How termites get into a house: the routes they actually use
Termites do not break into a house. They find a gap that is already there, cover it over, and walk in where nobody can see them.
Where do termites come from before they get in?
Subterranean termites (the group that damages Australian houses) enter from the soil, under cover, through a gap they did not have to make. The nest is normally outside the building: in or under a stump, a living tree, a retaining wall, a fence post, a pile of buried timber or simply in the ground. Workers travel out from it through soil and through galleries they build. They avoid open air wherever they can, because exposure dries them out and exposes them to ants.
That single behaviour explains every route below. Termites are not looking for a weakness in your house. They are looking for a continuous, humid, covered path from soil to timber: and a building gives them a lot of those for free.
The routes, and where each one shows
| Route | Where to look | Why it stays hidden |
|---|---|---|
| Cracks and joints in a concrete slab | Along the slab edge, at construction and control joints | The gap is inside the slab, under the floor covering |
| Service penetrations | Around pipes, conduit and drains where they pass through the slab | Boxed in, tiled over, or inside a wall cavity |
| The cavity in a brick wall | Weep holes and the base of the cavity | The run is between the two skins of the wall |
| Piers, stumps and steel supports | Subfloor: mud tubes up a pier to the bearer | Nobody goes under the house |
| Timber touching the ground | Steps, deck posts, pergola posts, fence lines running to the house | Contact point is at or below soil level |
| Fill built up against the wall | Garden beds, mulch, paving, paths, rendered slab edges | It covers the one strip that was meant to stay visible |
Can termites get through a concrete slab?
Not by eating it, and not by boring through sound concrete. They use what is already there. A slab shrinks and cracks as it cures, it has construction and control joints by design. And it is penetrated wherever a water pipe, a waste pipe or an electrical conduit comes up through it. Any of those can be wide enough for a worker to pass, and once it is inside, it is under your floor covering and out of sight.
This is why the exposed slab edge matters so much on a slab-on-ground house. That strip of visible concrete between the finished ground level and the bottom of the wall is not decoration. It is the inspection zone, the place where a mud tube coming out of the ground has to break cover and be seen. Render it, tile it, pave over it or bank a garden bed against it and you have not stopped anything. You have removed the only place the evidence was going to appear.
Houses on stumps: the subfloor route
A suspended timber floor gives a much more direct path: soil, then a pier or stump, then a bearer, then the floor. Termites will not cross the exposed surface of a pier in the open, so they build a mud tube up it. That is why the subfloor is the highest-yield place to look in this style of house.
Ant caps on the top of the stumps do not block them either. A cap is designed to force the tube out and around its lip, where it becomes visible to whoever is looking. It is a detection device, not a barrier.
Stored timber under the house, damp ground and blocked vents all make the same subfloor far more attractive; moisture, subfloors and ventilation covers what to change.
Bridging: how a working barrier stops working
New Australian houses are generally built with a termite management system under the National Construction Code (a physical barrier, a treated zone, or a combination). The details of what was installed should be recorded on a durable notice in the building.
None of it is a force field. Every one of these systems works by making termites either stop or show themselves at a defined line. And every one of them is defeated the same way: by something being built, planted or piled over that line afterwards.
The usual culprits are garden beds and mulch raised against the wall, a new path or paving laid at or above the slab edge, a deck or a planter box attached to the house. And render carried down over the slab edge. Fill left against the wall after landscaping does it too. Physical barriers and termite mesh explains what each type is actually doing and where the line is meant to sit.
The routes that do not start in the soil
Three exceptions are worth knowing, because they change what applies to you:
- Drywood termites do not need soil contact at all. They fly in and start a small colony inside the timber itself, which means soil barriers are irrelevant to them. They are a much smaller problem in Australia than subterranean species, and they behave differently: see the Australian termite species that matter.
- Nests above ground. A colony established in a tree, a stump or occasionally in the building itself can run galleries into the structure from above or beside rather than up from the ground.
- Timber brought in. Firewood stacked against the house, second-hand sleepers, recycled timber and untreated offcuts left under the floor can all arrive with an infestation, or simply give a passing colony a reason to stay.
What this means when you look at your own house
Every route above is concealed by design, which means what you can see is only the last few centimetres of it. Two practical consequences follow. Keep the inspection zones visible (the slab edge, the subfloor, the perimeter strip against the wall), because they are not maintenance oversights. They are the way the system is meant to work. And treat anything you find on one of those zones as the tip of a route, not the problem itself.
If you do find a tube, a crust of mud or a hollow-sounding board, leave it exactly where it is, photograph it. And book an inspection carried out to AS 4349.3. Breaking a tube open or spraying the point where it comes out makes the colony abandon that route and re-enter somewhere concealed. The damage continues, and now nobody can follow it back. Checking for termites yourself is the walk-around that finds these things without touching them.
Frequently asked questions
Can termites come in through the roof?
Reaching roof timbers is common; arriving there from the sky is not. Subterranean termites that turn up in a roof void have almost always travelled to it from the ground through a wall cavity or from a nest in a nearby tree, and mud staining on the top plates is the trace of that journey. The entry point is still down at soil level, which is where the work has to be done.
My house is on a concrete slab. Does that make it safe?
No. A slab removes the easy subfloor route and replaces it with a concealed one. Termites use shrinkage cracks, construction joints and the gaps around pipe and conduit penetrations, and once they are through, they are under the floor covering rather than under the house where you could have seen them. Slab houses are not lower risk, they are harder to inspect.
If I seal the cracks and the weep holes, will that keep them out?
Sealing weep holes is actively harmful: they drain and ventilate the wall cavity, and blocking them creates the damp conditions termites prefer. Sealing visible cracks does not work either, because the route is inside the slab and the wall where you cannot reach it. What does help is keeping the inspection zones clear and having the house inspected on a regular cycle.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Queensland Building and Construction Commission. Protect against termites — termite management systems and inspections
- Australian Building Codes Board. National Construction Code
- Standards Australia. Australian Standards (AS 3660 termite management, AS 4349.3 timber pest inspection)