Timber Pest Advice – A technical guide
Here is all you need to know to perform a fairly detailed inspection of your own property.
1. General recommendations
1.1 Regular inspection of all structural timbers
The Forestry Commission advises inspections at no more than 12 monthly intervals unless the type of construction is timber pest resistant. Australian Standard 4349.3 “Inspection of Buildings – Timber Pest Inspections” recommends annual timber pest inspections as a minimum. The Building Code of Australia and other Council regulations allows the use of untreated timbers for your building. These timbers can be extensively damaged by undetected timber pest damage. The Institute of Building Consultants rates type of construction on the basis of risk of timber pest attack and has designated the following categories:
|Category||Pest Inspection Required||Frequency of inspection|
|Resistant||No||Check joinery timbers annually|
|Low Risk||Yes||12-24 monthly|
|Moderate Risk||Yes||12 monthly|
|High Risk||Yes||6 monthly|
|Extreme Risk||Yes||3 monthly|
Frequency of 6 and 3 monthly inspections of properties should be reviewed after a period of no further infestation. More frequent inspection may also be warranted (in interconnected terraces/buildings for example, where disturbances in one property may divert termite activity to another).
1.2 Inspection access
Inspection access to all sub-floor and structural timbers is preferable. In some types of construction, access may be poor and difficult to achieve (in flat roofs for example). However, in cases where access can be improved, such changes should be considered a high priority. In relation to sub-floor access, this means, where possible:
- cutting a floor for access to all sub-floor timbers
- in some cases, cutting a floor trap in one room may provide access to the sub-floor of that room only and more traps may need to be cut for other rooms
- in cases where the floor frame is close to the ground (and no crawl space exists), more than one trap may be required per room to view timbers adequately.
Any changes that are made to improve access should be permanent and easily recoverable for future regular inspections. Clearance to sub-floor timbers should be 400mm minimum and 700mm preferred in all cases.
1.3 Concealed timber structures
Concealed wall frame timbers particularly in timber-framed and brick veneer houses cannot be inspected. No reliable assessment of their soundness and condition can be given, except by removal of skirtings and wall linings or through use of a fibrescope. The cost of repairing potentially extensive timber pest attack is high where damage goes undetected or where these types of structures cannot be regularly inspected. This is especially a problem with untreated, timber-framed buildings on concrete slabs on ground.
In some cases, the installation of removable skirtings (minimum 75mm width and screw-fixed to facilitate regular removal) is suggested to allow inspection of bottom plates and base of wall studs.
Note also: Spaces in timber wall frames provide harbourages for various timber pests, particularly where vermin barriers are damaged or missing.
1.4 Termite damage that appears inactive
Determining whether or not termites are active, (or potentially active), when signs of what appears to be old inactive termite mudding and/or damage are found, is sometimes inconclusive and may require follow-up monitoring. Termites operate like a huge army of individuals that often work (collect food) at a variety of locations at any given time, however, they consistently maintain contact with the main nest.
Termites may temporarily vacate a particular ‘work’ site because of a variety of disturbances such as:
- occupants of house concerned at discovery of termites spray workings with an inappropriate aerosol insecticide
- recent previous inspector probed and disturbed the then active termite workings
- recent attempt at control of infestation by pest control operator has temporarily diverted activity to another (possibly concealed) location
- recent or current building activities may have temporarily diverted activity away from accessible timbers.
1.5 Ventilation and drainage
Most timber pests (including termites, some borers and wood decay fungi) become more active when conditions are moist. Such conditions also favour the growth of many moulds, some of which will produce airborne spores that will provoke allergic responses in some people.
High levels of moisture in sub-floor areas are often caused by poor ventilation and drainage. Buildings built on sandy soils (which don’t retain moisture as readily) can often cope better with less ventilation than ones located on loam or clay soils.
In general, sub-floor areas should be well ventilated and drained – no flooding or ponding water should occur (refer to further comments on ventilation in section 2.16). Note also: untreated softwood should not be used for sub-floors with less than 1350mm clearance to the ground.
1.6 Physical barriers
Ant caps (termite shields and capping) located between masonry piers/dwarf walls/stumps and structural timbers do not prevent termites from gaining access to building timbers, but they do make termite entry more visible during inspections.
Damp courses prevent moisture movement in masonry structures but faulty ones can lead to rising damp. Insertion of ant caps and damp courses after completion of construction is usually difficult and expensive, while the installation of brick piers is less so.
1.7 Chemical Barriers – Soil treatments against termites
Many houses, particularly those with a history of termite damage, will have had chemical barrier treatments carried out to prevent termite entry. Traditionally, such treatments involved the use of persistent Organochlorine chemicals. With increased concerns about the health and environmental effects of these materials, their use has now been banned and a less persistent Organophosphorus insecticide has replaced them.
Chemical barrier treatments are best considered a last (albeit sometimes necessary) resort. More sound approaches to termite control include:
- attempting to locate and then destroy the nest
- in cases where the nest cannot be located arsenic dusting methods can be used to try and destroy the termite colony.
- judicious use of chemical barrier treatments in cases where the above approaches are unsuccessful.
Prevention of termites is best accomplished by:
- adopting building practices that minimise the likelihood of termite entry/activity (e.g. use of termite resistant materials such as durable (natural or treated) timbers.
- eliminating the conditions which favour termite attack in existing buildings.
(Refer to further comments in section 2.20 below.)
1.8 Planning renovations, additions or new building work
The addition of a concrete slab floored extension at the rear of a house with a suspended timber floor can adversely affect the ventilation of the sub-floor area and cause wood decay problems. Such an extension can also be finished in a manner which leaves it prone to concealed termite entry over the slab edge and into wall frame timbers.
Your building consultant can advise you on how to use timber pest resistant construction methods and non-chemical modifications instead of relying on chemical soil treatments under new extensions or buildings.
People entering sub-floor areas to inspect or carry out work on buildings with known or serious timber pest problems should consider such environments as being potentially contaminated with toxic materials and wear appropriate protective clothing and equipment (including overalls, gloves and a suitable respirator).
This warning extends to termite-damaged timbers in the building which may have been treated with arsenic dust.
2. How to handle timber pest problems
Pests that damage timber will nevertheless remain an important part of our ecology and they should be considered both as a potentially troublesome and expected aspect of home ownership. The following notes should provide some guidance in dealing with the more common timber pest problems:
2.1 Fungal Decay (wood decay or wet rot)
Fungal decay is a type of timber damage caused by a live fungus which requires high moisture levels before it can inflict damage on the timber. Timbers suffering from decay may be stained, soft, spongy or broken up into cubes and are often reduced in strength. Most decay problems are resolved by reducing the exposure of the timber to high moisture levels.
What to do:
2.1.1 Exterior timbers
Minor wood decay is common in many exterior timbers that are exposed to the weather or prolonged moisture. Protective coatings to exterior timbers should be well maintained. Sealing of cracks and joints with a flexible sealant is advisable prior to the application of protective coatings. Sawn ends of timber (including joins, corners and mitres) are particularly prone to moisture absorption and deteriorate with the onset of decay.
This may occur in timbers associated with window frames/mullions, pergolas, balconies, fascias and barges. In cases of advanced decay, repairs/replacements may be necessary (preferably with durable timbers). Reducing exposure to excessive moisture is the preferred approach if feasible.
Fences in particular show weathering and wood decay damage, which may range from minor to severe. Untreated fence posts set into the ground commonly succumb to decay at the base and this can lead to collapse. If palings are in reasonable condition, re-supporting the old posts with galvanised iron tubing or angle (e.g. 50mm x 50mm) set in concrete footing can lengthen the life of the fence considerably. In cases where built-up garden soil or mulch is in direct contact with base of palings (or railings), these timbers are prone to (further) wood decay damage and concealed termite activity. It is best to avoid such contact by lowering soil/mulch levels or shortening fence palings. In cases where the fence is acting as a retaining wall, construction of a properly designed retaining wall with a generous gap between it and the fence is advised. Treated pine fencing is resistant to wood decay and insect attack.
2.1.3 Leaks from shower trays and wet area floors
Leaking shower recesses (or associated plumbing leaks) can lead to considerable wood decay damage to adjacent timbers such as structural wall and flooring timbers if allowed to leak for a prolonged period. The extent of damage to accessible wall and flooring/floor frame timbers and skirtings can usually be determined. However, the full extent of damage (including damage to concealed wall frame timbers) cannot be assessed without the removal of wall linings. In the case of leaking shower trays, failures are most often caused by cracking/leaking at the wall/floor junction. The application of sealants is generally considered unreliable for the longer term.
The preferred approach is installation of a waterproof shower tray and this usually involves removal of the floor tiles and lower wall tiles (or all wall tiles if penetrating damp is likely to be a problem as well). This is followed by installation of the waterproof tray and then re-tiling. Matching the original tiles may be difficult or impossible. Specialist waterproofing companies are usually engaged for this type of work and a builder or carpenter may be needed if structural repairs to damaged timbers are required (for cost implications see Section 4.46).
2.1.4 Timber penetrating ground
Untreated timbers built into or onto the ground (soil, concrete or pavers) are very prone to wood decay. The sawn end is particularly prone to moisture absorption and subsequent rot. Such timber is also prone to concealed termite entry. Timbers commonly damaged in this way include:
- door jambs/architraves (which may be shortened to avoid ground contact)
- pergola/deck/carport support posts/timber stumps
- staircase/steps stringers which are best altered by inserting a metal bracket (stirrup) between the base of the timber and the ground (engage building consultant to ensure correct detailing).
If changes are not made, the timber remains prone to further decay damage and concealed termite entry so regular monitoring is recommended. In some cases, insertion of slow release wood preservative sticks, as an attempt to lessen the susceptibility to timber pest activity/damage, may ‘buy time’.
2.1.5 Sub-floor timbers in contact with moist masonry
In some older styles of buildings (such as Victorian or Federation style homes), structural flooring timbers (bearers, joists, floor plates) may rest directly on moist sandstone or brick masonry. In such cases, localised wood decay damage may occur at and around the point of contact. For example, the floor plate, which rests on masonry and supports the ends of floor joists may show varying levels of decay damage. The ends of bearers or joists resting on moist masonry may deteriorate considerably. Repairs needed can vary from relatively minor lengthening or supporting/wedging of the damaged end section of a joist, to jacking entire sections of floor to replace floor plates and repair, strengthen or replace bearers or joists. Low sub-floor clearances can make this kind of work more difficult and/or expensive.
While the process of decay in such cases is often a slow one (this can vary with the durability of the timber species, moisture levels and other factors), it is likely that insertion of a damp course material between timber and masonry will be beneficial. Sub-floor areas subject to problems of this kind will often benefit from ventilation or drainage improvements (see Section 2.16 below).
2.1.6 Sub-floor ventilation
Sub-floor spaces, if not sufficiently well ventilated, can raise the moisture content of timbers to such an extent that decay damage results to structural and/or flooring timbers (such problems are less likely in houses located on sandy soils). In older buildings, severe damage may result in excessive floor movement which will require repairs. In some newer buildings, signs of surface mould growth on soil, timber or masonry surfaces may indicate that conditions are conducive to decay problems in the longer term.
Methods of improving ventilation range from relatively minor work such as clearing weeds or stored goods from existing vents to replacing existing terracotta vents with larger cement/mesh types. More serious and expensive undertakings may include installing vents in sandstone walls or in interior walls for cross-ventilation.
In situations where normal ventilators cannot be installed (where floor levels are below outside grade level, for example) installing fan assisted ducted systems may achieve the desired improvement in air circulation. Also, systems may operate with an electric fan set on a timer or they may be connected to a roof mounted turbo vent which will pull air whenever a breeze turns the fan. Solar powered fans are now available.
All wall vents should be kept free of obstructions especially soil, plants and debris. Area of vents – dimensions of vents should not be less than the equivalent size of 450mm x 150mm per linear metre. Corrosion resistant wire mesh and cement type vents which are vermin proof are the preferred option. Internal foundation walls should have ample openings for ventilation without affecting structural stability.
Termites (also called White Ants) are social insects that behave like a well organised army and attack most untreated softwood and hardwood timbers.
Timbers damaged by termites are usually hollowed out and the insects often build mud tunnels and pack feeding areas with mud in order to maintain relatively high moisture levels for themselves. They usually have a nest from which they operate. Destruction of the nest, if it can be located, is the preferred method of control. Where attempts at nest destruction are unsuccessful, a chemical barrier treatment may be applied to help prevent termite access into the building.
What to do:
Try and identify the termite species but with minimal disturbance. This usually requires finding a specimen of a soldier termite.
Termite workings (such as damage sites, mud leads or hollowed timbers) should not be disturbed as this may cause the termites to vacate workings and interfere with control attempts. If the species can cause severe damage and is in, or close to, the building:
Investigate previous termite history (such as infestation or treatment) with owner or neighbours or from visual evidence noted during our inspection (e.g. drill holes in concrete slabs).
Engage licensed Pest Control Operator to undertake control procedures, preferably in an environmentally sensitive manner that may incorporate the following strategies:
- attempt to locate nest and destroy the nest if found;
- if nest cannot be found, attempt destruction of remote colony with careful application of poisonous dust that should be carried back to the nest;
- judicious use of chemical barrier treatment if considered necessary.
If the Pre-Purchase Property and/or Timber Pest Inspection Report identifies termite damage, engage your Building and Timber Pest Consultant to determine the full extent of damage and need for repairs (including investigation of concealed structural timbers where appropriate) and undertake repair works. When structural damage occurs, repairs can be extremely difficult and costly. The extent of damage can only be determined by opening up the building fabric. If such repairs require people to work in a confined area, such as a sub-floor, that is to be chemically treated (i.e. barrier treatment), it is recommended that repairs are completed prior to any chemical treatment. In cases where chemical treatment precedes repair works, wearing appropriate protective clothing and equipment (including respirator) and time delay between treatment and building works is advised (consult your pest controller/consultant about the timing treatment and repairs).
Reduce preconditions for future termite attack:
- obtain access to all inaccessible areas
- remove timber debris from sub-floor area.
- remove unnecessary form-work timbers, especially those in contact with ground in sub-floor area.
- remove (or monitor) dead trees or tree stumps near house.
- store firewood up off ground, under cover and preferably away from building
- avoid long term storage of building timbers in contact with ground.
- untreated hardwoods used in landscaping (eg sleeper retaining walls, hardwood garden edging) are prone to decay and termite harbourage
- replace with treated pine or masonry or regularly monitor for signs of increased timber pest activity.
- avoid tree roots entering sub-floor area as these can provide access for termites.
- timbers penetrating ground (e.g. pergola posts, door jambs, steps stringers) can provide points for concealed termite entry to attached structures. Alter to avoid direct contact with ground eg installation of metal stirrups.
- where base of exterior wall cladding (e.g. weatherboards) are in contact with ground (paving, soil etc) decay damage is likely and concealed termite entry is possible. Alter to avoid such contact.
- keep exterior perimeter of concrete slab edges clear of weeds, built-up garden beds, raised paving levels etc so as to avoid concealed termite entry over slab edge and into wall (and possibly roof) frame timbers
- avoid excessive moisture in and around sub-floor areas, e.g. maintain good ventilation and avoid entry of storm water, rectify any leaks in water and drainage pipes. Check regularly for leaks under sinks, taps and refrigerators.
2.3.1 Furniture beetle (Anobium punctatum )
This insect is a small beetle that, during its grub (larval) stage, resides within and chews timber for periods of up to a few years. At the completion of feeding, the grubs pupate near the surface of the timber and soon after change into an adult beetle that makes a small round hole when it emerges. Many types of old pine (softwood) timbers are susceptible and this borer commonly attacks old pine flooring (not Cypress Pine), built-in closets, fireplace surrounds, staircase timbers and furniture.
What to do:
- Normal inspection procedures cannot determine whether or not the borers are still active. The most practical method for determining activity status is to monitor damage levels. Try to establish whether any new holes are appearing over time (in the case of floor boards for example, square off a few sections of the underneath of the boards with carpenter’s pencil or texta and circle all of the emergence or exit holes). If the beetle infestation is still active, it is likely that new holes will appear each spring (usually October-November). Re-examine each year for signs of new activity.
- Infestations of furniture beetle in old pine flooring may, over a period of many years, result in such severe damage that floor replacement is required. In other cases, damage remains at minor to moderate levels and activity may have ceased. In such cases, only occasional boards may require strengthening/replacement. (A Building Consultant can give advice on the extent of structural damage and need for repairs).
- Where the borers appear to be active in valuable furniture (such as antiques), consider having the article(s) fumigated by a company that carries out such work: the process of fumigation usually uses non-residual poisonous gases that provide no protection against future infestation.
- Where only a few shelf timbers show furniture beetle damage, it is advisable to properly dispose of damaged timber and replace with resistant timber species (hence lessening the chances of an infestation developing in furniture, if activity was present in the shelf timbers)
- Minor damage levels to floorboards do not affect structural strength but may become visible if floors are sanded/polished.
- Replace severely damaged timbers with a suitable Anobium resistant timber such as Cypress Pine or any hardwood species such as Brush Box or Tallowwood.
- Replacement of infested timber is the preferred method of reducing further infestation. Chemical spray treatments are sometimes considered unreliable (largely because the grubs reside well within the timber and surface sprays may not be fully effective). Note: In cases where replacement is not feasible, consultation with a Pest Control Consultant may find a chemical strategy that is appropriate (by careful timing of treatments and/or modified application techniques for example).
- Sub-floor areas with higher moisture levels are favourable to the development of these borers. Consider improving sub-floor ventilation.
- Always check incoming furniture (particularly older furniture/antiques) for signs of Anobium borer damage (symptoms are small round holes containing gritty frass – ‘borer dust’) as this may facilitate a new infestation.
2.3.2 Powderpost beetle (Lyctus brunneus )
This small beetle attacks only the sapwood section of certain species of hardwood timber. It prefers recently seasoned timbers and is unlikely to be active in timbers that are more than about 15 years old. Evidence of Lyctus damage is often encountered in hardwood floor frame and roof frame timbers. However, it usually involves only a corner or edge of the timber (showing small round holes and a fine frass or ‘borer dust’) and very rarely presents a structural problem.
Although possibly active in newer buildings, it is unlikely to cause any serious damage as it only attacks the sapwood section of timber (and the amount of sapwood in building timbers is regulated by the Timber Marketing Act in NSW). If more than 25 percent of the perimeter of structural timbers appears to be affected, (or signs of Lyctus damage become evident on manufactured or moulded items such as doors or architraves), then an infringement of the Act may have occurred. Complaints may be lodged within 24 months of purchase of the timber material. For enquiries contact the Forestry Commission of NSW. Stiffen or replace any severely affected timbers.
2.3.3 Timber defects caused by forest insect pests
There are a variety of insect pests of forest trees that cause various kinds of damage or defects which can be found in timbers used in buildings.
A range of insects including moth caterpillars, various beetle grubs and termites can damage the wood in standing trees and if, after milling, the damage is considered too minor for rejection of the timber, then the timber is sold and incorporated into buildings.
Damage caused by forest timber pests is inactive and presents no threat to the building structure. Such damage may appear as small to large, oval or round holes or tunnels – sometimes filled with grass if caused by moths or beetles or it may appear as hollow grooves if caused by termites.
3. Defibration of timber
Defibration of timber (sometimes referred to as delignification) is a process in which timbers (most commonly roof timbers) undergo a slow breakdown whereby the ‘glue’ that normally holds wood fibres together breaks down to give the timber a furry or woolly appearance. Exposure to high levels of atmospheric sea salt is though to be the main cause and higher temperatures and moisture probably assist the process.
While the process appears to be a slow one, it has been suggested that lowering roof temperatures, minimising the accumulation of atmospheric sea salts and reducing roof moisture levels may all assist in minimising further damage. These conditions may be achieved by installation of roof sarking, increasing roof ventilation and by not exhausting bathroom and kitchen fumes into the roof void.