What is a Passive House?

Over the last decade, energy efficiency has become a key consideration in many more new home designs. Whether this is for environmental or economic reasons – or both – it generally requires the challenging of traditional building techniques. And fewer movements are a better example of this than the rise in popularity of Passive House designs.

Here we take a closer look at where this movement has come from and what it stands for. As part of this, we will explore the principles of Passive House design and why homeowners are increasingly adopting them. We will also consider what a modern home design looks like when adhering to the Passive House principles.

History of the Passive House

While the Passive House (or Passivhaus) Standard has roots reaching back as far as the 1970s, the modern incarnation is much younger. In fact, a block of four townhouses in Darmstadt, Germany, is considered the first true example of Passive House design. Completed in 1991 for private residents, this modest structure is credited as the first to meet the required efficiency standards.

Following this, Darmstadt quickly became the home of Passive House design, with the Passivhaus-Institut founded in the city in 1996. Initially set up to administer the Standard, the Institute has played a key role in promoting the Passive House approach. This led to the development of specialised components, most notably windows and ventilation systems, designed to meet the Standard’s requirements.

Although most Passive House developments were initially located in Germany and Austria, the movement has since spread worldwide. This includes Australia, where there is now a dedicated Australian Passive House Association and over 90 certified designers and tradespeople. And while there were only 40 certified Passive Houses in Australia at the start of 2022, this number is rapidly increasing. There have also been many more projects which have adopted Passive House principles but have not sought certification.

Features of a Passive House

While Passive House designs vary greatly, they all share a few critical characteristics. These are set out in the Passive House Standard, which acts as a guide for all new Passive House designs. It is also the criteria all structures seeking Passive House certification are measured against.

The Passive House Standard sets out six key requirements:

1. Energy required for heating: Passive homes must require less than 15kWh/m2 per year, or 10W/m2 at peak times, to heat. By comparison, the average standard home requires around 100 W/m2 of heating energy at peak times.

2. Energy required for cooling: Passive homes must also require less than 15kWh/m2 per year, or 10W/m2 at peak times, to cool. In more tropical climates, this allowance is increased slightly to account for dehumidification.

3. Thermal comfort: Passive homes must maintain a stable climate year round, with the internal temperature not dropping below 20oC. The internal temperature must also stay below 25oC for at least 90% of the time in any given year. In extreme climates, these allowances can be adjusted slightly to account for average temperatures.

4. Humidity levels: Passive homes must maintain a humidity level of below 12g/kg for at least 80% of the time in any given year. This equates to a maximum approximate relative humidity level of 60% at 25oC.

5. Level of airtightness: Passive homes must have less than 0.6 air changes per hour at a pressure of no more than 50 pascals. This is critical to preventing heat loss (and gain) and must be measured on-site for certification. Passive Houses also require a mechanical ventilation system with heat recovery to maintain the supply of fresh air.

6. Total energy consumption: Passive homes must maintain an overall energy consumption of less than 60kWh/m2 per year. This is a holistic measure that includes all building procedures (heating, cooling, hot water, lighting, etc.) and occupant energy consumption.

To achieve the required level of efficiency, there are five principles every Passive House design needs to adhere to:

1. Minimal thermal bridging: A thermal bridge is a weak spot in the insulation of an internal space, which could cause heat losses. As they can impact the temperature of the surrounding area, these spots must be identified and extra thermal protection added. Common thermal bridges include windows, doors, ceiling junctions, corners, balconies, and eaves.

2. Superior insulation: Insulation has long been used to help maintain the internal temperature of a property. Passive Houses take this to the next level, using higher quality products and ensuring consistent application throughout the structure. An experienced custom home builder should be able to recommend a suitable high-performance insulation product for your Passive House project.

3. Specialised windows: Windows are arguably the biggest thermal bridges in most homes, allowing for significant amounts of heat energy to be lost. This is particularly true here in Australia, where thin single-glazed windows are common. To address this, higher quality thermally broken double-glazed windows are generally used in Passive House designs. Double-glazed windows are a standard feature of all Carmel Homes knockdown and rebuild projects.

4. Airtight construction: As stated in the Standard, airflow in to and out of the internal spaces should be tightly controlled. To help achieve this, a range of specialised products and techniques have been developed and are now available. That said, ensuring airtightness still needs to be a key focus at both the design and build stages.

5. Great ventilation: A high-quality ventilation system is required to manage and control the flow of air between internal and external spaces. This must include a heat recovery mechanism that extracts heat from the exiting air and transfers it to the incoming air. It should also feature a high-performance filtration system to help maintain the quality and health of the indoor air.

Benefits of a passive house

The biggest and most obvious benefit of Passive House designs is how energy efficient they are. According to some studies, heating and cooling in a passive home require up to 90% less energy than in a standard home. This, in turn, creates a range of other benefits, including:

• Significantly lower running costs: Because they are so energy efficient, passive homes require much less power than the standard home. This means much lower utility bills, which is especially beneficial in the face of rising electricity and gas prices.

• More comfortable: Because the internal temperature is so stable, there are no hot or cold spots throughout a passive home. Also, as most of the heat comes from natural sources (solar heat, occupant body heat, etc.), it feels much less stuffy.

• Better air quality: As great ventilation is a key design principle, passive homes enjoy a constant supply of fresh, filtered air. This helps manage odours and pollutants and improves the overall health of the home environment without creating any unpleasant draughts.

• Quieter: Due to the higher quality insulation, airtight sealing, and specialist windows, passive homes also experience less noise pollution. Passive Home principles can also help increase soundproofing in high-density and multi-occupancy developments (townhouse developments, apartment complexes, etc.).

• More resilient: As they are not reliant on heating or cooling systems, passive homes are not really affected by power outages. Even in the depths of winter or the height of summer, they will remain habitable much longer than a standard home.

Considerations when building a Passive House

In addition to the key design principles, several other factors need to be carefully thought through when planning a Passive Home. This includes the:

• Style of the home: Among existing Passive Houses, French Provincial homes are quite rare, but more modern home designs are far more common. This is because Passive House principles and features more readily lend themselves to more modern home designs. However, an experienced design and build specialist should be able to adapt them to suit more traditional styles, like French Provincial homes.

• Certification v Inspiration: To help promote excellence in Passive House design, homes strictly adhering to the standards can apply for certification. This allows them to be listed as Passive Houses and included on databases of the country’s most energy-efficient properties. However, you may just choose to adopt certain elements of the Standard and not seek certification. This should still deliver many of the same benefits while allowing you greater flexibility in your design.

• Starting from scratch: Creating a truly Passive House requires a holistic approach, with careful consideration given to each element of the design. As such, these principles are best suited to new build and knockdown and rebuild projects. However, if you would prefer not to knockdown and rebuild, it is possible to retrofit Passive House components to existing properties.

• Extraction fans: One of the unique challenges a Passive House presents is the complications it creates around using kitchen rangehoods, etc. As internal spaces are essentially airtight, removing air (as an extractor does) creates negative pressure. Avoid this by installing either an airtight valve or a system that filters and recirculates the extracted air.

Want to discuss this further?

If you are considering building a Passive House, or want to include passive principles in your new home design, contact Carmel homes. In addition to being one of Melbourne’s leading luxury custom home builders, we are deeply committed to sustainability. As such, we can help you develop a design that looks beautiful, suits your lifestyle, and is highly energy efficient.