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Understanding NBS Seismic Ratings: What Does 67% Really Mean?

The full picture is more complex than a single number can reveal.

What is an NBS Score? The %NBS (New Building Standard) score measures how well an existing building would perform in an earthquake compared to current standards for new construction.

The Rating Scale Explained.

  • 67% and above: Considered acceptable seismic performance
  • 34-66%: Classified as an earthquake risk
  • 21-33%: Designated as an Earthquake Prone Building (EPB)
  • 20% and below: Also EPB, but with minimal earthquake resistance—essentially only resisting gravity with no lateral earthquake protection

Buildings classified as EPB are listed on the MBIE website, and owners receive mandatory timeframes for remediation based on their regional location.

The Changing Standards Challenge. Here's where it gets complicated. The measurement benchmark has evolved significantly:

2006 Standards: Focused primarily on structural elements

2017 Standards: Expanded scope to include all building components that could pose life safety risks—not just the main structure, but ceiling systems, facades, and other potentially dangerous elements

This creates a critical issue: where the reports originators can still choose which standard to apply, potentially "gaming" the system to achieve more favourable result.

Trust and Transparency Issues. Several factors can compromise the reliability of seismic assessments:

Limited Scope: Vendors commissioning reports may direct engineers to examine only specific building aspects

Restricted Liability: Report authors typically limit liability to the commissioning party, excluding other stakeholders from relying on the assessment

Potential Conflicts: The party commissioning the report may influence the scope and outcome

Real-World Consequences: The Oyster v MSC Case. This legal case demonstrates the serious implications of inaccurate seismic reporting. A building with an initially acceptable Seismic Assessment report later received a much lower %NBS rating in subsequent evaluations. The tenant cancelled their lease, leaving the building owner facing lost leasing revenue and substantial repair costs. Notably Justice Christine French questioned why the vendor wasn't also held accountable in the legal proceedings.

The Bottom Line for Property Buyers

A 67% NBS score should trigger careful scrutiny rather than automatic acceptance. Before commissioning an expensive second DSA report, consider these steps:

1. Review the existing assessment against current MBIE 2017 guidelines
2. Examine the report's scope and methodology
3. Understanding the building's true condition should be your primary goal
4. Calculate realistic remediation costs based on comprehensive assessment

Making Informed Decisions. Rather than relying solely on a percentage, focus on understanding your building's actual seismic vulnerabilities and the potential costs of addressing them. A thorough review of existing assessments often reveals more than immediately commissioning additional reports.

The question isn't just whether 67% is good or bad—it's whether you have enough reliable information to make an informed decision about your property investment. Contact us for expert guidance on understanding your building's true seismic condition

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