What is Passivhaus House Design in Architecture?

The Passivhaus design standard for homes and buildings has become a growing interest for many aspiring homeowners looking to build an energy-efficient home in Australia. As of 2024, the Australian Passivhaus Association (APA) has issued Passivhaus certification for over 70 buildings across Australia, and there are reportedly hundreds of buildings that are working through the certification process. 

An energy-efficient home is certainly ideal for many homeowners — think lower energy bills, a more comfortable living space, and better thermal insulation. There are also long-term benefits, such as a healthier environment for the family, especially for kids and the elderly who are more sensitive to respiratory and skin health conditions that are triggered in traditional homes.

So, what is ‘Passivhaus’ design, and what does it mean to build with passive design in mind?

What Does Passivhaus Mean?

Passivhaus, also known as passive house, is a design standard originating from Germany that focuses on optimising the thermal performance of a home. Passive house design involves creating a building that can maintain a comfortable temperature without requiring any mechanical heating or cooling. 

To achieve this, Passive House works on the principle of creating an airtight building that is optimally insulated to prevent the unnecessary transfer of heat to or from the interior. Buildings can only obtain Passive House certification when the design standards are met:

• Maximum and minimum internal temperatures of 25°C and 20°C, respectively, within the building. 
• Heating and cooling energy demand no greater than 15 kWh/m² each year. 
• Maximum internal humidity of 12g/kg for at least 80% during the year.
• Airtightness rating lower than 0.6 air changes per hour at 50 pascal. 
• Maximum renewable primary energy demand of 60kwh/m² per year.

The Principles of Passive House Design in Architecture

There are five main principles of passive house design — each of these principles addresses a part of the home to ensure optimal thermal performance. 

1. Building airtightness 

Openings in homes, such as windows and doors, are one of the biggest areas of heat transfer. In Passive House design, these openings are constructed to have as little air leakage as possible when closed. With a complete seal on all openings, the home can maintain a comfortable temperature to prevent cold or warm air inside from escaping. This doesn’t mean that the inside of the home will become stuffy — there can be plenty of ventilation when the windows and doors are left open. 

2. Thermal insulation

Thermal insulation in a Passive House is achieved by constructing its external envelope with high-quality insulation materials. The external envelope of the home includes structural elements such as walls, ceilings, and the floor. Similar to airtightness, thermal insulation is installed without any gaps or bulges to maintain a stable, comfortable indoor temperature. 

3. Window glazing

Windows allow solar radiation to naturally enter and warm the interior of a home, but are also vulnerable areas for heat loss. For this reason, double or triple-window glazing is used as part of Passive House design. In most regions of Australia, double glazing is usually sufficient to achieve the Passive House standard for thermal efficiency.

4. Ventilation with heat recovery

Mechanical Ventilation with Heat Recovery (MVHR) systems are implemented in a Passive House to provide continuous fresh air while minimising energy loss in the airtight environment. In addition to providing consistent air quality in the house, mechanical ventilation also works to cycle warm or cool air back into the building and regulate the internal humidity. 

5. Minimising thermal bridges 

Thermal bridges refer to parts of the building that have a high potential for heat transfer. Windows, doors, and openings to a balcony or outdoor space are examples of thermal bridges. Even a small amount of heat transfer can significantly impact the thermal performance of the home, which is why Passive House architects work to reduce thermal bridges in the home by using low-conductive materials where possible.

How Do Passive House Standards Compare With NatHERS?

The Nationwide House Energy Rating Scheme (NatHERS) is the standard for measuring the energy performance of Australian homes. According to updates from the 2022 National Construction Code, all new Australian dwellings must meet the requirement of a minimum 7-star NatHERS rating. So, how does Passive House design compare with this requirement?

While the outcome does include improving the energy efficiency of the home, Passive House design is not solely focused on reducing the energy usage of the home. As a result, it’s not possible to equate Passive House design to a specific NatHERS star rating. 

However, Passive House design standards are considered to be stricter than the NatHERS measure of energy efficiency since it takes into account more factors such as thermal mass and airtightness. 

Applying Passivhaus Design

If you’re interested in building a Passivhaus home, it’s important to work with an architect who understands how to meet the standards of Passivhaus and the NatHERS. Aside from new homes, Passivhaus design can be applied to existing buildings to improve the building’s insulation, airtightness, and thermal performance — this is known as a Passive House retrofit. 

Passivhaus retrofit projects are ideal for heritage and older-built homes that often have poor thermal efficiency, greatly enhancing the natural level of comfort without the hassle of a full rebuild and allowing them to obtain Passivehaus certification. 

While the costs of a Passivhaus investment are not insignificant, the total energy savings gained over an average period of 4-7 years practically cover the same amount, making the investment well worth its cost in the long run.

As specialists in Passivhaus design in Sydney, Crush Architecture’s expertise extends to new home projects, renovations, and heritage home retrofits. We apply Passive House design to residential and commercial properties to achieve more naturally comfortable spaces that require significantly less energy for heating and cooling throughout the year.  Get in touch with our architects today to learn more about how we can help you create a Passive House.