Where the heat actually leaves your house
Heating a house that leaks is like filling a bath with the plug out. This is where the heat goes, in the order that matters, and what it costs to stop each one.
The short answer
In most Australian homes the heat leaves through the ceiling first and through gaps second. Those two are also the cheapest to fix, which is why they are always the place to start. The floor is next if your house is up on stumps. Walls and windows lose plenty too. They just cost far more for each bit of heat you save. So they belong later, unless other work has already opened them up.
The one to check first
Get a photo of your ceiling insulation. Flattened, gappy or missing is the most common thing we hear about, and the most worth fixing.
The cheap one
Draught sealing costs a fraction of insulation and is felt the same evening. It is the best value job in the whole house.
The trap
Do not seal a house tight without a plan for fresh air. Warmth stays in and so does moisture. Our ventilation guide covers what to do.
Where it goes, in order
Heat goes up, and it goes out through holes.
Warm air rises. In a house that means the ceiling is doing most of the losing, all winter, every winter. It is also the easiest surface in the building to get to, because there is usually a hatch and a crawl space above it. Cheapest to fix, biggest effect. That is why it is always first.
Second is gaps, and gaps are strange because they are invisible and they add up. Around doors and windows, under skirting boards, around exhaust fans, through unsealed downlights, and straight up an open chimney. Individually each one is nothing. Together, in an older house, they can add up to leaving a window open all winter.
Then the floor, if there is a space under it. Then the walls. Then the windows. Every one of those is real heat loss. Every one of them also costs a lot more per bit of heat saved than the first two. That is the entire ranking, and it is why almost every honest assessor tells you the same thing.
How to feel it yourself
On a cold windy evening, hold the back of your hand near the bottom of an outside door. Then around a window frame. Then near a downlight. The back of your hand picks up moving air far better than your palm does. Make a list as you go.
The five jobs
What each one does, and what it takes.
Ceiling insulation
Batts or blown in material laid across the ceiling. The best value insulation job in an Australian house by a wide margin. If yours is there but flattened, thin, or has gaps where somebody has walked, a top up is often enough rather than a full replacement.
Why it comes here
Biggest single loss, easiest access, largest available help from government schemes.
Who does it
An insulation installer who will go up, photograph what is there now, and show you before quoting.
Up to $1,500
VictoriaVictoria offers a ceiling insulation discount to all eligible homes under its energy upgrades program. That amount is for an average Melbourne home, and up to $2,100 in colder regional areas. Other states run their own programs on their own terms.
Draught and weather sealing
Brush seals on doors, sealing around window frames, covers on unused wall vents, sealed exhaust fans, and something across an open fireplace. Usually a day of work or less and the cheapest line on this page.
Why it comes here
Cheapest fix in the house and the one you feel the same evening. Also what makes a heater smaller.
Who does it
A draught proofing specialist, who uses a smoke pencil to find the leaks.
Underfloor insulation
Only relevant if your house is on stumps or piers with a crawl space. Batts or boards fixed up between the floor joists. It makes a real difference to how a timber floor feels underfoot, which is a comfort win as much as a bill one.
Why it comes here
Genuinely worthwhile in a raised house. Irrelevant on a concrete slab.
Who does it
An insulation installer who does subfloor work. Access is the thing that decides the price.
Wall insulation
Blown in through small holes from outside, or fitted from the inside when a room is being renovated. It works, and it costs a lot more per unit of heat than the ceiling does. Our honest advice is to do it when the walls are already open for something else.
Why it comes here
Real, but expensive per unit of heat saved. Best value when it rides along with other work.
Who does it
A specialist installer. Ask specifically what your wall construction is before anybody quotes.
Windows
The most expensive way to fix a cold house and sometimes the only way, especially in a room with a lot of glass. There are three quite different price brackets here and they solve the same problem in very different ways.
Why it comes here
Big loss, big cost, and the rebates are small compared to the job. Worth a guide of its own.
Who does it
A glazier or a secondary glazing specialist.
What R value means
Bigger number, slower heat.
Insulation is sold by its R value, and all it means is how much the material slows heat down. R2.5 slows it more than R1.5. R5.0 slows it more again. That is the whole idea.
Two things trip people up. The first is that gaps beat R value. A neatly laid R2.5 ceiling beats a patchy R5.0 one. Heat takes the easy route, and a gap is the easy route. Coverage matters more than the number on the bag.
The second is that the right number depends on where you live. A house in Hobart and a house in Cairns want very different ceilings. A Victorian rental has a set figure written into the rules it must meet from March 2027. Ask your installer what is right for your climate rather than buying the highest number on the shelf.
Where this comes fromconsumer.vic.gov.au, checked 6 October 2026
If you rent it out
In Victoria, two of these stop being optional.
If you own a rental in Victoria, insulation and sealing are moving from a good idea to a requirement. From 1 March 2027 rentals need a set standard of ceiling insulation, along with four star showerheads and cooling in the main living area. From 1 July 2027, draught sealing to external doors, windows and wall vents is added.
Those two dates are law rather than a forecast, and they apply in Victoria only. If you own a rental elsewhere it is still worth knowing. It shows which way the rules are heading. The work pays for itself in a tenant’s bills either way.
If you are a tenant, two things need nobody’s permission. Seal your own doors with a brush seal that peels off, and block an unused fireplace. Both come out again when you leave.
Where this comes fromconsumer.vic.gov.au, checked 6 October 2026consumer.vic.gov.au, checked 6 October 2026
What we couldn’t confirm
The percentages we would not print.
Insulation marketing is full of very precise sounding percentages. Here is what we could not put a source behind.
“You lose 35% of your heat through the ceiling”
The share depends on the house, its shape, its age and its climate. The ceiling is the biggest single loss in most Australian homes, which is the part we are confident saying.
“Insulation pays for itself in two years”
It depends on what you are heating with, how much you heat, and what you paid. It is usually one of the fastest paybacks in the house. We will not attach a number to that.
A national insulation rebate
There is no federal program. Several states run their own with different amounts and rules, and Victoria’s opens up in October 2026.
Quick answers
The questions people ask next.
How do I know if I already have ceiling insulation?
Look through the manhole with a torch, or ask an installer to photograph it. You want to see even coverage right out to the edges with no bare patches and nothing squashed flat.
Can I lay insulation myself?
Physically yes, and people do. The risks are downlights, wiring and heat, and getting the coverage even in the awkward corners is harder than it looks. If the roof space is tight or the wiring is old, pay somebody.
Does insulation help in summer?
Yes, and in many parts of Australia that is the bigger win. A well insulated ceiling keeps a hot roof cavity out of your rooms all afternoon.
What about foil or reflective insulation?
It works differently. It reflects radiant heat rather than slowing conduction, so it is more useful against summer heat than winter loss. It is not a replacement for batts, it is a different tool.
Do I need to take the old insulation out?
Usually not. Topping up over the existing layer is normal and cheaper. It comes out if it is wet, mouldy, contaminated, or if it is one of the older materials an installer flags on the day.
Will sealing the house make it stuffy?
It can, and that is the real trade off. Sealing keeps warmth in and keeps moisture in with it. Do the sealing, and read the ventilation guide at the same time rather than a year later.
What to do this week
Free things, in order.
Tonight
The back of the hand test on a windy evening. Doors, windows, downlights, wall vents, fireplace. Write the list down.
This week
Get a photo of your roof space. Yours, or somebody else’s phone. Look for even coverage and no bare patches.
Before quoting
Find out whether your house is on a slab or on stumps. It decides whether underfloor is even on your list.
When you’re ready for help
Find the right help for your next step.
Get a whole-home plan
A home energy assessor can look at your whole home, identify the biggest opportunities and help you work out what to tackle first to make it more comfortable, efficient and cheaper to run.
Find an assessor near youFind the right specialist
Once you know which upgrade you need, find a business that specialises in that type of work and services your area.
Find a specialist near youKeep reading
