Weatherproofing Circular Skylights
Demonstrating NCC compliance through Performance Solutions.

Weatherproofing Considerations for Non-Standard Rooflights

NCC Volume Two

Area of NCC Requirements:

• Part H2 – Damp and Weatherproofing
• H2P2 – Weatherproofing

The Challenge

Skylights are a popular design feature that allow natural light to enter internal spaces, improving both the appearance and functionality of a room. However, from a building compliance perspective, not every skylight system has a clear Deemed-to-Satisfy pathway under the NCC.

For this project, a circular skylight was incorporated into the roof design. The challenge was that circular skylights are not specifically recognised as a standard DTS roof covering under the NCC.

Because there was no direct prescriptive pathway available, the proposed installation needed to be assessed to ensure it would provide adequate protection against water ingress, moisture build-up, condensation and long-term weather exposure.

What This Means

The NCC weatherproofing provisions are intended to ensure that external building elements, including roofs and walls, can effectively manage rainwater and prevent moisture from entering the building.

Where a product or system is not clearly addressed by the DTS provisions, it does not automatically mean the design cannot be used. Instead, compliance must be demonstrated through a Performance Solution.

For a circular skylight, the key issue is whether the system can perform to an equivalent standard when compared with a conventional DTS-compliant roof covering.

This requires consideration of the skylight unit, flashing design, roof junctions, water drainage, insulation, condensation control and evidence that the system is suitable for Australian weather conditions.

The Solution

A Performance Solution was developed using a certified circular skylight system.

The proposed design was reviewed against the intent of the NCC weatherproofing requirements and included:

• Flashing details designed in accordance with relevant Australian Standards
• Drainage provisions to assist with rainwater management around the skylight
• Insulation and condensation control measures
• Manufacturer installation requirements and technical specifications
• Certification and supporting evidence to demonstrate the suitability of the system
• Comparative assessment against conventional DTS roof covering performance

Based on the available evidence and expert assessment, the circular skylight system was considered capable of achieving an equivalent level of weatherproofing performance to a DTS-compliant roof covering.

The certified system, together with the supporting installation details, provided confidence that the proposed skylight could resist water penetration and maintain the required level of weatherproofing performance.

Why This Matters

The final assessment confirmed that the circular skylight installation satisfied the relevant Performance Requirements for weatherproofing under the NCC.

By using a certified system, relevant Australian Standards and appropriate construction detailing, the project team was able to demonstrate that the skylight could be installed without compromising the weatherproofing performance of the roof.

This project highlights the value of Performance Solutions for architectural features that fall outside standard DTS provisions.

Circular skylights can provide excellent design outcomes, but they must be supported by the right technical evidence, certification and installation details to achieve NCC compliance.

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