Andy Marlow from Envirotecture explains why Passivhaus homes are a good fit for most climates in Australia, how they approach these projects and what is needed beyond shading to keep the homes comfortable when the outdoor temperatures soar.
Interview with Andy Marlow
Ben Adam-Smith has started this year with a visit to see his brother in Australia and, naturally, it was a great opportunity to record some more podcasts.
On this trip Ben has three more interviews. In this episode we meet Andy Marlow, Director at Envirotecture, who designed Sydney's first Passivhaus in Thornleigh in 2018. He has since been involved in numerous new build and EnerPHit projects, all of which require an element of cooling. In today's chat, Andy gives us an insight into Australia's current housing stock, explains why Passivhaus is a logical choice for creating healthy and comfortable homes, and he outlines the main ways to incorporate cooling into a Passivhaus build.
The ‘look' of a home tells you nothing about its quality
Andy describes the majority of Australia’s houses as “fancy looking sheds”.
With a warmer climate in many parts of the country there is a culture of opening all the doors and windows, and creating a wonderful indoor/outdoor lifestyle! In reality, temperatures are frequently unpleasant as is the humidity and, due to the poor standard of construction, there is no refuge indoors.
In fact most houses in Australia will rely on mechanical cooling via ducted air conditioning units. Because the houses are poorly insulated, the coolth generated often escapes the house, meaning that these systems operate incredibly inefficiently.
Andy also points out that Australia not only builds the largest houses in the world with the national average being 244 square metres (3x the UK average) but also the cheapest per square metre. This poses quite a challenge for the uptake of Passivhaus because it is going to be slightly more expensive than a traditional build which may in turn lead you to reduce the floor area (which many Australians may not be keen to do).
A skills shortage is impacting the quality of homes
Australia is also facing a skills shortage in the construction industry because of a nationwide shift towards higher education. Whilst this has many other benefits, the impacts on construction means it can be harder to find contractors and with less competition, they are able to charge a higher price for a lower standard of work. This is not the case for everyone or everywhere in Australia, but Andy does think this has had a significant impact on the quality of the current housing stock.
In some climates cooling will be required
Although the Passivhaus methodology is the same no matter where you are in the world, in Sydney's climate the challenge is more about cooling than heating.
Good design can reduce the risk of overheating
Andy explains that carefully placed and smaller windows can have a big impact in reducing the need for cooling. Likewise shading from an eaves overhang or external blinds will help. Natural cooling and cross ventilation by opening tilt turn windows can also work if temperatures drop overnight. However, it is not uncommon for Australia to reach 40 degrees, so there is often also a need for mechanical cooling systems.
“The biggest practical issue that we face as architects and designers in Australia is the expectation around the size of windows and doors. A lot of it comes back to that indoor/outdoor lifestyle and people's desires, expectations, and beliefs around that. Basically, you hit a point where it doesn't matter how good the glass is or how good your eaves are, you start needing to use external blinds or things that are directly adjacent to the window to keep the sun off them. You also just hit a point where regardless, there's just too much glass.”
When looking at cooling, energy efficiency is key
Because of the efficiency of Passivhaus homes, they can work very well in partnership with air conditioning systems. In much of the current housing stock, air conditioning units supply the cool air to each room of the house through a duct system. Due to the fact that these houses are poorly insulated, a large proportion of this cool air is lost though the walls, ceiling, etc. making the whole system inefficient. The high performance fabric of a Passivhaus means very little of this cool air will be lost and as a result, the cold air can be delivered in one or two areas and spread throughout the whole house naturally or through the ventilation system.
“Every one of the certified Passivhauses that we've done have mechanical cooling. It's very, very common here. 86% of new houses in Australia have mechanical cooling.”
On top of this, the MVHR removes the heat from the fresh, incoming air but retains the coolth from inside the house. This massively reduces the amount of energy needed to cool a house. With higher temperatures every year as a result of climate change, Passivhaus is an excellent option to reduce the energy demand and keep homes cool.
A Passivhaus will be comfortable in all climates
Andy explains that they always design their Passivhaus homes to stay between 20-25 degree celsius internally, but some clients may ease off on the cooling, save a bit of money and just live in a slightly warmer house. It's down to personal preference.
There is a big range of outdoor temperatures in Australia (over the course of the year) and it is common for most parts to reach 40 degrees during the day at some point, possibly reducing to 5 degrees at night during the coldest times. However, there are also areas in the mountains that can get down to -10 degrees so each project must take into account the local climate data.
Health and comfort benefits are key drivers
Most of Andy's clients have been people who have lived abroad and experienced the standard of housing in other countries. In returning to Australia, they realise how low the standard is in the current housing stock and set out on new build or retrofit projects to try and change this.
“It's the hardest part of everything we do without a shadow of a doubt, we joke that 5% of our job is design and the 95% is making stuff happen. It's mostly successfully sold when people comprehend the benefits and the benefits have nothing to do with the money. It's mostly around the health and comfort. That's partly because of the quality of everything else that exists: if I don't do this, what will I end up with? And the answer to that is normally too hot, too cold, too mouldy. If you don't want that, you end up in this long discussion, which concludes you need to build something that looks remarkably like a Passivhaus.”
Sydney's first Passivhaus: Thornleigh
Andy worked to deliver Sydney's first Passivhaus in 2018:
“It's in the middle of suburban Sydney. It's got a massive five metre wide north facing window in it. Interestingly, it's got no eaves on it, which was a deliberate choice, but it's got external blinds on it. We did it for a whole host of reasons, to get as much solar gain as we could in winter and the blinds give us real control during the summer. They come at a price obviously, but everything in building comes at a price. However, they also require the occupants to use them, so there's no point having a blind if someone doesn't press the button for it to come down. These clients are incredibly active in the management of the house, so it works like a charm.”
Renewables are common, energy efficiency is not
A large proportion of Australia’s houses are fitted with solar PVs and the majority of new builds have them as a requirement, which is economical for a country with so much sun. However, with an inefficient housing stock they are consuming a lot of energy every day. The challenge is therefore not solely focused on how energy is generated but also how much is consumed.
“A lot of big inefficient houses with big air conditioners, while they might make a lot of electricity at various points, in the middle of big electricity spikes, they're going to struggle. But also when the system crashes, then they're completely stuffed.”
There has been a recent shift towards batteries as people are deciding to prioritise personal resilience, but also because the feed-in tariffs supplied by energy companies have dropped quite significantly and it no longer feels worth it. If Passivhaus became mainstream in Australia, the combination of energy-efficient homes and personal renewable resilience would put them in an excellent position to face incoming climate challenges.
The conversation around embodied carbon
Andy highlights that in Australia, the national conversation on embodied carbon is behind the curve. There is a reliance on concrete for building foundations and the houses are often large. However, the default approach to building is with timber frame meaning they don’t face the same challenge as the UK in needing to transition away from brick and block construction.
The Australian construction industry relies on imported materials
Australia imports a lot of supplies for low energy projects and as a result 80% of a house might need to be sourced elsewhere. Materials such as glass, insulation, membranes, mechanical ventilation systems/ducting and any new technological developments are all brought into the country and are therefore expensive items. Australia does have a large timber industry so wood is more easily accessible but there is still a reliance on imports to meet demand.
Some materials that are commonly used in the UK such as I-joists are not as needed in Australia because their buildings don’t require as much insulation. Andy notes that 140mm stud walls often offer a sufficient wall thickness in order to meet Passivhaus standard. Wood fibre board would be a great material for Australian Passivhauses to eliminate thermal bridges but it is bulky and as a result expensive to import.
Design approaches: new build and retrofit
Andy explains the process he would take when beginning a Passivhaus project:
- Design brief – Setting the parameters for what we are trying to achieve. Why are you doing this? What do you want? And for retrofit, what’s wrong with the house right now?
- Work out the practical details – What is the building going to look like? How is it going to get built? Is it a professional builder or a self build project?
- Design development phase – Get as many details as possible in place as early as possible because once it has been taken to planning, it can be hard to change.
- Post planning – Focus on the detailing, construction documentation and refining interiors.
“We spend a lot of time getting our interiors to absolutely sing because that's the stuff you end up looking at every day.”
New builds go pretty smoothly. The most common time for issues to arise is during groundworks when something is uncovered that no one knew about, but most of the time the process is smooth. In the case of retrofit projects, Andy explains that he prefers to wait until the building has been stripped back to work out the specifics of the technical design as you never know what you will find hidden behind the walls. There have been many occasions where this stage has uncovered issues that show their original plan wouldn’t work and a different approach was needed. Andy recommends creating an overarching design which includes the materials you plan to use before you begin to dismantle the existing structure so you have an idea, but to avoid trying to plan out specific construction methods or details before this step, as you will likely end up having to repeat the process.
Envirotecture currently have 2 EnerPHit projects certified and many more in the works.
Recommendation is still the best way to find good builders
Envirotecture has developed relationships with a number of builders over the years and so that will tend to be the first avenue they explore. However if you are going into a new area, Andy follows these three steps:
- Seek recommendations from people you know and trust.
- Use the list of certified tradespeople on the Australian Passivhaus Association database.
- If the other two steps have been fruitless, ring people in the area and ask a “dumb question” that will highlight how much they really know about Passivhaus – this will help you find the people who buy into the approach and commit to the attention to detail necessary.
The team you assemble doesn't necessarily need Passivhaus experience, but they do need to be enthusiastic and have an interest in learning.
Knowledge is key
Andy offered some overarching advice to anyone who might want to take on a Passivhaus project:
“Knowing as much as you can before you start is the key. Ask lots of questions of people who should know decent answers and if you don't understand the answer, ask the same person again. If it still doesn't make sense, ask someone else. The more competent professionals you surround yourself with, the easier that's going to be. It is significantly cheaper, and easier and less stressful to learn from other people's mistakes, I would recommend leveraging them as much as possible. You will make some of your own, everyone does, realise them as quickly as you can, learn, move on, try not to do it twice!”
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