Subterranean termite infestation in buildings

B.C. Peters, J. King and F.R. Wylie

Strategies used to protect buildings and other structures from subterranean termite infestation in Australia are prevention (keeping termites out) and cure (eliminating infestations).

Requirements for the prevention, detection and treatment of subterranean termite infestation in buildings, including methods for the prevention of reinfestation are specified in the Australian Standard AS 3660 series. This series is an amalgamation and revision of previous documents, Australian Standards AS 1694, AS 2057 and AS 2178 and is available from Standards Australia. Curative measures usually involve the use of chemicals including dust applications, edible bait toxicants and soil insecticides.

The prevention and treatment of subterranean termite infestations in buildings in Queensland are discussed in this DPI&F Note. Methods which may be used to reduce the incidence of subterranean termite damage in buildings are also discussed.

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. Information on these provisions for NEW BUILDINGS can be found at: www.lgp.qld.gov.au/docs/corporate/publications/building_codes/newsflash/2000/073.pdf ( PDF, 114kB)

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.

In rare cases, a nest may be established inside the building as an offshoot from an existing colony, or by mated pairs following a swarming flight. Such nest establishment can occur where a source of permanent moisture and food is available to the termites within the building (for example, leaking plumbing) and in this situation there may be no contact between nest and soil. In most cases entry of a building by winged subterranean termites does not result in colony establishment because moist, partially-decayed timber is not available. Subterranean termites cannot establish a nest in a house from infested firewood or other material brought into the house because connection with the central nest has been broken.

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 by the owner (at three to four month intervals) for signs of termite activity will reduce the danger of serious infestation occurring.

A competent inspector should have access to a range of devices to assist in the detection of termite activity. Such devices include a screwdriver, small knife, moisture meter, borescope and microwave technology instruments (which can detect movement within timber). For many situations, a bright light is essential, and where necessary, overalls, respirators and other protective equipment should be used. The parts of the building in contact with or close to the soil should be inspected first. Locations where dampness or humid conditions prevail, such as bathrooms, laundries or places where there are leaky pipes or drains are likely places of infestation. The presence of galleries is a common indicator of a termite infestation. Termite damage in timber may be detected by the presence of mud 'plastering' along joints and cracks in the surface. Where termites are working between timber walls or in timber that has been painted, there may be noticeable bulging, staining or rippling of the surface. Similarly, infestation in the wall cavity of a brick veneer house may result in an area of stained plaster veneer. Damaged wood, when lightly tapped, often has a 'papery' sound. Timbers with a large cross section, such as house stumps, may have to be drilled or probed to determine their condition. Places to look for termite mud galleries or damage include building foundations, piers or stumps and sub-floor area, skirting boards, architraves, cornices, mouldings and roof timbers, particularly those made of softwood. Note that drilling timber which is not infested with termites and treatment with termiticidal emulsion will not prevent infestation.

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.

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 (Figure 1), 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 (Figure 2). 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 (Figure 3).

Stumps can be protected in-ground by graded stone barriers (Figure 4). 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.


Figure 1. Physical barrier (termite shield) bridged by subterranean termites	Figure 2. For suspended timber floors, termite shields and routine inspections provide adequate protection.

Figure 3. Stainless steel mesh can be used to provide physical barriers.	Figure 4. Graded stone barriers consist of compacted rock particles.
	Figure 5. With slab-on-ground construction, many areas are inaccessible for inspection.

Modern building practices, such as those involving slab-on-ground construction (Figure 5), 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

Integrated termite management techniques using a range of complementary methods, including improved building design, wood preservative treatments, physical barriers and dust toxicants, can be used successfully to prevent termite infestation, while minimising reliance on chemical sprays and drenches. The method chosen will depend on the type of building and individual preference. Some options for each type of construction are given in Australian Standard AS 3660. Procedures from two or more options can be combined to give a higher level of protection.

Treatment of active infestation

After the discovery of an active infestation, it is important that the termite workings are not further disturbed until the management approach has been determined (see Precaution ). Several techniques for the management of active termite infestations are described in Australian Standard AS 3660. No single treatment technique will necessarily be successful in all circumstances, and sometimes a combination of methods is required. Choice of treatment will be influenced by factors such as soil type, topography, building design and relationship to neighbouring structures. It is prudent to seek professional advice in determining the most appropriate approach.

Destroying the nest

Considerable emphasis is sometimes placed on locating and destroying the nest from which the infestation originates. This approach is valid provided an identification check is made to ensure that the species of termite in the building is the same as that in the nest to be destroyed. Many mound-building and tree-nesting termites occurring in urban areas do not infest sound seasoned timber. Destruction of the nest does not protect the building from infestation by other colonies and regular inspection of the building is essential. Nests in tree trunks can be drilled and treated with a termiticidal emulsion, if considered necessary.

Destroying the colony with toxic dust

Toxic dust can be used to destroy a termite colony even when the nest has not been located (Figure 6). The treatment can be carried out only by an experienced operator licensed to obtain and use either of the dusts.

Photo of toxic dust being applied

Figure 6. Toxic dust can be used to destroy the termite colony.

The fine, dry dust (usually arsenic trioxide or triflumaron) is blown into occupied galleries by means of a hand blower. The dust adheres to the bodies of passing termites and is distributed into the colony. Arsenical dusting is ineffective against some species of termite, for example Coptotermes frenchi , which tend to avoid disturbed areas. Alternatively, termites may be aggregated using susceptible timber, removed, dusted and then returned to the site of activity. Boxes, containing corrugated cardboard and susceptible timber, placed in the soil near termite activity can facilitate aggregation. For these methods to be effective and safe, operator skill is required in judging the quantities and placement of dust and in handling the poison.