Sheet 03System types

Physical and chemical termite barriers

A physical barrier is a material termites cannot get through, such as stainless steel mesh or graded stone: it either keeps them out or makes them build their shelter tubes where they can be seen. A chemical barrier is an unbroken band of soil treated with a termiticide that termites cannot cross. QBCC’s booklet puts the difference in time: physical systems are generally designed to last the lifetime of the building with proper maintenance, while chemical systems have a limited life and need ongoing treatment.

General information, not building advice. The official places to check are the code and QBCC’s booklet, linked at the foot of this page, with your builder and building certifier.

The code’s words

Sheet, granular, chemical

The code’s Table 3.4.2 does not name products. For a slab’s perimeter it lists slab edge exposure, sheet material, granular material and chemical. Queensland’s version of the table is more literal, with columns for termite shielding, stainless steel mesh, graded stone and chemicals.

CSIRO’s guide gives the physical family in full: ant caps on stumps, metal strip sheeting for masonry walls, rigid PVC or metal collars sealing pipes that pass through a slab, fine stainless steel mesh at penetrations, joins and the perimeter, and graded crushed rock that termites cannot get through.

Four sections

Four ways to draw the line

Graded stoneCompacted rock particles 1.7–2.4 mm across, so termites can neither crawl between them nor move them, as Queensland’s fact sheet describes. QBCC adds that the granite particles are too hard to eat, and can go under the whole slab, around stumps, around the perimeter or around single penetrations.
Stainless steel meshFinely woven, high-grade stainless steel, laid under the whole slab, around the perimeter as a partial barrier, or around single penetrations. The manufacturer maintains that its grid is fine enough to keep termites out and strong enough that they cannot chew through, and QBCC notes that, being stainless, it is unlikely to be affected by corrosive concrete and ground conditions.
Chemical beneath the slabA reticulation system, a network of perforated pipes in CSIRO’s description, has to go under the slab before the concrete is poured, QBCC says, and lets the chemical be recharged from outside the building. CSIRO’s guide says treating the soil once, before the membrane and slab go down, will not on its own meet the code’s requirements.
Chemical around the perimeterUsually a trench dug around the slab or supports and backfilled with treated soil, in CSIRO’s description; under areas that will be paved, a reticulation system should go in; otherwise problem areas have to be drilled so insecticide can be injected into the soil below. Queensland adds a concrete cover strip over the trench (Sheet 01).

The four drawings are diagrams, not construction details, and they are not to scale.

Weak points

Where each one is weakest

From QBCC’s booklet, CSIRO’s guide and the Victorian Building Authority, as noted in each cell.
Question	Physical	Chemical
Pipes through the slab	Only the area around each penetration needs protecting (QBCC).	If chemical protects the penetrations in a concrete floor, the whole under-slab area must be treated (QBCC).
The ground	A well-built slab on prepared ground is a very effective barrier, but cracks as small as 1.5 mm may let termites into wall cavities and under floors (VBA).	Sandy loam suits; crusher dust, stone and rubble do not, and contractors need to check the soil before applying anything (QBCC).
What wears it down	Being bridged: garden beds or wood chips built up to the house, or unprotected carports, pergolas and fences attached to it (QBCC).	Renovations, garden alterations, slab movement and the insecticide running down over time, all among the things CSIRO lists as affecting a barrier’s integrity.

Water is the shared risk. After floods in Queensland, a guide hosted by QBCC lists all chemical barriers, and physical ones such as stainless steel mesh and graded stone, among the systems likely to have been compromised by water, silt and mud.

In between

Combinations, and the options in between

Many houses need more than one line. QBCC names split-level and zero-lot-line buildings as two examples that call for physical systems or termite-resistant materials, and warns that a chemical system alone may not be enough in some cases.

Some products sit between the two families. CSIRO describes flexible plastic sheets carrying a termite-specific insecticide, such as deltamethrin or bifenthrin, built in as a barrier, with insecticide sealants or beads filling small gaps. It calls spraying a finished frame with insecticide not ideal: penetration is limited, not every surface can be reached, and the face of the bottom plate on the slab, a prime access point, will usually go unprotected.

Baits are a different tool. Victoria’s health department explains that baits do not isolate a building, since termites can still reach it, and that barriers are preferred for long-term structural protection; it calls physical barriers the least toxic method for new buildings. The chemicals themselves have a sheet of their own.

Whichever line is drawn, QBCC makes the same point about all of them: properly installed and maintained systems impede and discourage concealed entry, but they do not always stop termites coming in the open. Whatever the system, QBCC says regular inspections by a licensed contractor are what make sure termites have not bridged the barrier. Sheet 05 covers that upkeep.