How Do You Retrofit a Melbourne Home to Be Genuinely Energy Efficient?
Bolting solar panels onto a leaky old house and calling it energy efficient is like strapping a turbo onto a car with four flat tyres. Most Melbourne renovations chase the shiny stuff, the panels, the new split system, the smart thermostat, and completely ignore the shell. The shell is the only thing that actually decides whether the house is warm or a money pit.
You retrofit a Melbourne home for energy efficiency by fixing the shell first. Airtightness, insulation, better windows and thermal bridges come before solar or a new heater. Seal it, insulate it, then add heat recovery ventilation so it breathes. Done right and tested, a retrofit transforms how the house performs.
Carland Proof Point: Our Retrofit Rifle EnerPHit in Williamstown, a thirty year old home, tested at 0.43 ACH50, more than forty times tighter than the average Melbourne house.
What does energy efficient actually mean in a retrofit?
It means measured performance, not a feeling. A genuinely energy efficient retrofit has numbers behind it. How much air leaks out of the house, measured in air changes per hour. How much energy it needs to stay warm, measured in kWh per square metre per year. If your renovation can't be described in numbers like those, it isn't energy efficient, it's just newer.
This is where a certified retrofit separates itself from a cosmetic one. We model every retrofit in PHPP, the Passive House Planning Package, which is the energy software the whole certified world runs on. It takes the real geometry of the house, Melbourne's actual climate data, the measured airtightness result, and the thermal performance of every wall, roof and window, and tells you exactly how the home will perform before you spend a dollar on site. Our Retrofit Rifle EnerPHit modelled a heating demand of 31.5 kWh per square metre per year. That is a hard, certified figure, not a sales pitch.
A star rating on a standard renovation tells you what the drawings hoped for. A blower door test and a PHPP model tell you what the house actually does. Which one would you rather bet your energy bills on?
Why does the building shell matter more than solar panels?
Because a solar panel on a leaky house is a bandaid on a broken leg. It generates energy while the house throws heat out through every gap and cold wall it has. Fix the shell first and the house needs so little energy that the solar has a fighting chance of actually covering it.
Get the order right. Airtightness, insulation, windows and thermal bridges come first, because they cut how much energy the house needs in the first place. Only then do you size the heating and add the solar. Do it the other way around and you are paying to heat air that is escaping through the walls, which is the single most expensive way to run a home.
The average Melbourne home leaks at around 19 ACH50 (CSIRO and Australian Building Codes Board, 2016 airtightness study). Our Retrofit Rifle EnerPHit came in at 0.43. Same job, thirty year old bones, but the leakage cut by more than forty times before a single panel went on the roof. That is what fixing the shell does.
If your builder wants to talk solar before he's talked airtightness, what problem is he actually solving?
How airtight can you actually make an old house?
Tighter than most people believe, and it's the cheapest big win in the whole retrofit. Air leakage is what makes an old house feel cold and drafty no matter how hard the heater works. Seal it properly and the difference is immediate.
The certified retrofit standard, EnerPHit, allows airtightness up to 1.0 ACH50, which is deliberately more forgiving than the 0.6 limit for a new Passive House, because you are working with a building that already exists and has thirty years of quirks baked in. Our Retrofit Rifle EnerPHit didn't just scrape in at 1.0. It hit 0.43, less than half the limit, tested on an independent blower door machine after the work was done.
How? A continuous airtight layer, taped and sealed at every junction, using Proclima membranes and tapes. It is fiddly, unglamorous work, the stuff behind the walls that no one ever sees, and it is exactly the work that decides whether the house performs. You cannot photograph it for the socials, but you can measure it.
If nobody ever puts a blower door in your finished retrofit, how will you know the sealing was done properly, or done at all?
What about insulation and thermal bridging in an old home?
This is where honesty separates a real retrofit from a spray-foam-and-hope job. You can insulate an old house beautifully in the places you can reach, and there are places you simply cannot. A good retrofit builder tells you which is which instead of pretending the whole thing came out perfect.
On our Retrofit Rifle EnerPHit we rebuilt the walls to a U-value of 0.273 W/(m²K) and the roof to 0.247 W/(m²K), both a world away from the bare brick and thin batts they started as. A lower U-value means less heat escaping, so those numbers matter. But the existing concrete slab stayed at 1.045 W/(m²K), because you cannot rip out and re-pour a thirty year old slab without demolishing the house. We insulated the edges and detailed around it, but we didn't pretend it disappeared. That is a thermal bridge, a weak spot where heat sneaks out, and managing it honestly is part of the job.
The trap in old-home retrofits is thermal bridging, all those junctions where the insulation has to stop and start around existing structure. Get them wrong and you don't just lose heat, you invite condensation and mould into the wall. Getting them right is most of the skill.
If your retrofit quote promises a perfect result on a hundred-year-old house with no compromises, what is it not telling you?
Do you still need good windows and mechanical ventilation?
Yes to both, and the ventilation is not optional once you seal a house up. Old timber windows are usually the biggest hole in the shell after air leakage, and a sealed house with no fresh air supply is a house with a moisture problem waiting to happen.
On the Retrofit Rifle EnerPHit the windows went in at an installed U-value of around 1.25 W/(m²K), meeting the EnerPHit window target, which for a retrofit is a serious jump in comfort and a stop to the condensation that pools on old single glazing. Then the ventilation. Once a house is genuinely airtight it needs a mechanical lung, so we fitted a Zehnder heat recovery unit running at an effective 87% heat recovery. That means it pulls 87% of the warmth out of the stale air being pushed outside and puts it into the fresh, filtered air coming in. You get constant fresh air without opening a window and without throwing your heating out with it.
Seal a house tight and skip the ventilation and you haven't built an energy efficient home, you've built a very well sealed mould box. Does your retrofit plan actually include a way for the house to breathe?
What kind of results can a proper retrofit actually deliver?
A house that performs closer to a new certified build than to the tired old home it started as. That is the whole point of doing it properly, and it is measurable, not a promise.
Here is what our Retrofit Rifle EnerPHit in Williamstown, a thirty year old home, actually achieved, every figure from the certified PHPP file. Airtightness of 0.43 ACH50 against a 1.0 limit. A modelled heating demand of 31.5 kWh per square metre per year. Heat recovery ventilation running at 87%. And with rooftop solar, the home now generates more renewable energy across the year than it uses, which earns it EnerPHit Plus classification.
For comparison, a brand new Certified Passive House like our Pigeon Passive House in Yarraville models a heating demand of 9.0 kWh per square metre per year. So a retrofit lands higher than a new build, and it should, because you cannot rotate an existing house to face north or start its slab from scratch. But 31.5 against a standard old Melbourne home that was never tested, never modelled and leaked like a tent is a different universe of comfort and running cost.
If someone could take your draughty old house and make it perform like that, why would you settle for a paint job and a new kitchen?
What are the common mistakes people make retrofitting for energy efficiency?
Most of them come from doing the fun bits before the important bits. The ones that catch people out:
Putting solar on the roof before sealing and insulating the shell underneath it.
Skipping the blower door test, so nobody ever knows if the airtightness work was actually done.
Sealing the house tight without adding proper ventilation, which turns a warm home into a mould problem.
Buying cheap windows to save money, then living with the condensation and heat loss for the next twenty years.
Believing a builder who promises a flawless result on an old house and won't talk honestly about the slab, the thermal bridges, or what can't be fixed.
Which of those is hiding in the retrofit quote sitting on your kitchen bench right now?
So what should you actually demand from an energy efficient retrofit?
If your retrofit can't be described in a blower door result and a heating demand figure, it isn't energy efficient, it's just redecorated. So what number did your builder promise you, and who's going to test whether he hit it?
By Matthew Carland, certified Passive House builder and director of Carland Constructions. Five certified Passive House and EnerPHit projects in Melbourne, including a thirty year old home taken to certified retrofit standard.