Engineering New Zealand (on behalf of the Joint Committee for Seismic Assessment and Retrofit) is seeking feedback on proposed changes to three sections of the Non-Earthquake-Prone Building (non-EPB) Seismic Assessment Guidelines:

These changes are being proposed to improve the clarity of the Guidelines and consistency of assessments.

Engineering New Zealand invites you to have your say on the proposed changes to the Guidelines from Tuesday 19 August 2025 until Sunday 14 September.

To provide feedback on the changes, please complete the submission form and email it to nonEPBguidanceconsultation@engineeringnz.org.

Comments will be compiled for the Joint Committee’s review – and the Committee expects to publish the final version of the Non-EPB Seismic Assessment Guidelines with changes by the end of 2025.

Updates to the Non-EPB Seismic Assessment Guidelines are not a part of the Earthquake-prone Building System Review that the Ministry of Business, Innovation and Employment (MBIE) is currently undertaking. Updates to the Guidelines were underway before the EPB System Review was announced in 2024.

Consultation on section C4 (Geotechnical Considerations)

Changes have been made to Version 1 July 2017 of Section C4: Geotechnical Considerations to improve clarity of the guidance and to promote consistency in its application. Changes have also been made to further encourage focused specialist geotechnical input to seismic assessment of existing buildings.

Achieving this requires a collaborative effort between geotechnical and structural engineers. Structural and foundation engineers are encouraged to review this guidance and assess how they can improve their collaborative efforts.

You can read the full C4 document available for consultation here.

Summary of key changes

The main changes from Version 1 July 2017 of Section C4 are:

  • Restructured to improve readability
  • New or substantially changed sections:
    • Key principles
    • Selecting geotechnical parameters
    • Guidance on undertaking a desk top study
  • Consideration of SSI effects, including:
    • Initial assessment (A filter, does SSI matter?)
    • Guidance on more detailed assessment (if required)
    • Allowing for spatial variation of soils
    • Allowing for beyond peak resistance (sensitive soils)
    • Allowing for degradation of pile side resistance with cyclic loading.
  • Identifying and allowing for geotechnical step change, including:
    • Why, when and how to allow for geotechnical step change
  • Staged reporting (to encourage a collaborative approach)
  • Appendix of geotechnical step change worked examples
  • Appendix of worked examples allowing for uncertainty

Impact on %NBS Assessment

While the changes were not intended to directly impact the assessed %NBS, the enhanced clarity may lead to less conservative interpretations of the guidance in certain cases, potentially resulting in higher assessed %NBS. The geotechnical step change factor has been reduced from 2 to 1.5, unless the potential consequences are extreme. As a result, the assessed %NBS could increase in some instances. These potential adjustments to the assessed %NBS only apply to geotechnically dominated assessments or certain interactive assessments—not all assessments.


Section C8 (Unreinforced Masonry Buildings)

Changes have been made to section C8: Unreinforced Masonry Buildings to update and improve the guidance.

In most cases the new information will provide expanded clarification or is addressing an identified omission in the 2017 issue of C8.

During the Joint Committee’s review process, errors were identified in the charts of Appendix C8C for out-of-plane response of parapets and one-storey walls. These errors have been corrected in the version of C8 released by ENZ for consultation. There were no errors in the relevant guidance formulas and text in C8.8.5 – the identified error only impacts assessments that used the Appendix charts. Further information is provided below on the possible impact of these errors.

Corrected charts have been provided in the updated C8 out for public comment and will be included in the final Non-EPB Seismic Assessment Guidelines when they are released, likely in Dec 2025.

You can read the full C8 document available for consultation here.

Summary of key changes 

Unreinforced masonry building (URM) construction can be vulnerable to earthquake shaking because of its high mass, lack of integrity between elements and lack of deformation capability. This 2025 update of C8 includes:

  • Expanded details regarding the treatment of cavity walls
  • Greater discussion regarding the selection of boundary conditions for out-of-plane wall response
  • A procedure for the detailed assessment of masonry gables, including the preparation of charts to facilitate the assessment process
  • Expanded clarification for how to select an equivalent frame when assessing the in-plane response of a penetrated unreinforced masonry wall
  • Expanded details on horizontally-spanning masonry walls, including advice on strongbacks
  • Corrections to the charts in Appendix C8C.

The changes also include less extensive modifications introducing:

  • Brief comments on how to assess unreinforced masonry parts that are found in building types that are not predominantly of unreinforced masonry construction.
  • Brief comments on how to subdivide a complex URM building into more macroelements
  • Procedure when an unreinforced masonry wall is a basement and subjected to soil pressures
  • Aspects to consider when a concrete ring beam or bond beam is present.
  • Further advice on aspects related to toe crushing.

Impact on %NBS Assessment

Several changes in the 2025 issue of C8 will influence the calculated %NBS score. These changes are:

  1. Criteria for rocking displacement have been relaxed.
  2. Errors were identified and have been corrected in the charts for face-loaded walls. There was no error in the guidance formulas and text, so this error only impacts assessments that used the charts. This correction will elevate the evaluated %NBS score when using the new charts.
  3. Errors were identified and have been corrected in the charts for the out-of-plane response of vertical cantilevers (parapets and some one-storey walls). There were no errors in the guidance formulas and text, so this error only impacts assessments that used the charts. Feedback indicates that most assessors code the formulation into spreadsheets, so only a subset of all assessments relied only on the charts.

The error identified in Item 3 is unconservative and is the only change that will potentially result in a lower calculated %NBS score. There is a narrow range of parapet configurations which would have previously exceeded 33% using the old charts and would now score below 33% using the corrected charts. For example, for a 2-leaf parapet and soil class C, the parapet height would have the range shown in the table below.

Seismic Zone

Low

Medium

High

Seismic Zone Parapet height (mm)

Low 700-1600

Medium 450-700

High 250

Most parapets would be over 250mm and typically in High zone would have braced regardless of assessment outcomes or would have restraint from the likes of gutters or flashings if lower than 250mm. Few Medium zone parapets are likely to be at this height: parapets are most commonly less than 450 mm or more than 1200 mm high. Low zone parapets represent the greatest residual risk. This risk only exists if the charts were used to assess parapet stability rather than the mathematical formulation (which engineers often carry out by standard spreadsheet).


Section C11 (Reinforced Concrete Masonry)

This new section offers detailed guidance for assessing Reinforced Concrete Masonry (RCM) buildings. It includes an overview of RCM construction history in New Zealand, recommendations for site testing, probable material properties, and methods for calculating the capacity of structural elements.

You can read the new C11 document available for consultation here.

Summary of C11 content

Section C11 addresses an acknowledged gap in the existing guidelines, making Detailed Seismic Assessment ratings for RCM buildings faster and easier to determine. This section is particularly relevant to low-rise RCM buildings, which are common in New Zealand. The guidelines cover the recent history of RCM in New Zealand, known seismic weaknesses, and methods of assessing the capacity of RCM elements.

Key elements of the section include:

  • Seismic Response Understanding: Engineers are provided with an understanding of the underlying issues associated with the seismic response of RCM buildings, including inherent vulnerabilities and weaknesses.
  • Building Practices and Observed Behaviour: Typical building practices are detailed and the observed behaviour of RCM components during earthquakes, including structural deficiencies, are discussed.
  • Material Property Guidance: Guidance for determining key material properties such as masonry compressive strength is provided. Options are provided for avoiding site testing by assuming low strength properties or adopting greater strength through confirmation of RCM construction properties via site inspection.
  • Assessment Tools: Supplementary information is provided to allow the application of assessment tools from the existing Section C5 and other sources.