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Circular Skylight

Circular Skylight

Skylights and DTS Requirements

Circular Skylights and Weatherproofing  



NCC 2019 Volume 2, Amendment 1

Area of NCC Requirements:

  • Part 2.2 – Damp and Weatherproofing
  • P2.2.2 – Weatherproofing of Roofs and External Walls


The Challenge

Skylights bring natural light into interior spaces and can transform the quality of a room. But from a compliance perspective, not all skylights fit neatly into the NCC’s Deemed-to-Satisfy (DTS) framework.

In this project, a circular skylight was proposed as part of the roof structure. The issue? 

Circular skylights are not recognised as a DTS roof covering under the NCC. Without a prescriptive pathway, the design risked being deemed non-compliant and raised concerns about water ingress, condensation, and long-term durability.


What This Means

The NCC’s weatherproofing provisions are about more than just stopping leaks—they ensure that roofs and walls can reliably manage rainwater, resist dampness, and maintain healthy internal conditions over time.

When a building element like a skylight doesn’t appear in the DTS list, it doesn’t mean it can’t be used. It means the responsibility shifts to a performance solution to prove the system will perform as well as, or better than, the standard provisions. For skylights, that proof hinges on proper flashing, drainage, insulation, and certification that the system resists moisture under Australian conditions.


The Solution 

A performance solution was prepared using a CodeMark-certified circular skylight system. The design addressed NCC intent by:

  • Incorporating detailed flashing in line with Australian Standards
  • Providing drainage and insulation detailing to prevent water penetration and condensation
  • Backing the system with manufacturer specifications and CodeMark evidence of suitability

Expert judgement and comparative analysis confirmed that the proposed skylight installation provided equivalent, and in some respects superior, weatherproofing performance compared to prescriptive DTS roof coverings.


Why This Matters

The final assessment concluded that the skylight met the performance requirements of P2.2.2. 

With CodeMark certification and compliance with relevant Australian Standards, the solution gave certainty to the builder, designer, and certifier that the installation was both watertight and NCC-compliant.

This case shows how performance solutions can unlock architectural features like circular skylights—features that fall outside DTS rules but deliver strong design outcomes. With the right certification and detailing, innovative roof elements can achieve compliance while enhancing the aesthetics and functionality of a home.


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