Bridging (termite barrier)

Bridging is the termite barrier failure mode where soil, mulch, render, paving, or another material sits above the level of the installed barrier and provides a concealed entry path for termites past the barrier and into the building. AS 3660.1 and AS 3660.2 both treat bridging as the single biggest failure mode of an otherwise well-installed termite system. Bridging is builder-caused 90% of the time: well-meaning landscaping, render finishes, garden bed buildup, or paving placement defeats the chemical or physical barrier that cost the build $3,000-$5,000 to install correctly.

Why bridging is a critical concept for builders:

A chemical barrier under a slab, or a physical barrier (Termimesh, Kordon) at the slab perimeter, is only effective if termites cannot pass over it concealed. AS 3660.1 requires an inspection zone of typically 75-100 mm clear visible perimeter below the slab edge. If anything fills that inspection zone, termites can enter behind it without leaving a visible mud tube.

Common bridging scenarios:

Cause	Where	Severity
Garden bed soil heaped against external wall	Side and rear elevations	Very common
Mulch piled too high	Garden beds against the wall	Very common
Render carried below the inspection zone	Architectural finish that wraps to the slab edge	Common; once installed, expensive to fix
Paving or concrete path sloping toward the wall with no gap	Driveway, side path, alfresco area	Common
Retaining wall built against the building with backfill above slab edge	Sloping site	Common
Step or stair built up to the wall	Patio, deck, alfresco	Common
Air conditioner condenser pad poured against the slab	Side wall	Less common but easy to miss
Soil from new turf or landscaping installed after handover	Builder-handed-over OK, client landscaped poorly	Very common post-handover

How to identify bridging:

Walk every external wall and check the height of soil, mulch, paving, render finish at the wall-to-ground junction.
AS 3660 requires a clear visible inspection zone of typically 75-100 mm (75 mm minimum; 100 mm preferred for visibility).
Look for capillary breaks: paving or path should slope away from the building, with a clear gap (typically 75 mm + drip edge).
Garden beds: organic mulch should be no closer than 75 mm from the slab edge, capped at the inspection zone level.

Consequences of bridging:

Voids the manufacturer warranty on most chemical and physical barriers (Termidor, Kordon etc. specifically exclude bridging-caused failure).
Termites enter concealed: by the time mud tubes are visible, structural damage may be widespread.
Insurance complications: building insurance does NOT cover termite damage in Australia (standard exclusion). Bridging-caused termite damage is uninsurable.

Remediation:

Bridging cause	Remediation
Soil/mulch buildup	Excavate down to 75 mm below slab edge; replace with inorganic mulch or gravel
Render below inspection zone	Cut back the render to 75 mm above slab edge; expose the inspection strip
Paving too close	Saw-cut paving to create a 75 mm inspection gap; install drainage
Retaining wall too high	Re-level fill; install a separate retaining wall with a gap
Step/stair against wall	Re-detail with a gap or moisture barrier

Render bridging is usually the most expensive to fix because it requires cutting masonry render and re-rendering with a clear line.

For builders:

Brief the chippy, brickie, landscaper, and concretor at engagement that 75 mm of clear inspection zone must remain visible at the slab perimeter at handover.
Walk the perimeter at PCI specifically looking for bridging. Fix anything that violates the 75 mm rule before handover.
Hand the client a written warning at handover not to garden, mulch, render, or pave within 75 mm of the slab edge. Note that bridging voids the termite warranty.
Photograph the inspection zone at handover and store with the durable notice.

Also known as: termite bridging, barrier bridging, bridge over termite barrier.

Category: Termite / failure modes / AS 3660.

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