What Is Passive House? A Melbourne Architect Explains How It Works

Passive House is one of the world's most rigorous and well-established building-performance standards.

It starts with a relatively simple idea: make the building itself exceptionally good at maintaining comfortable, healthy indoor conditions, and the heating and cooling systems have far less work to do.

For a family living in one, the result should feel much simpler than the technical process behind it.

The bedroom does not become cold overnight in winter. You can sit beside a large window without feeling chilled by the glass. The windows and bedroom door can remain closed while fresh filtered air continues to enter the room. When Melbourne reaches 38 degrees outside, the house gains heat much more slowly and the cooling system has a far easier job.

That experience is what interests me most about Passive House.

Its exceptionally low energy demand is important, but I regard that as one of the consequences of creating the indoor environment properly. If a home needs far less energy for heating and cooling, supplying more of its total energy from rooftop solar and batteries also becomes considerably easier.

What does living in a Passive House actually feel like?

Imagine a normal winter morning in Melbourne.

You get out of bed and the room has not dropped dramatically in temperature overnight. Walking past the bedroom window does not create the familiar sensation of cold radiating from the glass.

The window and door may have been closed all night, yet filtered outside air has continued to enter through the ventilation system.

Later in the year, on a beautiful spring afternoon, you open the doors and windows because you want the breeze and connection with the garden. Passive House does not stop you doing that.

Then consider the same house during a run of very hot summer days. External shading keeps direct sun away from vulnerable glazing. Good insulation slows heat entering through the building. The house is carefully sealed against uncontrolled hot air leaking inside.

Cooling may still be used, particularly in Melbourne's increasingly hot summers, but the building itself has already done much of the work.

I have spoken to Passive House owners about what this feels like after they have lived with it for some time, and their answers are often more revealing than the technical descriptions.

I have heard owners say they spend Melbourne winters at home in shorts and T-shirts. The internal conditions become so consistent that they sometimes open the front door to go outside and realise they have completely misjudged what they need to wear.

One owner told me the temperature feels essentially the same everywhere in the home, all the time. Another told me that after three years of living in their Passive House they had never turned the heater on.

That is an individual owner's experience rather than something every Passive House can promise, but it gives you some idea of how different the relationship between the house and the weather can become.

The quietness also catches people by surprise.

I have heard an owner talk about almost forgetting that a neighbour who used to keep them awake at night was still there. Others comment on how little traffic and external noise they hear once they are inside.

And there is one characteristic I have noticed repeatedly.

Passive House owners tend to be incredibly proud of their homes.

Sometimes slightly evangelical.

If you meet somebody who owns one, there is a fair chance you will hear about it whether you asked or not.

I actually think that tells us something important. People rarely become passionate advocates for insulation or window specifications. They become advocates for how the finished home feels to live in.

Where did Passive House come from?

The original German name is Passivhaus.

The world's first Passive House project was built in Darmstadt-Kranichstein, Germany, in 1990–91, and the homes have been occupied since 1991. The Passive House Institute was founded by physicist Professor Wolfgang Feist in 1996.

Although its origins are European, Passive House is not a European style of architecture.

It is a performance standard.

A Passive House can be contemporary or traditional, large or small, masonry or timber. Solar panels do not make something a Passive House, and it is different from what Australians generally mean by passive solar design.

The standard sets measurable requirements for how the building performs and leaves the architect and project team to determine how those requirements are achieved.

Think of the house as a very good coat

The simplest mental model I know is a good winter coat.

Your body is already producing heat. A good coat does not create that heat. It makes it much harder for the heat to escape.

Buildings are similar.

A conventional house can lose heat through the roof, walls, floor, windows and uncontrolled gaps. We then keep replacing that lost heat with a larger heating system.

Passive House works on the building first.

Insulation slows heat moving through the walls, roof and floor. Airtight construction stops outdoor air moving through random gaps. High-performance windows improve one of the traditionally weakest parts of the building envelope. Careful detailing deals with places where heat might otherwise find an easy route through the construction.

Once the building becomes extremely good at holding the conditions we want, heating and cooling become much smaller tasks.

There is also a long-term benefit to putting that quality into the building itself.

Heating and cooling equipment will eventually be replaced. Solar and battery technology will change dramatically over the life of a home.

A well-designed wall, roof and window installation can continue doing its job for decades.

Good insulation does not need someone to remember to turn it on.

Why is it called Passive House?

The word passive can be slightly misleading.

It does not mean the house has no technology, no heating or no mechanical systems.

The idea is that the building itself does much more of the work passively.

Its insulation, orientation, windows, airtightness and shading help maintain the indoor environment before an active heating or cooling system has to intervene.

A conventional house may use a powerful mechanical system to compensate for a building that gains and loses heat quickly.

Passive House reduces the problem first.

The remaining heating and cooling requirement can then be surprisingly small.

Airtightness does not mean living in a sealed box

Passive Houses are extremely airtight.

You can still open the windows whenever you want.

On a beautiful spring morning in Melbourne, I would expect you to.

Airtightness means that when you close the windows and doors, the building is actually closed.

Many conventional homes contain thousands of small gaps around windows, services, roof spaces and construction junctions. Air moves through them whether the occupants want it to or not.

Sometimes you experience that directly as a draught.

Passive House removes as much of that uncontrolled leakage as possible.

For certification, the completed building must achieve no more than 0.6 air changes per hour when pressure tested at 50 Pascals. That is dramatically tighter than a typical Australian home.

You do not need to understand the mathematics to understand why I value this.

The important part is that there is a number.

We test it.

A large calibrated fan, called a blower door, is temporarily fitted into an external doorway. It pressurises and depressurises the house so that we can measure how much air is leaking through the building.

If it leaks too much, we find out where.

I like that accountability.

If the house is airtight, how do you get fresh air?

Deliberately.

A Passive House normally uses mechanical ventilation with heat recovery.

Fresh outside air is filtered and continuously supplied to bedrooms and living areas. Used air is extracted from bathrooms, laundries and other places where moisture and smells are produced.

As the outgoing air leaves, a heat exchanger transfers much of its useful heat to the incoming fresh air. The two air streams remain separate.

For a family, the building science is less interesting than the result.

A child's bedroom can remain closed overnight and still receive fresh filtered air.

You are not relying on a cold open window in July or accidental leaks around the window frame to ventilate the room.

Airtightness and ventilation have to work together. Australian Government guidance similarly distinguishes intentional ventilation from uncontrolled air leakage and notes that increasingly airtight homes need reliable ventilation to maintain indoor air quality.

Why do Passive Houses use better windows?

Think about sitting beside a large window on a cold Melbourne evening.

The thermostat might say 21 degrees, yet you still feel uncomfortable beside the glass.

Comfort is influenced by the temperature of the surfaces around us as well as the temperature of the air.

Cold glass can make your body feel as though it is losing heat towards it.

Passive House uses very high-performance windows with appropriate glazing, insulated frames, excellent seals and careful installation.

The inside surface of the glass stays much warmer in winter.

That affects how the architecture can actually be used.

A beautiful window seat is far more useful if nobody avoids sitting there for three months of the year.

What is a thermal bridge?

You will encounter this term frequently when reading about Passive House.

A thermal bridge is simply a place where heat has found an easier path through the building.

It might occur where an uninsulated concrete slab extends from inside to outside, where steel passes through the insulated wall or around a poorly resolved window installation.

Imagine a well-insulated wall with one small area that becomes significantly colder than everything around it.

Apart from losing heat, that colder internal surface can matter because warm indoor air contains moisture. If that moisture repeatedly encounters a sufficiently cold surface, condensation can occur, and persistent moisture can create conditions in which mould grows.

Passive House makes us resolve those junctions before they disappear inside the finished building.

The large uninterrupted part of a wall is usually quite straightforward. The difficult work is where one building element meets another.

We effectively build the house mathematically before we build it physically

This is one of the aspects of Passive House I value most as an architect.

We model the home in considerable detail before construction.

The principal design tool is the Passive House Planning Package, usually called PHPP.

It includes the local climate, building form, orientation, windows, shading, insulation, ventilation and many other characteristics of the proposed home.

That gives us a way to investigate architectural decisions rather than relying solely on intuition.

Imagine a site with an exceptional view towards the west.

Architecturally, a large window may be exactly what the house wants.

Passive House does not prohibit that window. It makes us quantify what the window does.

We can investigate how much unwanted summer heat it introduces, whether external shading materially improves the result and what happens when we change the glazing or the size of the opening.

We may decide that the large window is worth having.

The building physics stops us making that decision blindly.

What does this look like on a real family home?

At Estuary House in Mt Martha, Passive House performance is being pursued within a substantial 392-square-metre family home rather than a small experimental building.

The brief still had to resolve accessibility, family gatherings, the relationship with the landscape and the quality of the individual rooms.

Those architectural ambitions did not disappear because we were designing for high performance.

Passive House gave us another layer of information against which those decisions could be tested.

I do not want to design a technical object and ask the family to adapt their lives around it.

I want to design an excellent family home and understand, in considerable detail, how that home is likely to perform.

How do we know the finished house actually works?

Modelling predicts what should happen.

Certification and testing help determine whether what was actually built matches those intentions.

A house cannot become a Certified Passive House simply because its architect or builder describes it that way.

The Passive House Institute establishes the certification criteria and accredits building certifiers around the world. Those certifiers can certify buildings on behalf of the Passive House Institute and in accordance with its criteria, while remaining independent from the designer of the particular project they certify.

The design and PHPP model are reviewed. Construction evidence is assessed. The completed building has to pass its airtightness test and provide the evidence required by the certification process.

Certification therefore means something quite specific.

An independent party has checked the evidence against a defined standard.

That is different from phrases such as “Passive House inspired”, “designed using Passive House principles” or simply “high performance”.

Those descriptions may still refer to very good buildings. Borland Architecture also applies high-performance principles on projects where formal certification may not be pursued.

They are simply different claims.

Does Passive House make the design process very complicated?

There is considerable technical work behind it.

The homeowner should not need to manage that complexity.

When an architect and construction team understand Passive House, those considerations become part of the design process from the beginning.

Even something apparently simple, such as moving a window, can affect solar gain, shading, the way the opening is detailed and the energy model.

That is much easier to resolve while the architecture is developing than after the design has already been completed.

If Passive House is an ambition for a project, I would prefer to know that at the beginning.

The experience of the project team matters because much of the apparent complexity becomes a normal part of making design decisions once the process is understood.

Does Passive House dictate what the architecture looks like?

No.

The performance standard does not prescribe an architectural style.

We can still design generous rooms, large areas of glazing, strong connections with landscape and architecture that responds specifically to the family and site.

What changes is the amount of information available when we make those decisions.

A dramatic view may justify a difficult window orientation. An unusual building form may be worth the additional effort required to make it perform.

Passive House allows those consequences to be understood rather than hidden.

Is Passive House mainly about reducing energy bills?

I would start with comfort and health.

Very low energy demand then follows from creating a building that is exceptionally good at maintaining those conditions.

Solar panels increase the amount of energy we can produce at home.

Passive House reduces how much energy the building needs in the first place.

That combination can make a much higher level of energy self-sufficiency achievable.

It does not guarantee it. Hot water, appliances, pools, electric vehicles and the way a family lives all consume energy as well.

But heating and cooling no longer need to compensate continually for a building that is losing the conditions we are trying to create.

Does Passive House cost more?

Generally, yes, compared with an otherwise similar conventional home.

Passive House requires a very high standard of building quality.

High-performance windows, better insulation, airtight construction, mechanical ventilation, modelling, careful detailing, testing and independent certification all carry a cost. The people constructing the home also need to work with greater care.

I would not expect one of the world's most demanding building-performance standards to cost the same as a conventional volume-built home primarily designed around minimum regulatory requirements and a highly competitive construction price.

Cost is still heavily influenced by the architecture.

A compact, thoughtfully designed Passive House can be more economical than an extremely complex conventional architect-designed home.

This deserves its own detailed article because the useful question is not simply whether Passive House costs more. It is how much more, where that money goes and what value the family receives in return.

We have also been working on this challenge through Stllhaus, where repeating a carefully resolved high-performance building system allows much of that design and detailing effort to be spread across multiple homes rather than reinvented for every project.

That is a different conversation, but an important one if high-performance housing is going to become accessible to more families.

What should living in one ultimately feel like?

Once the family moves in, most of the modelling, construction detailing, certification and testing should disappear into the background.

The bedroom can remain closed overnight and still feel fresh in the morning. Sitting beside the glass in July no longer has to mean feeling cold. The temperature throughout the house can become remarkably consistent, and Melbourne's weather outside has much less influence on what is happening inside.

You may even have to remind yourself to put on a jumper before walking out the front door.

And based on the owners I have spoken to, there is one other possibility worth mentioning.

You may find yourself becoming the person at dinner parties who explains Passive House to people who never actually asked.

That experience is why Passive House interests me.