When is a dwelling not a dwelling?

When it's Class 3!

If you’re working on residential buildings, you probably think of them as Class 1 or Class 2 dwellings. But in the NCC (National Construction Code), not all “dwellings” are treated equally.

Enter Class 3 buildings—a classification that trips up many in the industry when it comes to energy efficiency compliance.

This is especially relevant if you’re working on Specialist Disability Accommodation (SDA), student housing, retirement apartments, aged care, boarding houses, or serviced apartments.

What is a Class 3 Building?

According to the NCC:

Class 3 is a residential building other than a Class 1 or Class 2, which is a common place of long-term or transient living for unrelated people.

Examples include:

  • Specialist Disability Accommodation (SDA)
  • Student accommodation
  • Boarding houses or hostels
  • Workers’ accommodation
  • Certain types of serviced apartments and hotels

Why Does It Matter for Section J?

When your project is classified as Class 3, energy efficiency compliance is no longer covered by the residential (NatHERS) provisions.

Instead, you must demonstrate compliance with Section J of the NCC Volume One, which governs non-residential buildings.

This is a common trap for teams assuming that an SDA or student building can be modelled under NatHERS protocols. In reality, it requires:

  • Section J Deemed-to-Satisfy (DtS) report, or
  • J1V3 Verification Method (energy modelling).

Section J DTS vs J1V3 – What’s the Difference?

Section J Deemed-to-Satisfy (DtS):

  • A prescriptive checklist specifying minimum insulation R-values, glazing performance, roof colours, lighting, sealing, etc.
  • Suitable for simpler projects without design constraints.
  • Often requires higher specification glazing or insulation to tick every box.

J1V3 (Performance Solution):

  • A performance-based approach using energy modelling software.
  • Compares your proposed design to a reference DTS-compliant building.
  • Allows trade-offs (e.g., better wall insulation can offset higher glazing area).
  • Generally more design flexibility, especially on complex projects.

Why J1V3 is Often the Smarter Path for Class 3

Historically, DTS was the default option. But since NCC 2019, the stringency of Section J has increased significantly.

In many cases, a DTS approach for Class 3 projects now means:

  • Light-coloured roofs.
  • Smaller glazing areas.
  • Expensive thermally broken glazing.
  • Under-slab insulation.

A J1V3 assessment can often deliver compliance while:

✅ Avoiding some of these costly elements.
✅ Providing more flexibility in your architectural design.
✅ Reducing construction costs overall.

When Should You Engage an Energy Assessor?

If your project:

  • Is Class 3 or mixed-use with Class 3 components.
  • Includes SDA dwellings.
  • Has large glazing areas or unique design elements.
  • Needs clarity early in design on feasibility and cost impacts.

✅ Engage an energy consultant early.
They can advise whether DTS or J1V3 will be more practical and cost-effective.

How EcoResults Can Help

At EcoResults, we specialise in making Section J compliance clear, pragmatic, and efficient. Whether you need:

  • A straightforward DTS report,
  • A full J1V3 performance solution,
  • Or help understanding which path suits your project,

✅ We’ll walk you through the options and prepare clear, approval-ready documentation—without unnecessary cost or delays.

Need help or a quote? Call us or email us today—so you can get back to designing great buildings, and let us worry about the energy compliance.