frames will apply to the identification of potential EPB:
- 5 years for High Risk areas;
- 10 years for Medium Risk areas; and
- 15 years for Low Risk areas.
These time frames will be halved for priority buildings. Priority buildings are buildings (identified by the TA) which are located within medium or high seismic risk areas and include those buildings that are to be used for emergency services, or which are schools. Buildings that have unreinforced masonry or are located on important transport routes may also be priority buildings.
Level of change in approach
Previously, TAs each had their own approach and process for identifying potential EPBs. As a result, the impact of the new methodology will vary for building owners depending on the location of their buildings.
Wellington City Council’s (WCC) previous policy of identifying potential EPB is similar to the process outlined in the EPB methodology. Following the November 2016 Kaikoura earthquake, the WCCreleased a Targeted Damage Evaluation that identified a large number of buildings around Wellington as being potentially earthquake prone. The approach taken by the WCC exceeded the requirements placed on them by the methodology. Therefore, buildings that have recently been assessed as not being earthquake prone should not require further assessments (unless the WCC becomes aware of an issue that prompts the need for further assessment).
Auckland Council’s previous policy staged investigations focusing on critical and higher-risk buildings (masonry). Older but lower-risk buildings only required an initial seismic assessment following a change in circumstances, such as a change in use. That approach sought to balance risk and cost, which is also a focus of the new methodology.
Engineering assessments for potential EPB
If a TA identifies a potential EPB, then they must request an engineering assessment from the owner of that building. The owner will need to arrange for an assessment to be completed within 12 months by a suitably qualified engineer at their own cost. Once the TA accepts the engineering assessment they will determine if the building means the criteria for an EPB.