Passive House vs 9-star NatHERS: what actually delivers comfort

NatHERS (Nationwide House Energy Rating Scheme) is a predictive rating. A NatHERS assessor uses simulation software to model the energy consumption of the home under standard occupancy assumptions, standard climate data and standard performance inputs. The result is a star rating from 0 to 10.

Certified Passive House is a measured performance standard. The design is modelled in PHPP (the Passive House Planning Package) at concept stage, but the certified outcome depends on measured verification: blower door test for airtightness, calculated heating and cooling demand, and observed performance in occupation.

The practical difference is significant. A NatHERS-rated home might achieve 9-star on paper but perform worse in practice if construction quality does not match the modelling assumptions. A Passivhaus home has been physically tested; the number is real.

NatHERS is primarily an efficiency standard. The star rating reflects predicted energy consumption. A high-star NatHERS home uses less energy, but the standard does not specifically address the quality of the internal thermal environment.

Passivhaus is primarily a comfort standard. The design targets: internal temperature within a narrow comfort band year-round without active heating or cooling, low internal humidity variation, no draughts, and quiet mechanical systems. Energy savings are a consequence of the design, not the primary goal.

For an Adelaide family, the practical difference is felt in mid-winter and mid-summer. A NatHERS 9-star home in Adelaide will typically be a few degrees below comfortable in mid-winter without active heating, and require active cooling for the hottest weeks in January and February. A well-designed Passivhaus will typically hold within one to two degrees of comfortable year-round with minimal active intervention.

NatHERS assessment costs a modest fee. It is required for all new homes in South Australia under the National Construction Code 2025 as part of the building consent process. The certificate is issued by an accredited NatHERS assessor.

Certified Passive House requires: PHPP modelling by a Passivhaus designer, verification by a Passivhaus certifier, blower door testing, and submission to the Passive House Institute in Germany (or an approved intermediary). Certification fees typically run in the low tens of thousands of dollars all in.

For homeowners who value the third-party validation of Passivhaus, this is a modest cost relative to the build. For homeowners who simply want a low-energy home without formal certification, following Passivhaus principles without pursuing certification (sometimes called "Passivhaus-inspired") delivers most of the comfort benefit at a fraction of the certification cost.

The build cost uplift for certified Passivhaus over NatHERS 7-star is typically 10 to 20 percent of the total build cost, depending on how well the design is optimised. The uplift over NatHERS 9-star is smaller, typically 5 to 12 percent, because both standards demand strong envelope performance.

The cost drivers of the Passivhaus uplift are: higher-performance windows (double or triple glazed with insulated frames), continuous insulation to reduce thermal bridges, mechanical ventilation with heat recovery, and specialist detailing of the airtight layer.

The cost is offset over time by lower running costs (electricity for heating and cooling is a fraction of a conventional home) and by resale premium in some Adelaide markets. It is rarely a financial-first decision; it is a comfort-first decision with financial upside.

For most Adelaide families in 2026, the practical choice is between NatHERS 7 to 8 star (the compliance baseline plus a modest uplift), NatHERS 9 star (a significant step up in efficiency), and certified Passivhaus (a significant step up in comfort with a further cost premium).

Choose NatHERS 7 to 8 star if you want a code-compliant, energy-efficient home at close to conventional cost. This is the mainstream choice for most Adelaide new builds and delivers a genuinely more efficient home than the 6-star homes of a decade ago.

Choose NatHERS 9 star if energy efficiency is important to you but formal certification and the highest tier of comfort are not. This delivers 60 to 80 percent of the Passivhaus outcomes at a fraction of the certification and detailing effort.

Choose certified Passivhaus if you want the highest tier of comfort and health, are prepared to accept the cost premium, and value the third-party verification of the outcome. This is the choice for owners who plan to live in the home for a decade or more and for whom internal air quality is a health issue, not a nice-to-have.

There is no wrong choice. All three are significant improvements over the pre-2025 building code baseline. The right choice depends on your priorities and your budget.