Preventing attack by subterranean termites
Since the time when the first white settler of Port Jackson were surprised to find their tent poles and buildings beginning to disintegrate, Australians have been trying to protect their homes against termites attack using all manner of barriers and construction methods.
Listen to any group of termite technicians discussing the extraordinary termite attacks they’ve seen and you have to wonder at the incredible perseverance termites have brought to overcoming human efforts and ingenuity to protect buildings. The following procedures and factors have each reduced the incidence of the attack. Using several methods together provides better protection. However, unforseen factors such as subsidence, add-ons, landscaping and other forms of human and animal intervention can open a 3-4mm gap for termites to get through to unprotected timber. Also, in timber framed buildings all the timber links up, so termites can move everywhere and damage the lot!
Below are several preventive methods of reducing termite attack on buildings, beginning with design (too late if the building is completed):
Design
It is possible to build structures to which termites are not attracted. Steel framing, glass and concrete/tiles without any wood has little attraction for termites although edible furniture, books and seldom moved fittings or fixtures containing cellulose could entice them.
Timber framing is now being impregnated with different low hazard insecticides, and guarantees are being offered for 20 years and more, which means the residue would last considerably longer.
A company that offers professional indemnity insurance to the pest management industry revealed that 99% of the claims they have to investigate are from the slab-on-ground construction and only 1% from buildings from suspended wooden floorings. Essentially, this is because the underfloor crawl space in the latter can be inspected and, as termites build their shelter tubes up the foundation walls, the termite presence is usually detected during a regular inspection and before extensive damage occurs.
Use of physical barriers
Buildings throughout Australia must be protected from termite attack in accordance with the standard(s). Local shires and councils may add extra requirements, however, as standards are a minimum. The names and numbers of the various standards are not listed here because they are always under review and subject to improvement and amendment in line with the development of new products and techniques.
Termite attacks almost always originate from outside a building. The installation or use of physical barriers has two objectives- to insulate buildings from the entry of termites by physically baring their passage with an impenetrable material, and to readily show during an inspection the mud evidence of termites traversing such a barrier if they do reach one. There are three groups of physical barriers, all covered in the Australian Standard:
Metal or other impenetrable capping
The metal termite cap fitted on top of piers or stumps is the most recognisable example. A modification of the single cap is the capping installed along lineal foundation walls and steps. Many older buildings have wooden or stone foundation piers/stumps which enable termites to penetrate up the middle without showing the tell-tale shelter tube. However, once they reach the metal capping, they have to go around it and in so doing the mud is visible to an inspector. It is important that these caps are not nailed or spiked on top of the wooden stump because, as the metal corrodes at the nail hole over the years, sufficient gaps may appear for termites to get through undetected.
These barriers may be of galvanised steel, zincanneal steel, sheet copper, stainless steel or other alloys. They are placed on piers, single brick walls and cavity walls with the protruding metal edge turned down at an angle. Even though this angle may not be specified at 45 degrees or more, termites can still negotiate the obstruction by constructing a thickened shelter tube over it. The protruding edge must ensure that termites have to declare their presence by building mud shelter tubes out over the edge of the shield in order to get further up into the timber content of the structure.
Different termite access opportunities arise in the concrete slab-on-ground modes of construction. Water, gas, electricity and communication entry points into a building are usually located in the foundations. Metal capping /shields are used in varying sizes and dimensions to provide termite barriers at these points.
Experience and surveys in Australia have revealed that the shields are often improperly applied at the time of building and poorly maintained during the service life of a building. Substructures are seldom inspected by homeowners, and relying on the presence of shields without inspection gives a false sense of security.
Stainless steel mesh barriers
In these barriers the mesh is so fine that termites cannot penetrate. When made of a specified grade of stainless steel (lesser grades of stainless steel may corrode) and properly installed, the building is protected from the attack. Australian Standard requirements and installation procedures must be met or exceeded.
Finely divided aggregate barriers
A finely divided form of basalt was first tested in Hawaii against the pest termite Coptotermes formosanus. The particle size was 1.7-2.4mm so that termites could neither move the particles nor pass between them. Granite was tested in Australia and was found to give similar protection for the same reasons. When used both on buildings being erected and on existing buildings, mainly in slab-on-ground construction, the particles become an effective barrier. Specifications are also detailed in the Australian Standards.
Use of chemical barriers
Subterranean termites make their tunnels mostly underground from their nests. Once they are near a food source which is not in the soil they can make shelter tubes over vertical surfaces such as piers and foundation walls to gain access to wooden components of a building, where their presence may be concealed within gyprock walls, panelling etc.
A building can be isolated from termite attack by placing a chemical barrier of insecticide in the soil around the foundations.
These insecticides can be deterrent or non-deterrent to termites wishing to traverse from surrounding untreated soil to the building. In essence, the deterrent insecticides provide a detectable toxic residue which will either discourage the potentially invading termites from attempting to breach the barrier, or will kill enough termites to deter a sustained attack. Non-deterrent chemicals have no repellent value; however, as the termites traverse the soil, the residues are cumulatively absorbed and may spread throughout a nearby colony, resulting in the ultimate demise of the colony. Advocates of the non-deterrent approach suggest that there is a distinct advantage to this method because the carry-back effect kills off colonies surrounding the building, thus reducing pressure on the barriers and warranties offered by the pest manager. However, there can be no certainty that such chemicals will actually be contacted by surrounding colonies, which may continue to mount attacks on unprotected wood/food sources.
The purpose of chemical barriers applied as liquids or sheeting is to provide a continuous and encompassing layer of insecticide between the surrounding soil and the foundations of the building. This layer can be of treated soil of specified thickness and depth, or it may be insecticidal sheeting that may also double as a waterproof membrane.
Chemical barriers can be placed prior to the building foundation work and in accordance with the relative Australian Standard. In the event of termite attack on existing buildings or the eventual degradation of the chemical potency of the insecticide over the years, liquid barriers may be reapplied.
Liquid application of termiticide is usually applied in stages as the building is constructed. Soil is soaked at specified rates that are partly dependent on soil type just before any membrane, reinforcing and concrete is put in place. The aim is to use sufficient liquid to impregnate enough soil so that the barrier is of appropriate width and depth. It is false to assume that by increasing the concentration of chemical in the water that the width and depth of the barrier can be reduced and be as effective. There is provision for a reduction of volume in heavy clay soils because of reduced absorption, but a higher volume of treated soil provides better protection levels.
After the building has been completed, perimeter chemical barriers are applied. This is usually done by trenching and flooding to prevent termite ingress from outside the building. The perimeter treatment should be applied after the construction is completed and the final outside soil levels have been graded prior to laying pavers or concrete paths. Using pavers instead of concrete is sensible because pavers can easily be lifted whereas concrete has to be drilled. Regaining a continuous barrier under concrete is always difficult.
For a barrier treatment to meet the Australian Standard(s) both the underfloor and the perimeter treatment must be completed.
Reticulation systems can be installed using a complex system of pipes and outlets with a treatment point outside the building for repeat application in later years. The systems are installed before the slab is laid. Over time, soil may subside and the sand covering the soil before the concrete is poured may drop away and leave a small gap which the reticulation system can flood at treatment time. Perimeter systems can be installed under concrete paths adjoining the building walls or even around the entire building; however, incautious gardening with big implements could damage unprotected pipes.
A similar reticulation system exists for houses with suspended floor construction, and can be installed beneath existing houses or buildings.
Chemically impregnated sheets/membranes are installed prior to the concrete slab being poured in accordance with the appropriate Australian Standard and Building Code of Australia. Application is only be accredited workers. The easily handled sheets are placed and joined to suit under-slab, utilities entry point and perimeter requirements. The chemical concentration is constant and a visual check can ensure there are no gaps prior to continuation of the building work. Trails are being extrapolated to 50+ years of protection.
Existing buildings
Where termites have attacked existing buildings, eradication procedures should be attempted. The fact that termites achieved entry to the building indicates that the barrier, if any has been bridged. A new application of chemical barrier treatment is sensibly recommended, and unless a barrier treatment is done warranties are not usually given. Such barriers do not necessarily eliminate a colony – the purpose is to isolate the building from reinfestation.
A barrier is established under suspended floors by trenching around foundations, scarifying the soil where necessary or injecting the soil with an insecticide approved for this purpose. Where a barrier is required around a concrete slab, usually a trench is dug around the slab/or holes are drilled through surfaces such as tiles. These treatments are detailed in an Australian Standard.
Where it is suspected that a colony exists under a slab/patio/garage or where an external treatment is not appropriate, the slab may be drilled around the periphery and the insecticide applied. Complete drilling and injection through the top slab surface may be required in certain circumstances. This often involves lifting carpets and relaying them. Floor coverings such as tiles and parquetry flooring are usually damaged during these drill and flood treatments.
A client may be opposed to the use of any of these long term, residual chemicals for financial, environmental or health reasons and will only agree to a dust eradication treatment. In this case a pest manager cannot give any warranty to as dust treatments are often unsuccessful and because other nests may exist. Nests often occur in neighbouring properties, which may deprive the pest controller of access. In such cases a soil barrier treatment and aggregation stations become the only protection options for the house or the building.
Moisture
Subterranean termites depend on moisture for establishing and maintaining their colonies. Moisture is also required by the wood decay fungi from which termites obtain much of their protein. By reducing moisture surrounding and under buildings to make the environment less attractive to termites, the likelihood of infestation will be reduced but not eliminated,
Ventilation of the subfloor area reduces the moisture content of the air and prevents condensation of water on the wood. Wire mesh ventilators allow maximum passage of air.
Leaking drainage pipes and water pipes provide termites with the soil moisture that they require. Such leaks such should not be tolerated. Condensate drainage from air conditioning units should go into the plumbed drainage system rather than drip onto lawns, gardens or paving. Natural seepage may be reduced by the installation of subterranean agricultural drains. Gardens which abut a building wall are usually kept moist for the wellbeing of the plants, but because termites are most likely to be found foraging in moist than in hard, dry soils, they will be encouraged closer to any barrier aberration.
Removing Surrounding Wood
Wooden framework left in place after building has been completed and offcuts of timber left in the soil provide termites with decaying wood in which a new colony can begin.
The use of untreated railway sleepers for garden beds provides termites with decaying wood in moist situations- ideal conditions for termite development. The use of sleepers in landscaping has produced termite problems.
Pressure-pretreated sawn timber and natural rounds, mostly radiata pine, are favoured for landscaping as they are not attacked by termites and generally survive the life of the landscaped area. Transmission and power poles are pretreated and inspected regularly to prevent attack by subterranean and dampwood termites.
The space behind walls is often used as a dumping place for timber offcuts, stumps, branches etc. Always suspect termite activity even if the wall is constructed by masonary.
Removing dead trees and tree stumps
When a tree is removed some of the truck is often left behind even if it had been ground down below soil level. These tree remnants provide a nesting area not only for subterranean termites but also for dampwood termite species. Dead roots left in the soil may also become infested.
Use of resistant timbers
The use of termite resistant woods for building had little, if any, practical relevance today as availability and price usually determine which timbers are used.
Where the termite hazard is great, pressure-pretreated timber or natural rounds may be used with confidence. However, termites often construct their shelter tubes over treated timber to gain access to non-resistant timbers.
Pine timbers have a natural resistance to several species of the genus Nasutitermes. These species prefer hardwoods such as eucalypts; however, other termite species that enjoy pine timber are often also in the vicinity.
Care with building additions and renovations
Adding new rooms, patios, a second level, a pergola, or maybe even a cubby house or kennel may provide a “bridge” across a previously installed barrier, opening up access to termites and causing subsequent extensive damage to otherwise protected buildings. Council building requirements for the installation and application of physical and chemical barriers should be followed to the Australian Standard(s).
Houses often change ownership and the relevance of barriers should be passed on to the new owners at the time of the sale. The gradual degradation of barriers is often not realised by homeowners and if at least annual inspections are not made, termites can cause extensive damage by the time they are discovered years later.
Frequent inspections and constant awareness by the householder are important in minimising damage to the structural and joinery of a building where termites are known to have occurred or where the hazard is great. Phillip Hadlington and Ion Staunton 2008 .