While NCC 2022 brought about many changes, one of the most significant areas of change are the amendments to Condensation Management. NCC 2022 ABCB Housing Provisions has introduced Part 10.8.3 Ventilation of roof spaces; requiring some form of dedicated roofspace ventilation projects within Climate Zones 6, 7, and 8.

**Figure 1:** South Australian Climate Zones 5 & 6

**Figure 2:** Victorian Climate Zones 6, 7 & 8

I won’t be explaining the compliance and construction impacts of this change in this article because I won’t be explaining it as well as Clarence Macalister did here in his article titled NCC 2022 Roof Ventilation. It’s well worth a read and will serve as the prerequisite knowledge for this particular article.

In this article, I wanted to show you what options we have available to us within NatHERS, specifically in HERO V4.1, and how these impact the star rating and the on-paper performance of the home.

Laying Out the Experiment

The goal of this experiment is to showcase two common roof configurations—a roofspace with insulation laid at ceiling level with a reflective R1.3 roof blanket, against a cavity batten system with a Class 4 Vapour Permeable Membrane—with varying levels of roofspace ventilation, and their impact on the star rating of the home.

Adding a reflective R1.3 roof blanket has been standard practice but as homes get more energy efficient and airtight, having a reflective foil anywhere in the wall or roof is a source of risk for condensation and moisture.

It’s understandable that architects feel anxiety around changing systems, details, construction methodologies and specifications, but in this experiment, I’m going to show that changing the system to one that is more durable, resilient, and healthy for the occupants doesn’t necessarily lead to a significant impact on the star rating performance.

The Findings

The findings are quite interesting. We see that as we introduce some form of roofspace ventilation underneath a reflective roof blanket, we lose performance. Conversely, when we introduce some form of roofspace ventilation underneath the vapour permeable membrane, we gain performance.

This finding is expected, a reflective foil works best when it faces a cavity that is still and has little to no air movement. Whereas within a vapour permeable membrane cavity, we want to facilitate air movement through the cavity to introduce drainage and drying.

These findings underline the fundamental difference between these systems, and where moisture and condensation moves from inside of the home to the outside, i.e., anywhere in Climate Zones 5, 6, 7, and 8, we want to be able to let the moisture move through the membrane, condensate on the outside of the membrane and structure, and then drain away and dry. The more we hinder this process, the higher the risk of condensation forming on the insides of the structure.

A reflective foil acts against this process and thus increases the condensation and moisture risks, negatively impacting long-term resilience, performance, and occupant health.

It’s worth noting that we do see a minor drop in star rating performance when we switch out the reflective blanket for a vapour permeable membrane, which is why they’ve been popular during the 6-Star regime, as it was an easy implementation to achieve compliance targets. But what we can see is that this performance gap is made much smaller by upgrading the insulation we’re using at the ceiling level.

What can you implement today?

What’s great is that we don’t have to reinvent the wheel. There are proven systems available in the market that work and enable you to deliver healthy, comfortable, and resilient homes for your clients.

But what can you do today that will make a difference?

Maximise the ceiling level insulation
Ensure the ceiling insulation thickness is kept constant towards the edges of the roof; if needed, consider heeled-trusses to get the insulation in
Introduce ventilated cavities to your walls and roofs; remember, the best wall is a roof, and the best roof is a wall
Investigate roof ventilation systems beyond the whirly bird. These are old pieces of technology and prone to failure… How many do you see that have stopped spinning?! Refer to the Resources and Additional Reading section at the end of this article for other roof ventilation systems
Optimise the home early and understand where the balance of cost and benefit lies; leaving energy efficiency until the end leaves you needing to implement systems instead of choosing what works best for the project

The Subject of the Experiment

To help set the context for this experiment, the project used for these investigations is a 2-storey home orientated on a long and skinny block with the front door facing east and the Kitchen and Living facing west. The ground floor ceiling and roof structure is a gable roof, with the upper floor being a low pitched hip roof.

The project is situated within ABCB Climate Zone 5 and NatHERS Climate Zone 16, and was certified at the compliance requirement of 7-Stars.

It’s worth noting that as we move this project into colder climates, it will naturally lose star rating performance as a result. This article is to simply outline the performance differences in the change in roof level configuration and ventilation—not to dive into the intricacies of climate-responsive design.

In our investigations, the project starts off with:

R5.0 ceiling insulation
A reflective R1.3 roof blanket
Minimal ventilation occuring throughout the roofspace

For the alternative roof configuration, the setup is as follows:

R5.0 ceiling insulation
A Class 4 Vapour Permeable Membrane with a 20mm non-reflective airgap above membrane, and a ~90mm non-reflective airgap below the membrane
Minimal ventilation occuring throughout the roofspace

The Results

Note: We are comparing the home’s total energy loads per m2, a lower number is better.

Note: X-axis explanation:

Min. ventilation: attic roofspace with minimal roofspace ventilation, e.g., no dedicated roofspace ventilation system
Nat. ventilation: Naturally ventilated attic roofspace, e.g., eave vents & whirly ventilator/ridge cap vents
Mech. ventilation: Mechanically ventilated attic roofspace, e.g., eave vents & powered roof ventilator

**Graph 1:** ABCB Climate Zone 5 & NatHERS Climate Zone 16

**Graph 2:** ABCB Climate Zone 6 & NatHERS Climate Zone 21

**Graph 3:** ABCB Climate Zone 7 & NatHERS Climate Zone 60

NatHERS Limitations

While the team behind HERO have done a tremendous job at implementing future-ready performance modelling solutions, it’s worth noting some HERO and NatHERS limitations as of the time of writing.

Roofspaces within HERO are unique and have a few options and customisations, you can understand more about what can be assessed here: HERO Roofspace Zones
- For example, roof level ventilation in HERO has 3 distinct toggles as we have shown in the experiments above: minimal, natural, and mechanical
There is currently no ability to add a level of ventilation to flat-framed roofs within NatHERS
HERO has a number of preset options when it comes to ceiling and roof level insulation, you can check out what is available here: HERO Ceilings & Roof Insulation
HERO allows you to customise wall construction, but does not allow you to create custom roof and floor assemblies, these are preset but will be customisable in future versions

Resources and Additional Reading

The Architect's Guide to Energy Efficiency: The Hidden Impact of Roof Ventilation on NatHERS