Yes, Passive House Can Exist in the Sub-Tropics

Physics works in every climate – and so does Passive House

One topic guaranteed to generate passionate discussion among building designers is whether Passive House works for tropical and subtropical climates. The general perception is that as the approach was developed for cold climates where the biggest challenge is retaining warmth inside, cold climates are where Passive House should stay.

‘But what about mould?’ people say when they imagine a Passive House in a steamy rainforest.

‘What about passive cooling by opening the house up to the breeze?’

The word ‘esky’ may make an appearance.

The reality is the design and delivery of a Passive House building is based on physics, and like gravity, it works everywhere. The same principles of building science apply, as do the principles of managing thermal comfort and ensuring indoor air quality.

Examples Abound

Kylie Mills, principal of BluKube Architecture, says she has often been asked about Passive House in the tropical climates and how it might also work in the subtropics of Australia.

She notes that Certified Passive House buildings can be found in tropical climates in Salvador da Bahia, Mumbai, Singapore and Mexico and in subtropical places including Tokyo, Hyakuri and Shanghai.

“This demonstrates that certified Passive House can be achieved in all climates providing benefits for health and comfort,” Kylie says. It is also kind on the hip pocket in terms of running costs, no matter what climate zone it is in.

Breakthrough in Ballina

A recent project of Kylie’s in subtropical Ballina on the NSW North Coast is a good example. As Project Architect for the home being created for water engineer Gabrielle Dennis, Kylie worked closely with the client and the building team to deliver a Passive House outcome suited to the local conditions.

How They Did It

Gabrielle recognised the hardest element to control would be the humidity associated with the north coast climate.

“Insulation could take care of shielding the inside from the heat, but humidity is another story. I thought it would need a dehumidifier- and they are only viable for commercial buildings. Luckily a split system air conditioner in dry mode will do the job.

“The other complication with humidity is where the vapour barrier should be on the building, when the vapour drive here in the sub-tropics is the opposite to European experience- it would be from the outside to the inside.”

The Passive House WUFI building modelling tool calculations were used to establish where the vapour barrier would need to be.

Northeastern downpipes

Kylie says the home’s warm temperate environment meant the passive house planning package (PHPP) had to deal with the humidity and warmer months in the design, to prevent mould and overheating. In equipment terms, it was taken care of by including a 3.5KW air conditioning unit with dehumidification, located in the living room with draining condensate into the plumbing waste pipes.

Materials and Keeping Cool

Building Scientist at LAB Design, Madonna Stewart, is based in subtropical Woolgoolga. She and her Passive House Designer husband, Scott Stewart, have been applying the Passive House approach to projects in both northern NSW and southeast Queensland.

Madonna says the process of modelling is the same, as it is for homes in cold climates.

“It’s just the results and expectations are different,” she says.

While material choices are not markedly different in the warmer zones, some may have specific pros and cons that need to be considered, for example, some materials perform better from a moisture or thermal perspective.

“Glazing is one component which needs careful consideration in the warmer climates to ensure overheating remains within limits,” Madonna explains.

A balanced ventilation strategy is always used regardless of climate.

“In humid climates though, we may want to set the ventilation rate at the lowest allowable for a Passive House to reduce the amount of subsequent dehumidification required. An additional dehumidification system (or one combined with the ventilation system) is almost always required in the more humid areas.”

With a Passive House, when the weather is pleasant, it will make sense to open up the house as much as possible and take advantage of fresh air and natural ventilation. But even the subtropics don’t enjoy fabulous weather 24/7/365. Madonna notes that there “will be times when the outside conditions aren’t ideal; for example, it’s too hot, it’s too wet, it’s too dusty, too noisy and as such we want to shut our homes up and control the inside climate.”

“When the house is closed up, the ventilation and dehumidification systems need to work in unison to keep humidity levels at acceptable levels so as to not cause degradation of components. It’s also important to consider how to implement mechanical cooling systems without inducing condensation and hence ideal conditions for mould.”

Overheating in summer is often the biggest issue in warmer climates, she says.

“To avoid this, we need to find the right balance of insulation, glazing and shading to ensure the building can cool down sufficiently. Often homes can be over-specified in the warm climates which causes more problems due to the building not be able to cool down; things like triple glazing and under slab insulation are examples of over specifying.”

Shading hoods on western and northern facades

Double glazing that has the correct mix of Solar Heat Gain and U value is generally sufficient, and where a cold climate home might have heating through the slab, in the warmer zones Madonna says cooling through the slab is “usually beneficial”.

It is not only homes where Passive House is finding a niche in Australia’s subtropics. LAB Design are currently working on a ground-breaking commercial project on the Gold Coast that is taking the next step in terms of healthy buildings. “The Corner Block project is a totally new way to provide office and storage spaces,” Madonna says.

“Not only will the project be able to be certified under the Passive House Institute classifications, it incorporates revolutionary technologies such as UV cleansing overnight. It is a testament to the drive of our client that the project will be successful.”

Would you like to learn more about the in-construction Passive House in Ballina? Read more in our case study here.