Ceiling Insulation or Draught Sealing: Which Fixes a Cold Melbourne Home First?

If a Melbourne home is still cold in August with the heater running, there are usually two separate things going on: heat leaving through the ceiling, and air leaking in and out around the edges of the building. They feel similar from the couch, but they are different problems with different fixes — and doing them in the wrong order wastes money.

What each one actually does

Ceiling insulation slows heat moving through a solid surface. Warm air rises, sits against the plaster, and the heat in it works its way up into the roof cavity and out through the tiles. A properly installed layer of insulation puts a barrier of trapped still air in the way, so that transfer happens far more slowly.

Draught sealing does something different. It stops whole parcels of air physically moving between inside and outside — under the front door, around an old wall vent, through the gap where pipes pass into the roof, around an unsealed exhaust fan. Air that leaves carries its heat with it, and cold air pulled in to replace it has to be heated from scratch.

The distinction matters because insulation cannot do anything about air that simply goes around it. A ceiling can be perfectly insulated and still bleed warmth all night through a dozen unsealed penetrations.

How to tell which problem you have

Draughts announce themselves at ankle height and near openings. On a windy Melbourne evening you can often feel them directly: a cold stream along the hallway floor, a curtain that moves with the doors shut, a room that feels colder whenever the wind swings around to the south. Draughts also tend to be worse on windy days than on still ones, which is a useful tell.

Insulation problems feel different. The room is not draughty, it simply will not hold heat. The heater brings it up to temperature, and half an hour after it switches off the warmth has gone. One room — often an extension, or a room under a lower section of roof — stays colder than everywhere else no matter what you do. Ceilings feel cold to the touch, and in some homes you can see faint darker lines on the plaster where dust has settled along the cooler gaps between batts.

The two also differ in timing. A draughty house feels cold the moment the wind picks up. A poorly insulated house feels cold every single night regardless of weather.

Why draught sealing usually comes first

Sealing is generally the first move, for three practical reasons.

It is less disruptive. Most of the work happens inside the house or at the ceiling surface, not in the roof cavity.

It is immediate. A sealed door and a set of sealed penetrations change how a room feels the same evening.

And critically, it protects the investment in insulation. Air leaking up through ceiling penetrations does not just remove heat — it moves through and around the insulation layer, and over years it drags dust up into the batts and can leave them grubby and displaced. Sealing first means the insulation you add afterwards works in still conditions, which is what it was designed for.

Where the leaks hide in a typical Melbourne home

The specific culprits repeat from house to house.

Unsealed downlights. Older recessed fittings often sit in an open hole in the plaster, and the batts have to be held back from them for heat clearance. Each one is a permanent chimney from the room into the roof space.

Exhaust fans that vent into the roof. A fan with no duct to outside is both an air leak and a moisture problem, dumping shower steam straight into the cavity.

The manhole. A plain sheet of plaster resting in a frame leaks continuously unless it has been weatherstripped.

Old wall vents. Common in period homes, and often left in place long after the appliance they ventilated was removed.

Door undercuts and gaps. Especially the door between the house and an unheated garage or laundry.

Service penetrations. Anywhere plumbing, wiring or a heating duct passes through the ceiling or an external wall.

What checking the ceiling insulation involves

Once the obvious leaks are sealed, the ceiling itself is worth a proper look rather than a guess. An inspection from the manhole tells you very little, because the area near the access point is almost always the tidiest part of the roof space.

The things that matter are coverage and condition. Coverage means whether the layer is continuous — batts pushed aside by an electrician or an antenna installer leave direct paths for heat, and gaps at the edges where the roof meets the wall are extremely common because the space is awkward to reach. Condition means whether the material is still doing its job: batts that have been compressed by foot traffic or storage have lost much of their thickness, and loose-fill that has settled or been disturbed no longer sits at an even depth.

It is also worth noting what is above the insulation. Homes without sarking under the tiles get more dust and wind-driven grit into the cavity, and that gradually works into the top of the batts.

Doing them in the right order

For most homes the sequence that makes sense is: seal the uncontrolled leaks, keep the deliberate ventilation, then assess the ceiling insulation with the draughts already out of the picture. Doing it that way means the insulation is judged on its own merits, and you are not paying to insulate a ceiling that is being ventilated by a dozen small holes.

There is one caveat. Sealing a house tightens it, and a tight house needs its moisture managed deliberately — extraction fans that vent outside and get used, and a dryer that is vented properly rather than into the laundry. Late winter in Melbourne is exactly when that moisture load is at its heaviest, so the two jobs belong in the same conversation.

Frequently asked questions

Should I seal draughts before adding ceiling insulation?

In most Melbourne homes, yes. Draughts move air, and moving air carries heat with it — so a leaky ceiling penetration or an unsealed door undercut will keep stealing warmth no matter how much insulation sits above the plaster. Sealing is also the cheaper and less disruptive of the two, so it makes sense to do it first and then judge how much of the cold is left.

How can I tell if my ceiling insulation has stopped working?

The common signs are rooms that lose heat quickly after the heater goes off, one room that is noticeably colder than the rest, cold patches or shadowing on the ceiling, and a roof space that feels the same temperature as the rooms below. Batts that have been walked on, pushed aside by trades, or flattened over time lose much of their effect even though they still look present from the manhole.

Does draught sealing cause condensation or mould problems?

It can if it is done without any thought for ventilation. A home still needs a way to shift moisture from showers, cooking and drying clothes. The usual approach is to seal the uncontrolled leaks — gaps around penetrations, unsealed downlights, door undercuts — while keeping deliberate ventilation such as exhaust fans that actually vent outside, and using them.

Is late winter a sensible time to look at insulation?

It is a practical time, because you can still feel exactly which rooms are underperforming, and the roof space is cool enough to work in safely. Waiting until summer means diagnosing a winter problem from memory, and roof cavities become genuinely dangerous to enter on hot days.