For almost three decades, Umow Lai has been engineering sustainable environments, and we are proud to have two of our sustainability consultants recently complete the Passive House Designer Course. David Arnott and Tom Hubbard are now Certified Passive House Designers; we caught up with them to discuss what Passive House Design is, and how it benefits buildings and their occupants.

What is Passive House?

Passive House is a building standard which embraces five design principles to achieve a set of strict performance criteria. It utilises building physics, combined with carefully considered building services to provide healthy, comfortable and quiet indoor environments at a very low energy cost. Despite the name Passive House, it is not just for residential buildings and certification has been successfully realised in offices, hospitals, schools and hotels. With an undeniable track record of success worldwide, Passive House is gaining momentum with Australian building owners for the multitude of benefits inherent to any and all Passive House buildings.

Passive House employs five key design principles to accomplish robust and quantifiable performance criteria for energy efficiency and comfort levels. The five design principles are as follows:

  1. Thermal insulation
  2. High-performance glazing
  3. Thermal bridge free construction
  4. Airtightness
  5. Mechanical Ventilation Heat Recovery

These Passive House fundamentals are assessed throughout the design process using the Passive House Planning Package (PHPP) along with supporting software packages and physical testing – such as blower door testing. Ultimately to achieve certification, the final PHPP and supporting evidence needs to be verified by a Passive House Certifier to confirm the design is meeting all performance criteria. The performance criteria are:

  • Annual primary energy demand, set at = 120kWh/m²a.
    Alternatively, with renewables, it is set at = 60kWh/m²a. This is the predicted total energy demand of the building.
  • Annual space heating demand, set at = 15kWh/m²a.
    Alternatively, the space heating load is set at 10W/m².
  • Annual space cooling/dehumidification demand, which is set at = 15kWh/m²a. Alternatively, the space cooling load is set at 10W/m².
  • Airtightness, which is set at = 0.6 ACH (measured at 50 Pascals). For larger buildings, air permeability is set at = 0.6m³/hr.m² (measured at 50 Pascals).
  • The indoor humidity levels do not exceed 12 g/kg for more than 20% of the occupied time.
  • The air temperature must not exceed 25°C for more than 10% of the occupied time.

Why should owners invest in Passive House Design and Certification?

David: There are many benefits to building a Passive House project. The energy efficiency benefits assist in reducing running costs by 75-90%. There are also health and comfort benefits inherent in any Passive House. The provision of continuous, superior quality fresh air improves the internal environment, while also removing unwanted odours and pollutants. While thermal bridge free construction ensures there are no cold spots, which works with the supply air to eliminate the opportunity for mould growth.

Due to their detailed and somewhat bespoke nature, a Passive House building is going to be more thoroughly considered, detailed and constructed than a comparable standard build, with a higher likelihood that the result will be of better quality.

Tom: There is a level of certainty provided by Passive House buildings. The standard is backed by years of research, there are case studies which prove the success of Passive Houses (the first Passive House was constructed in 1991 and still performs and this performance is calculated based on the fundamentals of physics. This provides assurance which can turn into marketability – potential buyers or tenants can be confident they will be getting an efficient, comfortable and well-built building and therefore should be willing to pay more.

The Passive House standard also delivers a highly resilient building. The comfort and health benefits are effectively “designed in” so that they are provided for the majority of the time. These buildings do not need to “react” too hot/cold temps; they are simply always working.

What are the benefits of Passive House in commercial spaces?

David: Improved internal environments have been shown to lead to increases in staff well-being and productivity. These spaces also benefit from low operational energy demand, meaning low operational costs. For mechanical services, due to Passive House’s fabric first approach, designs can be simplified, whereby complicated systems and controls are no longer required to deliver efficiency.

Tom: The benefits for commercial Passive House spaces are the same as any other type of Passive House project and these benefits have been verified by varied studies on completed projects. Day-to-day benefits include:

  • comfortable temperatures
  • high level of building sealing means no drafts, no dust and no spiders
  • ventilation allowing for fresh air all the time
  • the insulation helps reduce noise
  • up to 90% reduction of heating energy compared to a standard build

Is Passive House Certification hard to achieve?

David: If you have a project team – including the builder – who understand the process and who commit to the level of detail and diligence required, achieving certification should be relatively easy. The potential difficulties arise when this level of effort is underestimated, which highlights the importance of engaging experienced and conscientious teams.

Can you retrofit existing buildings to a passive house standard?

Tom: You can, and there is a specific standard for this purpose. It’s called “EnerPHit” and has the same principles, however, has some minor differences in the requirements to account for it not always be possible to mitigate all the thermal bridges.

David: There are inherent boundaries on an existing building that may limit you to achieve the strict Passive House performance criteria when refurbishing a building, regardless of how much money you have to spend. However, this is recognised by the Passive House Institute with the EnerPHit standard. This standard works to the same five design principles, that when implemented correctly, can achieve enormous gains in thermal performance, energy efficiency and comfort.

What are resale benefits of Passive House buildings?

David: It’s difficult to say with any certainty how the Australian market will react to increased Passive House buildings, given there are currently very few completed projects. I would suspect that in the years to come – particularly in the commercial office sector – a Passive House building will be sort after for the benefits it provides in energy efficiency, health and improved indoor environment quality. It’s not a stretch to imagine that this will start to drive the market in the same way that a higher NABERS rating has now started to impact sales prices and the available yields owners can expect. I imagine the superior build quality of a Passive House building will also have a market impact in the mid to long term.

Tom: The certification adds value and the performance that comes with it is noticeable. There is a level of certainty in performance with certified buildings which standard builds just cannot guarantee. And this performance is really quite tangible, we notice comfort within our buildings and we can quantify how much it costs to run them. I wouldn’t be surprised if soon building owners, who proactively design with Passive House in mind, will be able to charge more because people will be willing to pay a premium for Passive House buildings.

Is there any benefit to building to a Passive House standard in warm climates?

David: There is a common misconception that Passive House is only suitable for cold climates; this is wrong. The laws of building physics are the same regardless of location, and there are only a very small number of locations, with extreme climates (think Antarctica) where a Passive House building cannot work. While different climate zones will present different challenges (such as humidity), they can all be easily overcome with a well-considered design approach.

Tom: The Passive House Standard was intended to be independent of climate, to be far-reaching and work anywhere. Right here in Melbourne, there was an Icebox challenge which directly compared the performance of a standard practice BCA build and a Passive House build. The demonstration happened this year (2019) and was over some of the hottest days in February. This experiment highlighted the stark difference between the building code and the Passive House requirements. There is much room for improvement!

What are the steps to becoming a Certified Passive House Designer?

Tom: There is a two-week intensive course and then a final exam which is sent back to Germany for official marking. For those who are interested, there is even a certification for tradespeople, which covers how to build to the Passive House Standard. There is a limited number of tradespeople in Australia with this certification (about 50) so it would be beneficial to have more people with this knowledge that could be implemented during construction.

David: Aside from the course and the exam, to become a Certified Passive House Designer you must have a tertiary qualification in engineering, architecture or a related field (otherwise you become a Certified Passive House Consultant). To give yourself the best possible chance at passing – and then successfully implementing the principles into the design – it’s recommended that you have a working knowledge of construction detailing, mechanical design and simple building physics. Although it isn’t relevant to consulting engineers, a Certified Passive House Tradesperson qualification is available and is highly recommended when appointing a builder on a Passive House project.

If you are interested in learning more about Umow Lai’s Sustainability and Passive House teams, please get in touch with us to see how your project could benefit.

Pictured above: Klinikum Frankfurt Hoechst, the first hospital in the world to be built to a Passive House standard visited by Umow Lai’s Principal Sustainability Consultant on his recent global study tour.