How a Passive House is built to the standard in Adelaide

A Passive House is not built and then tested. It is calculated, then built to match the calculation.

That is the single idea most people miss. A conventional home is drawn, costed and built, and its energy performance is whatever it turns out to be. A Passive House inverts the order: the performance is modelled first, in detail, and the build is the act of making the model true. The number comes before the wall.

This is the how-it-is-built companion to our Passive House approach — the pillar that explains what the standard is and why we build to it. Here we walk through the sequence itself, from the spreadsheet to the blower door, the way it actually runs on an Adelaide site.

A note on language first. We build to the Passive House standard and its principles, and we hold Certified Passive House Tradesperson accreditation from the Passive House Institute. That is a deliberate distinction: the standard is the target we design and detail to, and certification is a separate, independent process. The two are not the same thing, and we are careful not to blur them.

How is a Passive House built, step by step?

It is modelled, then built to the model, then verified — in that order.

The sequence is always the same, whatever the site: model the design in PHPP, build a continuous airtight layer, wrap the home in continuous insulation, design out the thermal bridges, fit glazing matched to the orientation, install mechanical ventilation with heat recovery, and prove the envelope with a blower-door test. Each step depends on the one before it. Skip or rush any of them and the rest underperform — which is most of why a rated home so often misses its number.

The rest of this piece takes them one at a time.

It starts in PHPP, not on site

Every Passive House begins as an energy model, before anything is built.

PHPP — the Passive House Planning Package — is the Excel-based energy-balance tool the Passive House Institute authors and updates. According to the Australian Passivhaus Association, it is the key design tool used in planning a Passive House and the basis of verification for the standard. Every Passive House is modelled in it.

The model takes the real building — its orientation, its glazing, its insulation, its shading, the Adelaide climate file — and calculates the annual heating demand and peak heating load before a footing is poured. The targets are specific: the Passive House Institute sets a heating demand of no more than 15 kWh per square metre per year, against roughly 120 for a typical build. If the model misses, you change the design, not the paperwork — more insulation here, a smaller window there, better glass on the west.

That is what makes PHPP different from a star rating. A NatHERS rating is a prediction made once and rarely checked against the finished house. PHPP is a working tool the whole build is held against, and it is precise enough — the association puts it at plus or minus half a kilowatt-hour — to drive real decisions rather than just produce a certificate.

The airtight layer: one continuous line, taped and sealed

A Passive House has one unbroken airtight layer wrapping the whole heated space — and finding it on the drawing is the first real test of the design.

The rule of thumb is the “pencil test”: you should be able to trace the airtight line around a section of the house without lifting the pencil — through the floor, up the walls, across the ceiling, around every window and door. Where that line is broken is where air, and the moisture it carries, leaks through.

On site that line is real material. On the warm inside face of a timber-framed wall it is usually an intelligent vapour control membrane such as Pro Clima’s INTELLO, lapped and taped at every join, sealed to the slab, and dressed around every penetration — every pipe, cable, downlight and duct. The tapes and sealants are a small material cost. What they really demand is sequence and supervision: the plumber who cuts through the membrane, the electrician who runs a cable through an unsealed grommet, the plasterer who covers a join before it is taped — any one of them can undo the layer. That is the real cost of airtightness, and it is a discipline far more than a product.

Airtight is not the same as sealed shut. An airtight home still breathes — on purpose, through the ventilation system — rather than by accident through gaps. Holding that distinction is the whole game.

Continuous insulation, with no gaps to bridge

A Passive House is wrapped in continuous insulation — the operative word being continuous.

Most homes are insulated between the studs, which leaves the timber itself as a cold path through the wall and the batts compressed, cut short around services, or left voided behind a downlight. A Passive House envelope adds insulation across the structure, not just between it, so the whole heated box sits inside one thermal blanket — under the slab, in the walls, over the ceiling, with no thin spots.

The point is not a single headline R-value; it is the absence of gaps. Insulation that is generous on paper but interrupted on site performs like the weakest part of it. In our climate that wrap works in both directions: it keeps the summer heat out as much as it keeps the winter warmth in, which is exactly what a zone 5 home needs.

Thermal-bridge-free detailing: the junctions decide it

A thermal bridge is a shortcut through the insulation, and a Passive House is detailed to close them off.

A thermal bridge is any path where heat bypasses the insulation through a more conductive element — a steel lintel, a concrete slab edge, a balcony that runs straight through the wall, a junction where two planes meet and the insulation pinches. Each one leaks heat and, worse, creates a cold internal surface where moisture can condense.

The Passive House Institute treats a junction as effectively thermal-bridge-free when its linear loss coefficient — the Ψ-value — is at or below 0.01 W/mK. That is a demanding number, and it is met by detailing rather than product: lifting the slab edge onto insulation, breaking the path through a lintel, carrying the insulation line unbroken across every corner and junction. It is drawn at design stage and checked on site, because a thermal bridge designed out on paper and then bridged by a stray fixing is no longer designed out. The durability payoff matters as much as the energy one — no cold surface inside the fabric means no quiet condensation feeding mould and rot.

High-performance glazing, sized to the orientation

Windows are the weakest part of any wall, so a Passive House specifies them deliberately and places them on purpose.

Even a good window insulates far worse than the wall around it, so glazing is where a lot of the heating and cooling demand is won or lost. A Passive House uses high-performance glazing — double or triple glazed depending on the climate and the PHPP model, in insulated, thermally broken frames — installed into the airtight and insulation lines rather than slapped into a rough opening.

Orientation does as much work as the glass. In Adelaide that means generous, well-shaded north glazing to catch the low winter sun, restrained west glazing to keep the late summer heat out, and eaves and shading sized in the model rather than guessed. Get the glass and its placement right and the home stays comfortable on its own for most of the year; get it wrong and no amount of insulation elsewhere fully recovers it.

Mechanical ventilation with heat recovery

Once a home is this airtight, ventilation stops being an accident and becomes a designed system.

A Passive House supplies continuous fresh, filtered air through mechanical ventilation with heat recovery — an MVHR unit. It draws stale, moist air out of the kitchen, bathrooms and laundry, brings fresh air into the living spaces and bedrooms, and passes the two streams through a heat exchanger so the outgoing air pre-warms or pre-cools the incoming air without the two ever mixing.

The Passive House Institute requires at least 75% heat recovery for a unit to be certified as a Passive House component; the units we specify reach around 90%. That is most of the warmth, or coolth, kept rather than thrown away. The filtration matters as much here as the heat: in a climate with bushfire smoke and high pollen, the home draws its air through a filter rather than through open windows. You can still open a window whenever you like — the point of the system is that you never have to.

The blower-door test: where the standard is proven

The final step turns airtightness from an intention into a measured number.

A blower-door test seals a calibrated fan into an external doorway, pressurises and depressurises the house, and measures how much air leaks through the envelope. The Passive House Institute’s limit is no more than 0.6 air changes an hour at 50 pascals — written ≤0.6 ACH50 — and in Australia the test is run under AS/NZS ISO 9972. The number is measured on the actual building, not modelled.

We run it twice. The first test is at shell completion, while the structure is still open and a leak can be found and fixed — there is no point discovering a problem once it is buried behind plasterboard. The second is before handover, as proof. That ≤0.6 result is the line between a home built to the standard and a home that merely resembles one; it is the moment the model is shown to be true. It is the same argument we make about closing the performance gap: a high-performance home is a measured result, not a drawn intention.

What building to the standard actually involves

Stripped to its parts, building to the Passive House standard on an Adelaide site means:

• Modelling first. The design is calculated in PHPP and built to match it, not the other way around.
• One continuous airtight layer. Taped, sealed and dressed around every penetration — held together across every trade.
• Continuous insulation. Across the structure, not just between it, with no gaps or cold paths.
• Thermal bridges designed out. Junctions detailed to a Ψ-value at or below 0.01 W/mK and checked on site.
• Glazing sized to orientation. High-performance, thermally broken, with north glazing shaded and west glazing restrained for zone 5.
• Mechanical ventilation with heat recovery. Continuous filtered fresh air, with the heat exchanger keeping most of the energy.
• A verified blower-door result. ≤0.6 ACH50 under AS/NZS ISO 9972, tested at shell and again before handover.

Around all of that sits the rest of a durable wall — a ventilated cavity behind the cladding and a vapour-open weather-resistant barrier on the cold outside face — so the envelope that holds the heat also stays dry. The energy story and the durability story are built by the same details.

The order is the point

Building to the Passive House standard is not a list of upgrades bolted onto a normal house. It is a different order of operations: model the performance, then build the envelope that delivers it, then measure to prove it did.

It is also how we already prefer to build. Many of these principles — the tested envelope, the continuous insulation, the moisture detailing — are part of our baseline on the custom homes we build across Adelaide, in Henley Beach, West Lakes, Grange and Lockleys. Building fully to the standard typically adds around 10–20% over a code-minimum build, toward the lower end against the way we already work, and most of it returns over the life of the home.

The Code is a floor, and on energy it is a low one. A home is a fifty-year-plus proposition. We would rather model it, build it and measure it once, properly, than hope a drawing comes true on its own.