7 Star Homes: How Window Size Impacts NatHERS Ratings

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7 star homes are now the minimum energy efficiency standard for most new residential buildings in Australia under the National Construction Code (NCC). These homes are assessed using the Nationwide House Energy Rating Scheme (NatHERS), which measures how well a dwelling maintains a comfortable internal temperature with minimal reliance on heating and cooling. 

While insulation, orientation, and materials all contribute to a home’s energy rating, window size and placement consistently have one of the biggest impacts on whether a design reaches 7 stars. As NatHERS energy assessors, we regularly see well‑intentioned designs struggle to pass because of oversized or poorly located glazing.

This article explains how window size affects thermal performance, why larger windows can reduce NatHERS ratings, and how smart window design can help achieve compliant, comfortable 7 star homes—without sacrificing daylight or views.

What Makes a 7 Star Home?

NatHERS rates homes on a scale from 0 to 10 stars, based on the amount of energy required to keep the home comfortable year‑round. A 7‑star rating represents the current minimum standard under NCC 2022 and reflects significantly improved thermal performance compared to earlier standards.

A 7‑star home:

• Requires less heating and cooling energy
• Maintains more stable indoor temperatures
• Relies more on passive design than mechanical systems

NatHERS assessments focus on the building shell, including walls, roofs, floors, and—most importantly—windows. 

Why Window Size Matters in 7 Star Homes

Windows play a disproportionate role in thermal performance. Independent industry research shows that a large proportion of heat loss and heat gain in Australian homes occurs through glazing. 

From a NatHERS modelling perspective, window size affects:

• How much heat enters the home in summer
• How much heat escapes in winter
• Internal temperature stability across daily and seasonal cycles

Even high‑quality glazing can negatively affect a home’s rating if window area is excessive or poorly oriented.

The Trade‑Off Between Views and Energy Performance

Modern residential design often prioritises large windows to capture views and natural light. However, in the context of 7 star homes, bigger windows do not automatically mean better outcomes.

Common issues we see in NatHERS assessments include:

• Large west‑facing windows that increase cooling loads
• Excessive window‑to‑floor area ratios
• Glazing placed without effective shading

In NatHERS software, these factors can quickly increase predicted heating and cooling loads, pulling the overall star rating below 7—even when insulation and materials are otherwise compliant. 

Common Window Design Mistakes That Prevent 7 Star Compliance

Oversized Glazing in High‑Exposure Orientations

Large areas of glazing on western or eastern façades often create overheating issues that are difficult to offset later.

Overcapitalising On Floor To Ceiling Windows

Outdoor living spaces are prime candidates for generous glazing—but even here, proportion matters when looking at the window. Some things to consider are:

• The top 300mm sees roof: Floor-to-ceiling glass may include a strip of roofline that adds no visual benefit.
• The bottom 300mm sees floor: Similarly, the lowest section often reveals paving or decking, not the garden or landscape.
• The sweet spot: The most engaging views are typically between 300mm and 2100mm above floor level—where people’s eyes naturally rest.

Assuming Better Glass Fixes Everything

While double glazing and Low‑E coatings help, glass performance alone rarely compensates for poor sizing or placement.

Late Design Changes

Increasing window sizes late in the design process frequently causes previously compliant homes to fail the 7‑star threshold.

How to Balance Views, Daylight, and 7 Star Performance

Achieving 7 star homes does not require eliminating views or daylight—it requires balanced design choices. Effective strategies include:

• Prioritising glazing to north‑facing living areas
• Limiting glazing on west‑facing façades
• Using targeted window placement instead of large continuous panels
• Incorporating appropriate shading devices
• Engaging a NatHERS assessor early in the design phase 

Early thermal modelling allows designers to test window sizes and configurations before plans are locked in, avoiding costly revisions later.

A NatHERS Assessor’s Perspective on 7 Star Homes

From a NatHERS assessor’s perspective, window design is one of the most influential—and most underestimated—elements in achieving 7 stars. Designs that struggle to pass rarely fail because of a single issue, but excessive glazing is one of the most consistent red flags we encounter.

By addressing window size, placement, and shading early, many homes can achieve a compliant 7‑star rating with fewer upgrades elsewhere in the building fabric.

Final Thoughts

With 7‑star energy efficiency now the baseline standard, achieving compliance is no longer optional—it is fundamental to residential design. Window size plays a critical role in determining thermal performance and NatHERS outcomes, particularly in today’s view‑driven architectural styles.

Thoughtful window design—guided by early energy assessment—allows homeowners and designers to deliver comfortable, efficient 7 star homes without compromising liveability or aesthetics.

Need to achieve a 7 star home?

At Assessify, we specialise in fast, accurate & collaborative NatHERS Certificates. Whether you are an architect, builder, or owner-builder, we help you navigate the 7-star requirements with ease. Check out our NatHERS page for pricing and to organise your quote.