Forrest Passive House: our first certified Passive House, and everything it taught us
One morning over Christmas 2019, during the Black Summer bushfires, smoke rolled into Melbourne. In a house in Spotswood, the air quality monitors that had been set up to understand how the home was performing spiked straight off the charts, and that reading changed the whole project.
The job had started as a $550,000 alterations and additions project, designed by Altereco Design. One of the owners has a respiratory sensitivity, and that smoky morning made it clear that a better insulated version of the same old house was never going to give them the clean air they needed. Once we had priced and modelled that plan, we had an honest conversation with them: it would cost a lot of money for not much more comfort. So the question became, what would a new build look like?
A day later they said yes to knocking it down and building a certified Passive House. It was a first for them, and a first for us too.
Moving a house instead of bulldozing it
Knocking a house down usually means paying someone to smash it up and send it to landfill. These owners did something smarter. The old house was cut into three sections, loaded onto trucks and taken out to a new life in regional Victoria. Instead of paying for demolition, a house relocation can actually pay you.
I'll be honest, I didn't think it would work. The street is tight, and pulling a house out of it seemed a bit crazy. It was stressful for the blokes driving the trucks, but out it came, and we had a clean site to start on.
A floor that sits on removable steel feet
Instead of concrete stumps set in mass concrete, the house sits on a steel footing system that goes in without digging and pouring concrete. It went in quicker, made far less mud and mess, and it can be pulled out and recycled one day, leaving the site almost as if nothing was ever there.
On top of that we built our first ever Passive House subfloor. We wrapped the whole floor in a Pro Clima membrane, treating it like a wall that needs protecting from the weather, then packed in two overlapping layers of R2.5 batts between the joists for R5 all up. With thunderstorms on the radar, the team had the whole floor insulated, sheeted and protected in two days.
Learning every detail as we went
This was our first certified Passive House, and we had to learn a lot of it on the run. We underestimated the labour in our costing, and the detailing took longer than we planned. But every hour we spent here has paid us back on every job since.
The walls are 140 mm studs at 600 mm centres instead of the usual 450, so there is less timber and more insulation, with the noggins turned on their edge so the insulation runs continuously. A 45 mm service cavity on the inside keeps electricians and plumbers from cutting holes in the airtight layer. The windows are triple glazed, set back within the insulated part of the wall, sitting up on packers above a back dam so any water drains out and away. Even the little clips that hold the windows in were cut down and crimped so they wouldn't pierce our tape.
Our trades had to change habits too, like drilling five small holes for five cables instead of one big one so each could be sealed. They didn't complain. They wanted to learn, and they've been doing it that way ever since.
120 people and a live blower door test
In July 2022, halfway through the build, we opened the house up for Open House Melbourne and over 120 people came through across two sessions. Drew from Passive Tech ran a blower door test live in front of everyone, which is a bit like sitting an exam with your family watching. Our first test mid build came in at 0.34 air changes an hour.
The final test was in February 2023, with the house finished. It came in at 0.42 under depressurisation and 0.41 under pressurisation, an average of 0.41, well under the Passive House limit of 0.6 and around 46 times tighter than the average Melbourne home. I was off getting married during those last few weeks, and the team finished the job without me, which tells you everything about the crew I've got.
What it's like living in it
A couple of months after they moved in, on a cold Melbourne morning, I messaged the owners to ask how they were finding it. The reply was that they were both in short sleeves, enough said, and they still hadn't turned the heater on.
They told us the house feels peaceful, the triple glazing blocks out the noise from outside, and they are sleeping better with fresh filtered air coming in all day and night. That matters in Spotswood, which sits next to some of the most polluted air in Melbourne from traffic, industry and the port. After spending a few weeks overseas in winter, they came home to find the inside temperature hadn't really moved.
What we changed after Forrest
Forrest became the blueprint. On Champion Passive House, the very next subfloor, we swapped the noggins around the perimeter for one continuous beam the joists slip into, which also made setting out much easier, and we moved to a narrower 1.5 metre roll of membrane because the 3 metre roll was a nightmare in the wind. Small changes like that only come from doing it once properly and paying attention.
The certified numbers
Every figure below comes from the certified PHPP (the Passive House Institute's energy modelling tool), checked by an independent certifier, with airtightness taken from the on site blower door test.
| Measure | Forrest Passive House | Passive House Classic requirement |
|---|---|---|
| Airtightness (ACH50) | 0.41 | 0.6 or less |
| Heating demand (kWh/m² per year) | 13.1 | 15 or less |
| Cooling demand (kWh/m² per year) | 3.3 | 15 or less |
| Renewable primary energy (kWh/m² per year) | 37.4 | 60 or less |
| Solar generation (kWh per m² of footprint per year) | 56 | No requirement for Classic |
| Hours above 25°C | 5.7% | 10% or less |
| Treated floor area | 149.3 m² |
What's in the walls, roof and floor
- Walls: 140 mm timber studs at 600 mm centres with R4.0 batts, a 45 mm service cavity with R1.0 batts, Pro Clima membranes and plasterboard, U value 0.258 W/m²K
- Roof: deep R7 batts in the trusses plus more in the ceiling, U values from 0.105 to 0.157 W/m²K
- Floor: timber subfloor on removable steel footings, wrapped in a Pro Clima membrane with two layers of R2.5 batts, U value 0.259 W/m²K
- Windows: Kömmerling C70 frames with Viridian Lightbridge triple glazing, average installed Uw 1.275
- Ventilation: Zehnder ComfoAir Q350 heat recovery ventilation, 80% effective heat recovery
- Energy: all electric with an 18 panel, 6.66 kW solar system expected to generate 9,378 kWh a year
How it stacks up against our other certified homes
| Project | Airtightness (ACH50) | Heating demand (kWh/m² per year) |
|---|---|---|
| Pigeon Passive House, Yarraville | 0.26 | 9.0 |
| Champion Passive House, Williamstown | 0.39 | 13.8 |
| Forrest Passive House, Spotswood | 0.41 | 13.1 |
| Wellington Passive House, Flemington | 0.47 | 13.4 |
| Parade Passive House, Ascot Vale | 0.49 | 14.8 |
Our Retrofit Rifle EnerPHit in Williamstown is left out of the table because it is certified to the separate retrofit standard.
The team behind it
Design and Passive House modelling by Altereco Design, certification by Emilia Iacovino of Detail Green, airtightness testing by Drew Kroker of Passive Tech, and a long list of trades who were willing to learn a new way of building, with Carland Constructions as the builder. The house has since been on the front cover of Sanctuary magazine and featured in Passive House Plus, the international Passive House magazine.
If you are weighing up an extension against a new build in Melbourne, book a call and we will give you the same honest answer we gave these owners.
Frequently asked questions
What is Forrest Passive House?
Forrest Passive House is a 149.3 m² home in Spotswood, Melbourne, and the first certified Passive House built by Carland Constructions. It was designed by Altereco Design and certified Passive House Classic by Detail Green in March 2024, with an airtightness result of 0.41 ACH50 and a heating demand of 13.1 kWh/m² a year.
What is it like building a Passive House for the first time?
It takes more planning and more labour than you expect. On Forrest Passive House, Carland Constructions underestimated the labour, learned many details on the run and retrained trades in small habits like sealing every penetration, but still hit 0.41 ACH50 and used every lesson to improve the next build.
How long does it take to build a Passive House in Melbourne?
Forrest Passive House took about a year on site, from the old house being relocated in March 2022 to handover in March 2023. Certification followed in March 2024 once the final paperwork and test results had been reviewed.
Can you relocate an old house instead of demolishing it?
Often, yes. At Forrest Passive House the original home was cut into three sections and trucked to a new site in regional Victoria instead of going to landfill. Houses on stumps, with lightweight cladding and good site access, are usually the easiest to relocate, and the owner can be paid for the house rather than paying for demolition.
Can a smaller home be a certified Passive House?
Yes. Forrest Passive House has a treated floor area of 149.3 m² and met the Passive House Classic standard with a heating demand of 13.1 kWh/m² a year. Smaller homes have more outside surface for their size, so the detailing has to be just as careful.