The following information, provides general information regarding:

• The prevention and treatment of subterranean termite infestations in buildings
• Methods which may be used to reduce the incidence of subterranean termite damage in buildings.

Queensland Building Act

It is a requirement of the Queensland Building Act 1975 that buildings in Queensland be constructed in accordance with the provisions of the Building Code of Australia (BCA). These provisions specify that all susceptible structural members of buildings be protected from damage by subterranean termites. If the materials and construction comply with Australian Standard AS 3660, the requirements of the BCA and the Queensland Building Act 1975 are satisfied. The use of other methods that will prevent damage to buildings by termites is also permitted in the Act. The decision to accept these preventative methods, that are not nominated in AS 3660, is at the discretion of each local council. The termite management option(s) adopted during building construction should involve some thought and consultation between the builder, local council and homeowner with regard to the method or combination of methods that best suits the situation. Factors such as durability and cost should be taken into consideration.

On 1 January 2001, the Queensland provisions of the Building Code of Australia (BCA) were amended to address the installation of termite management systems in class 1 (houses) and class 10 (sheds, garages and the like) buildings. Specifically, the provisions incorporate durability of termite management systems in NEW BUILDINGS.

How subterranean termite infestation occurs in buildings

Infestation of buildings is usually initiated from a nest in the ground from which the termites build galleries over piers or walls to infest the structure from below. Usually, the nest is outside the building perimeter, but occasionally it may be buried beneath the building in soil or fill. Termites inside the building usually maintain contact with the soil (for moisture) and with the central nest (the communications centre). Chemicals produced by the queen in the central nest are distributed throughout the colony and control its behaviour and structure.

Prevention:

Awareness of risk and regular inspection

The reason so much damage is caused by subterranean termites is that the insects usually gain entry to the timbers without being seen and are only noticed after they have been present for some time. Termite infestation is more likely to remain undetected in buildings with slab-on-ground floors than in those with suspended floors. Termite entry may occur at the slab edge, through cracks, joints and imperfections in the concrete or around service pipes. Awareness of the termite risk and regular inspections of the building for signs of termite activity will reduce the danger of serious infestation occurring.

Precaution

After the discovery of an active infestation, it is important that the termite workings are not further disturbed until management methods have been determined. Premature attempts to repair or replace infested timber may cause the termites to withdraw temporarily from the area and hinder effective treatment.

Where possible, soldier termites should be collected during the inspection, preserved in alcohol (methylated spirit is suitable) and submitted to a specialist for identification. Knowledge of the species of termite involved may affect the choice of treatment.

Elimination of conditions which favour infestation

Termite infestation is usually initiated from below the building. Poorly ventilated, poorly lit sub-floor areas increase the likelihood of successful infestation. Clearance from the ground provides an important physical barrier and also provides access for inspection. A minimum of 400 mm clearance in all subfloor areas between finished ground level and any structural component is recommended. Permanently damp areas in or beneath a building favour infestation and drainage or plumbing repairs should be effected to eliminate this source of risk.

Materials stored under buildings may promote termite entry by providing pathways around physical or chemical barriers, by reducing ventilation or by making inspection of parts of the subfloor areas difficult. Similarly, materials such as firewood should not be stored against the building for long periods. Removal or rearrangement of such materials is recommended.

Built-up gardens and shrubs close to the perimeter of the building may promote or conceal termite entry points. This is particularly so in slab-on-ground constructions. If removal or modification of these features is not possible, then careful attention should be given to these areas during inspections for termites.

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Termite resistant timbers

Several timber species possess natural properties which make the heartwood resistant to termite infestation. However, no species is totally immune. The native cypresses are the most commonly used resistant species in Queensland. Some ironbark species, for example narrow-leaved red ironbark Eucalyptus crebra and broad-leaved red ironbark E. fibrosa, as well as turpentine Syncarpia glomulifera and satinay S. hillii, are also naturally resistant to termites but unfortunately the supply of these very durable hardwoods has diminished and they are now used rarely in domestic construction. In situations where routine building maintenance is neglected, decay may predispose otherwise resistant timber to termite infestation.

Timber which has been chemically pre-treated with an approved preservative in accordance with Australian Standard AS 1604 and the Timber Utilisation and Marketing Act 1987 (TUMA) can be used to prevent or minimise termite infestation and damage.

When resistant or pre-treated timber is used in building construction, it is generally confined to structural elements such as wall and roof framing and floors. Such timber, normally, is not used in architraves, skirtings, built-in wardrobes, and other finishing applications. Therefore, considerable quantities of termite-susceptible timber will still be present.

Physical barriers

Methods employed in the erection of physical barriers during building construction are detailed in the Australian Standard AS 3660 series. These barriers impede and discourage termite entry into buildings. Termites can build around physical barriers but they can be then detected more readily during routine inspections.

For suspended floors, termite shields (caps or strip shielding) have, for many years, been placed on foundation walls, piers, stumps, and other substructures to isolate the upper parts of the building from the substructure.  Care should be exercised when enclosing the substructure area not to bridge termite shields superstructure. Stainless steel mesh can be used to provide these physical barriers.

Stumps can be protected in-ground by graded stone barriers. The graded stone barriers consist of compacted rock particles of such a size (1.7-2.4 mm in diameter) that the termites cannot crawl between them, nor move them. The technique was developed in Australia and followed work elsewhere. Stone barriers are effective in preventing penetration by Coptotermes spp. Further testing is required before a suitable particle size can be recommended for protection against other species of termite, especially the giant northern termite.

Modern building practices, such as those involving slab-on-ground construction  are not compatible with the incorporation of traditional physical barriers. The risk of termite entry into slab-on-ground constructions can be minimised by constructing slabs in accordance with Australian Standards AS 3600. The concrete can be placed, finished and cured in accordance with the procedures recommended by the Cement and Concrete Association of Australia to minimise cracks and voids.

Control joints and slab penetrations can be protected by a suitable barrier such as stainless steel mesh or graded stone. These barriers can be also installed under the whole of the slab. Exposed slab edges provide ready detection of termite entry. The vertical face of the perimeter of slabs should be permanently exposed for a minimum of 75 mm unless other barriers are installed.

Care must be taken to ensure that alterations or additions to a building, landscaping or storage of susceptible materials beneath or abutting the building do not allow termites to bypass the existing physical barriers.

Chemical barriers

The installation of a treated-soil barrier using hand-held low pressure spray equipment during building construction has been the cheapest and most effective method of preventing subterranean termite infestation. The objective of the technique was to place a barrier of chemically treated soil between the timber to be protected and the termites. Provided the barrier was continuous and not breached during subsequent soil disturbance or construction (for example, plumbing installation, landscaping or addition of carport, patio, pergola or trellis), termites were denied access for a considerable time. The highly persistent cyclodiene insecticides (aldrin, dieldrin, chlordane and heptachlor), the main termiticides used in Australia for the past 30 years, were withdrawn from use from 30 June 1995 due to the hazard they posed to human health and the environment.

Only the organophosphate chlorpyrifos, the pyrethroid bifenthrin, the chloro-nicotinyl imidacloprid, and the phenylpyrazole fipronil are now registered for use.These chemicals are much less persistent than the cyclodienes so may need to be applied more regularly if a similar level of protection is to be maintained. In the case of slabs where access is difficult, or disruptive, installation of a reticulation system before the slab is poured can facilitate repeat applications.

Integrated termite management techniques

A range of complementary methods can be used successfully to manage termite infestation. The strategy of baiting has been employed against termites in buildings and trees. The main problem with the use of baiting techniques against Coptotermes species has been the inconsistency of bait acceptance. Colonies may be destroyed by dusting termites which have been aggregated at susceptible wooden baits. Biological control using the insect pathogenic fungus Metarhizium anisopliae and the insect pathogenic roundworms (nematodes) Heterorhabdis spp. and Steinernema spp. have had some experimental success.

Other structures

The use of termite-resistant and preservative-treated timbers should be considered when new fences and landscaping timbers are to be installed. It is extremely difficult to install an effective chemical soil barrier around fence posts or behind a timber retaining wall. A 50 mm gap between the fence palings and the soil will minimise the risk of termite infestation or fungal decay and reduce the need for chemical treatment.

Summary

Subterranean termites are a hazard to timber structures in Queensland. The approach adopted in the prevention or management of subterranean termite infestation will depend on factors such as site, building design, the cost of any structural modifications, the degree of protection that is demanded and the cost of the treatment itself.

Integrated termite management techniques using a range of complementary methods, including improved building design, wood preservative treatments, bait and dust toxicants and physical barriers, can be used successfully to prevent and manage termite infestation, while minimising reliance on chemical sprays and drenches.

Reference to the appropriate Australian Standards publications will assist the building owner in making this choice.

Further reading

• Australian Standard AS 1604.1. (2000) Specification for preservative treatment - Part 1: Sawn and round timber. Standards Australia, Sydney. 44 pp.
• Australian Standard AS 3660.1. (2000) Termite management - Part 1: New building work. Standards Australia, Sydney. 72 pp.
• Australian Standard AS 3660.2. (2000) Termite management - Part 2: In and around existing buildings and structures - Guidelines. Standards Australia, Sydney. 48 pp.
• Australian Standard AS 3660.3. (2000) Termite management - Part 3: Assessment criteria for termite management systems. Standards Australia, Sydney. 32 pp.
• Hadlington, P & C. Marsden. (1998) Termites and borers: a homeowner's guide to detection and control. University of New South Wales Press, Sydney. 53 pp.
• Peters, B.C., J. King, & F.R. Wylie. (1996) Pests of Timber in Queensland. Queensland Forestry Research Institute, Department of Primary Industries, Brisbane, 175 pp. Available from Queensland Government Publications.  

Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. Redlands Pest Control has taken all reasonable steps to ensure the information is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

Last Updated January 2007.

Source of Information : Department of Primary Industries & Fisheries, Queensland Government