Threshold Heights

Surface finishes that impact weatherproofing

NCC 2022, Volume 2

Area of NCC Requirements:

• H2P1 – Rainwater managment
• HP 3.3.3 (b) (ii) - Drainage

The Challenge

Pedestal paver systems are a popular choice for alfresco areas because they create a premium finish, allow services and drainage to be concealed, and can make levels easier to manage across external spaces. The catch is that pedestal systems often change how “clearance at openings” is achieved at sliding doors.

In this NSW project, pedestal pavers were proposed at a ground-floor alfresco adjoining an internal sliding door. The finished external surface did not present the typical clearance arrangement that the Deemed-to-Satisfy (DTS) provisions rely on to reduce the risk of surface water reaching and entering the building.

That departure created an approval risk: if water ponds near the threshold, bridges the junction, or bypasses drainage controls, it can cause loss of amenity, internal dampness, and deterioration of building elements—exactly what H2P1 is intended to prevent.

What This Really Means

The NCC isn’t protecting a number on a drawing—it’s protecting the building from water entry during foreseeable rainfall events and site wetting. Where DTS clearance can’t be achieved in the “usual” way, the design must still show that water will be intercepted, managed, and discharged so it doesn’t enter the building and doesn’t create dampness or deterioration over time.

The Solution

A performance-based assessment was prepared to demonstrate that the alfresco-to-dining sliding door interface achieves the intent of NCC 2022 Volume Two, Amendment 1 – H2P1, despite the non-standard external surface arrangement.

The assessment considered:

• Whether water is prevented from ponding at the threshold under normal and foreseeable wetting conditions
• How water that reaches the external surface (including water that passes through the paver layer) is managed and directed to a drained point
• How the waterproofing and drainage strategy functions as a complete system at the substrate level rather than relying on the finished surface alone
• Threshold detailing principles that prevent “bridging” of water from the external zone into the internal floor zone
• The practicality of verification and ongoing maintenance so performance is maintained over the life of the building

The focus was on demonstrating an equivalent or better outcome to the DTS intent: reliable water control at the opening through system design, verification steps, and maintainable drainage elements.

Why This Matters

The final report confirmed that a pedestal-paver alfresco can be compatible with NCC weatherproofing intent at a sliding door opening when the system is assessed holistically and supported by appropriate performance controls.

It’s a practical example of where performance solutions add real value: modern external finishes can still be approved without forcing a redesign—provided the water-ingress risk is addressed in a defensible, buildable, and maintainable way.

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