Moisture and the subfloor: the conditions that invite attack
Termites need moisture. Remove the water and you have done more for the house than any product will do.
Why water is the lever
Subterranean termites lose moisture through their cuticle and have to stay in a humid environment or die. That constraint shapes everything they do: it is why they build mud tubes rather than walking in the open, why they favour damp timber. And why a permanently wet patch of soil against a building is such a reliable predictor of trouble.
It is also the one part of this subject that is entirely in your hands. You cannot make your suburb less termite-prone. You can absolutely stop a downpipe discharging against a footing.
Where the water comes from
Inspection reports use the phrase conducive conditions, and moisture is nearly always the first item. The usual sources, in rough order of how often they turn up:
- A leaking tap or a leaking pipe near or under the building, keeping one patch of soil permanently wet.
- The hot water system's relief line discharging onto the ground beside the wall: it is supposed to discharge, and where it discharges to matters.
- A downpipe that ends at the footing instead of being connected to stormwater, or a blocked one overflowing at the wall.
- Air conditioner condensate dripping in the same spot all summer.
- Ground falling towards the house, so surface water runs to the wall rather than away from it.
- Over-watered garden beds against the wall, especially with drip irrigation running into a bed built up over the slab edge.
- Shower and wet-area leaks soaking wall framing from inside: a common origin for activity found in bathrooms.
If a leak is what is keeping soil or framing wet, that is a plumbing fault and it is a different trade. Our sibling site Plumbing Explained covers what sits behind a persistent damp patch and where the licensed line is.
The subfloor
Houses on stumps or piers have a subfloor, and it is where activity is found more often than anywhere else. The reason is straightforward: it is dark, it is humid, it contains bearers and joists, and almost nobody goes in there.
Ventilation is what keeps it survivable. Cross-flow through vents in the perimeter dries the space out; when that flow is blocked, humidity stays high, timber moisture content rises. And you have created ideal conditions for both termites and fungal decay. The two are regularly found together in the same subfloor for exactly this reason.
What blocks it, in practice: garden beds and paving built up over the vents, a deck or extension enclosing what used to be an open side, stored goods packed against the vents inside, and lattice or infill added for appearance. Clearance matters too. A subfloor with too little headroom cannot be inspected properly, so it will appear on the report as an area not inspected.
The other half: removing the food
Moisture brings them close; timber in contact with soil gives them a reason to stay:
- Stumps left in the ground after a tree comes out. A classic nest site.
- Timber offcuts and form-work stored or left under the house.
- Firewood stacked against a wall.
- Timber retaining walls and garden edging in soil contact.
- Old fence posts and landscaping sleepers.
None of these create termites. They give an established colony a reason to forage in your direction, and a place to build up numbers next to your building before they ever touch it.
What fixing it does and does not do
Fixing conducive conditions makes your house a less attractive target and makes inspections more useful, because the inspector can see the slab edge and get into the subfloor. It does not replace a barrier or an annual inspection. It is the layer you control, and it costs a weekend rather than a contract.
Frequently asked questions
Will fixing the moisture get rid of termites I already have?
No. An established colony needs to be dealt with directly. Fixing the moisture removes the conditions that made your building attractive and stops the next one, and it makes the treatment more likely to hold.
Is mulch really a problem?
Mulch itself is fine. Mulch piled above the slab edge against the wall is the problem, because it hides the strip of wall where a mud tube would otherwise be visible, and it holds moisture there.
My subfloor is very tight. Does that matter?
Yes, in two ways: low clearance restricts ventilation, and it restricts access, so the subfloor may end up listed in the report as an area that could not be inspected.
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
- Department of Health, Victoria. Pest control — termites