Areas Without the 100mm Step-Down

Pool areas that have architectural constraints

NCC 2022 Volume Two 

Area of NCC Requirements:

• H2P1 – Rainwater management

• H2P2 – Weatherproofing

• H2F2 – Weatherproofing and dampness (Functional Statement)

The Challenge

Zero-threshold outdoor transitions are increasingly common in high-end residential design, particularly around pool areas where a seamless indoor–outdoor finish is a key architectural feature. The compliance issue is that the NCC’s Deemed-to-Satisfy (DTS) pathway typically relies on a minimum 100mm step-down at external thresholds to reduce the risk of water entering the building.

In this project, the proposed pool-area threshold did not include the standard step-down. This created a compliance gap and increased the risk that rainwater or surface water could migrate inside, potentially leading to dampness, deterioration of building materials, and moisture-related health concerns.

Because the design fell outside the prescriptive pathway, a performance-based solution was required to demonstrate that the threshold would still achieve the NCC’s intent for rainwater management and weatherproofing.

What This Really Means

The NCC is outcome-focused: water must be managed so it does not enter the building or cause dampness within the structure. Where a traditional step-down isn’t provided, the design must still prove that surface water will be intercepted, directed away, and safely discharged under normal and foreseeable wetting conditions.

The real compliance question becomes whether the threshold performs at least as well as a conventional DTS arrangement in preventing water ingress over the life of the building.

The Solution

A performance-based assessment was undertaken to confirm that the proposed zero-threshold pool-area design achieves the intent of H2P1, H2P2, and H2F2.

The assessment considered:

• How surface water is intercepted at the threshold and prevented from entering the building
• Whether drainage capacity and detailing are sufficient for expected rainfall and wetting events
• How water is directed and discharged so it does not accumulate at the doorway interface
• Integration with the surrounding finishes and waterproofing strategy to maintain continuity
• Durability, maintainability, and any inspection or upkeep requirements needed to preserve performance
• Whether the overall system outcome is equivalent to, or better than, a DTS 100mm step-down solution

Rather than relying on a single prescriptive geometric detail, the performance pathway evaluated how the threshold functions as a complete water-management system.

Why This Matters

The final report confirmed that the proposed threshold approach satisfies the NCC performance requirements for rainwater management and weatherproofing. Despite departing from DTS provisions, the design was shown—through documented evaluation and installation criteria—to effectively control surface water and prevent damp-related impacts.

This is a practical example of where performance solutions unlock modern, seamless design outcomes while still delivering robust, certifiable weatherproofing performance.

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