Isolate from Pests – from Forest and Wood Products Research and Development Corporation

Topics Covered

Background

Barriers

Background

In terms of strategies to protect timber from degradation, isolating all timber and wood fibre in a building from biological hazards is one of the most effective.

Australia's size and diverse climate presents timber designers and builders with some unique problems. In the hottest part of the country we have one of the world's most voracious termites, Mastotermes darwiniensis, and elsewhere there are other termites. Australia also has a range of wood destroying fungi. In other environments our timbers may also be attacked by marine borers and wood boring insects, such as lyctids and anobiids.

In areas where termites are active, total building protection against termite infestation is the only way to minimise the risk to the structure, non structural elements and contents. This is achieved by putting barriers between the soil and the structure that will prevent termites from gaining unseen access to the structure. This will force any termites that try to enter the structure to adopt a path where their presence will be seen.

Isolation from termites requires a combination of passive measures and active measures. It can be achieved by:

appropriate design and construction –

• all timber in contact with the ground must be termite resistant
• incorporate physical barriers such as ant-caps, “termimesh” or “granitguard” that prevent termites gaining access to the structure directly from the ground
• eliminate the presence or trapping of moisture and provide adequate ventilation to enable timber to remain dry (termites are more attracted to damp timber)
• services (pipes, plumbing, wiring) should be installed so that they do not penetrate through slabs or footings or if they do, the penetration should be protected with “termimesh”
• ensure crawl spaces permit inspection of termite barriers and sub-floor timbers and they have adequate clearance and ventilation
• cavity or hollow masonry should be avoided below ground level

care during site preparation – ensure building sites and under buildings are clear of debris, trees, and organic matter. Engage a licensed pest controller to treat any nest or colony that may be present.

adoption of appropriate construction practices –

• eliminate/minimise cracks in concrete foundations and slabs using appropriate reinforcement, overlaps in reinforcement sheets, and concrete of the correct consistency (over-wet concrete is more likely to develop shrinkage cracks)
• remove all timber formwork, form boards, profiles, pegs etc near or under foundations or slabs.
• Install appropriate physical or chemical barriers with attention to detail at joins, corners and slab penetrations or junctions (infill slabs completed at the end of the job often escape the appropriate diligence in detailing
• Ensure physical barriers are not damaged by other trades people (especially in the installation of plumbing)
• Ensure weep holes in brickwork are not covered by soil or other landscaping materials
• Once formed, any barrier should not be bridged by construction eg carports or landscaping, or breached by installation of underground services. Action must be taken to maintain or restore the barrier system.

• ongoing inspection and maintenance – regular inspections will involve looking for places in which the termite barrier has been bridged by plants or buildings, or penetrated. Where the barrier is effective, termites must move into the open to get around it. They create a bridge using a mud gallery or tunnel. This enablesthem to move around the edge of the barrier without exposure to sunlight. Inspections will check for signs that termites have gained entry to the building by making galleries around the barriers. If this is the case, the infestation killed by application of chemicals.

Barriers

Barriers are passive measures that force the termites into the open, if they try to go around the barriers. Once in the open, their passage can be seen in an inspection. Different types of structural systems require different types of barriers

Suspended timber floors

The most traditional way of resisting termite infestation with suspended timber floors is by the use of ant caps or termite shields combined with periodic inspections of the sub-floor space for signs of termite activity. Other chemical and physical barriers can also be used alone or in combination with these measures. These options include chemical barriers around posts, stumps and strip footings as well as crushed granite or stainless steel mesh.

Buildings with suspended timber floors should be designed to ensure a physical barrier is easily installed between the lowest timber floor and the ground. This also applies to stairs, pergolas and decks.

Support posts, poles and stumps should be made from termite resistant or timber treated to H5, steel stumps and brackets or continuous concrete stumps/footings.

Ant caps – are formed from galvanised sheet metal or stainless steel mesh, and are inserted between the lower floor framing timbers and the supporting stumps, piers or masonry bases. They are designed to force termites out into the open, as in order to gain access to the timber above, they must go around the edge of the steel ant cap.  This will require the construction of an exposed mud gallery that will be detected during a routine inspection.

Sufficient under floor crawl space (400mm clearance to the underside of the bearer) should be provided to enable easy access and inspection of physical barriers.

Slab on ground construction

A range of chemical and physical barrier systems can be used to provide termite protection for slab on ground construction. Most physical barrier systems prevent access to the building by pests the size of termites:

• Monolithic slabs – The unbroken slab from edge to edge provides a significant barrier. There should be no cracks or construction joints. Any slab penetrations such as plumbing, must be surrounded by a close fitting collar that is cast into the concrete to prevent termite ingress between the pipe and the concrete. The edges of these slabs that are permanently exposed to view can also provide for physical inspection and detection.
• Stainless steel Mesh barriers – (‘TermiMesh’) consist of a fine woven marine grade stainless steel mesh. The mesh is too small for them to pass through and too tough for them to chew through. Where there are discontinuities in the slab (for example where the footings are not integral with the slab), stainless steel mesh can be used to prevent termite access. The mesh is cast into the concrete on each side of the discontinuity. Similar techniques can be used at pipe penetrations through the slab. A tight fitting collar on the pipe links the mesh with the pipe, and the other edge of the mesh is cast into the concrete. A partial system is also commonly used, which involves the construction of a perimeter barrier only. This partial system seals the exterior brickwork to the footing and can be used in conjunction with other under slab protection systems. The mesh can also be formed into ‘socks’ for stump/post applications.
• Graded stone barriers – ‘GranitGard’) is finely crushed and accurately graded stone chips. The chips are too large for a termite to move, and leave voids that are too small for them to fit through. GranitGard can be placed around posts and footings or under the full extent of the slab, so that it will protect any crack that may open in the slab. A small recess around pipes will enable the stone to protect penetrations due to plumbing. This system is not recommended for protecting buildings against mastotermes and should only be used south of the Tropic of Capricorn.
• Chemical barriers – provide a zone of treated soil poisonous to termites either under or around footings and slabs. The most commonly used chemical, Organophosphate, degrades over time and needs to be replenished after 5-10 years. Proprietary systems such as ‘Slabset’, ‘Termguard’, ‘Altis’ etc systems overcome this problem by using a reticulated pipe network under the slab that enables chemicals to be renewed at regular intervals over the life of the building. This will ensure that the poison remains an active barrier underneath the slab, preventing termites from gaining access through cracks in the slab or gaps between the slab and plumbing. The chemicals are applied under pressure at the completion of construction by licensed pest controllers and on a scheduled basis thereafter. Where a reticulated system has not been installed, a chemical perimeter barrier can be maintained by injecting poison into the ground at close centres around the building perimeter (drilling through paving if necessary). In these cases, it can prove very difficult to inject poison under the interior of the slab.

Termite resistant timbers:

Naturally resistant timber can be used in-ground to isolate the rest of the structure from ground contact. The resistance of timber can be enhanced by chemical treatment. Natural durability of different species is listed in AS1720.2.

Source: The Forest and Wood Products Research and Development Corporation

For more information on this source please visit The Forest and Wood Products Research and Development Corporation