Why Passive House Performs – A Sub-Tropic Tale

Hydraulic engineer Gabrielle Dennis had been living in uncomfortable homes for years in Sydney and elsewhere. Homes that were hard to cool in summer, too cold in winter and often prone to mould. So when she started planning her forever home in northern NSW, designing a home that had low energy costs, was comfortable all year round and would not get damp was a major priority.

“I knew from experience how well houses in Europe worked,” she says. By comparison, the standard of many Australian homes is inferior.

Gabrielle researched a range of building styles to examine their performance in terms of comfort and corresponding energy costs including brick veneer, weatherboard and reverse brick veneer before discovering Passive House.

“It seemed like Passive House had solved the problems.” Having a standard to work to also meant a designer and builder would not need to “reinvent the wheel, because they have the recipe.”

Gabrielle approached Architect Kylie Mills from BluKube Architecture with a home design originally drafted by Gabrielle’s father, himself an architect, and asked Kylie to turn it into a Passive House plan. She had also purchased a block in Ballina, Northern NSW to build the home on.

The redesign involved a brief for a three bedroom plus media room, two bathroom plus ensuite dwelling with garage. There is a large living area with high ceilings that opens out to a deck. The design incorporates features for ageing in place including wheelchair-friendly layout, step-free entries, wider doorways and a guest wing so Gabrielle can have a house flatmate or a carer as life changes. The garage has solar photovolatic panels on the roof and is EV-charging ready.

Northeastern downpipes

It is believed to be the first home in the Ballina local government area designed and delivered in alignment with Passive House standards. Gabrielle says that meant there was no established builder with prior experience, so a custom builder had to be contracted.

For Kylie, the home was her first opportunity to design and be project architect on a sub-tropical zone dwelling that would aim to be a certified Passive House. “The journey has been really interesting,” she says.

Because they had no prior knowledge of any builders in the region who might be up to the job, a dozen builders were approached to submit an Expression of Interest in the project. Kylie and Gabrielle met with four of the builders.

Looking back Kylie says this was something of a “surreal experience.”

“We were in the carpark of the Big Prawn at Ballina after the builders’ meetings when we received a message from builders Stewart and Cameron Scholten from Scholten Group, saying they had just enrolled in the Passive House tradesperson course.

“I said to Gabrielle, I think we may have found our builder.”

Together, architect, client, builder and the trades all “went on a journey” to discover how to make Passive House work in the climate zone and for the specific home Kylie had designed for Gabrielle. “A warm climate Passive House is different from the conventional Passive House many are familiar with being built in Victoria,” Kylie says. The hands-on learning process involved everyone on the project. The structural engineering consultant for example included three large steel beam structures and columns in their design, and Kylie explained to them that these were thermal bridges and options for changing them out for timber were needed instead.

“There are all these interesting details in Passive House designs that you don’t really see,” Kylie says. That includes needing to add extra insulation everywhere, including the slab edge. Both Gabrielle and Kylie became adept reading the thermographic camera images to verify insulation, and it was thermographic imaging that clinched the case for slab edge insulation. It was clearly a weak point, as it is one of the final elements to be installed for Passive House requirements.

Thermal break with fiberglass insulation elements at steel columns

Another fundamental element of Passive House is ensuring a healthy home with excellent ventilation. A heat recovery ventilation system was installed at the Ballina home that will ensure a steady flow of filtered fresh air at optimum comfort temperature flows into the house. Part of the detailing was ensuring the unit is located at a height that allows Gabrielle to safely and easily change the filters every year.

HRV filters easy to reach for annual replacement as part of building maintenance 

Other elements of the build that required tradies to take additional care included ensuring every penetration was sealed properly, and that holes in the air-tight weatherproof membrane used to wrap the whole home were fixed promptly so no moisture could get inside the wall assemblies.

“It was ongoing learning for everybody,” Kylie says. “The final product selected for this was an adhesive membrane. Installed like covering a book with contact, though at a much larger scale.”

Some suppliers proved to be a tremendous source of knowledge, and so did many of the tradies. Kylie says that for some of them, the process of Passive House construction and detailing such as taping joints of the building wrapping are a return to the fundamental skills taught when they began their apprenticeships.

Being onsite regularly as the homeowner Gabrielle was often joined by Kylie thanks to digital technology, to explain to the builder what needed to be achieved and why it mattered in terms of Passive House building performance. At times this resulted in the tradies and builder suggesting an alternative method to achieve the same result that may be simpler to build.

Kylie says that having rapport with the trades is essential, as every single trade needs to know what they are doing because their work affects the final performance of the building.

The saying “oh but we’ve always done it this way,” has to be removed from the lexicon, Kylie says. Toolbox talks are also important to ensure everyone understands what needs to be done and how it needs to be done.

Kitchen

There is a bigger picture dimension also, of explaining to the trades that high performance homes are the future direction of the industry. This project has given those involved the skills to lead the charge in the area.

After each trade whose work affected the exterior envelope had completed their work, such as the electrician installing the hot water system and wiring for external lighting, the builder would do a full inspection to ensure all penetrations were sealed.

Quality is a fundamental part of the equation. Many of the features of detailing of a Passive House such as ensuring windows are installed and sealed correctly are fundamental to quality workmanship. With this kind of project, the blower door testing used to verify air sealing meets the standards for Passive House certification will also reveal if the installation hasn’t quite been up to scratch.

Part of the contract with the builder working on Gabrielle’s house specified that blower door testing would be used to check the quality of work, as well as photographic verification expected for the insulation installation to meet Passive House Classic criteria for certification.

Gabrielle says she can’t imagine not having the design and building the house she now has.

Shading hoods on western and northern facades

She was hands-on with the process, onsite most weekends and taking on many of the “tedious” tasks like wrapping water pipes inside the walls with insulation so they would not become a cause of condensation. In Ballina the climate features humidity and heavy dew, and the kind of plumbing products that reduce condensation risks as a result simply are not available on the market yet.

Other fine details include pre-planning and installing blocks in the walls for the easy installation of grab rails, picture rails – even the toilet roll holders. This removes any chance affixing them in future might penetrate the insulation or building membrane.

“My Dad was an architect, so I pretty much grew up on a building site,” Gabrielle says. “I set out with this house to prove Passive House works for hot climates. The same heat transfer equations still apply.

“I do envisage my home being used as an example of the way of the future. We do need to change the way people build.”