Termites and decks: protection, gaps and who inspects
Where subterranean termites are a known risk, the building code’s Housing Provisions treat a deck as an attachment to the building, and give two options: a termite management system to the attachment, or an inspection zone between the attachment and the building. After handover, NSW Fair Trading’s Guide to Standards and Tolerances says “it is the owner’s responsibility to regularly inspect the property, including sub-floor inspections, to detect evidence of termite attack.”
This guide describes the building rules in general terms; it isn’t pest-control or building advice. The official text is the ABCB’s Housing Provisions, Part 3.4, and Building Commission NSW explains NSW’s approach.
When do the termite rules apply?
(1) “The requirements of this Part apply where:” (a) “a Class 1 or 10 building is constructed in an area where subterranean termites are known to present a potential risk of attack; and” (b) “a primary building element of a Class 1 or 10 building is considered susceptible to termite attack.”
(2) “For the purposes of (1), a primary building element consisting entirely of, or a combination of, any of the following materials is considered not subject to termite attack:” (a) “Steel, aluminium or other metals.” (b) “Concrete.” (c) “Masonry.” (d) “Fibre-reinforced cement.” (e) “Timber”, “naturally termite resistant in accordance with Appendix C of AS 3660.1.” (f) “Timber”, “preservative treated in accordance with Appendix D of AS 3660.1.”
Quoted from the ABCB Housing Provisions 2022, Part 3.4. The words inside quotation marks are the code’s own; the commas after “Timber” stand in for its dashes. The NSW schedule lists no NSW variation to Part 3.4.
The code’s own explanatory note adds that masonry is not subject to termite attack, “however termites may gain entry through mortar and other joints”. In NSW, the Guide to Standards and Tolerances says a termite management system is needed only where the primary building elements are susceptible to termite attack under the Building Code of Australia’s definition.
How does the code treat a deck?
Table 3.4.2 lists acceptable termite management systems by building element. For “Attachments to buildings” it gives two options: a termite management system to the attachment, or an inspection zone between the attachment and the building. The explanatory note lists decks among those attachments, alongside items such as downpipes, steps, verandahs, porches and carports.
Where a system is required, it must comply with AS 3660.1 or have passed the tests in Section 5 of AS 3660.3, have a durable notice, and, where it is chemical, use a chemical on the appropriate authority’s pesticides register.
- 1A gap between the deck and the building. WoodSolutions says that where a barrier is the method chosen, AS 3660.1 requires a deck or similar attachment to stand at least 25 mm clear of the building; if not, the barrier must be extended to take in the deck.
- 2Posts on galvanised metal stirrups with at least 75 mm clearance above finished ground level, which WoodSolutions gives as one way to achieve termite protection.
- 3Boards parallel to the house screwed rather than nailed, so they can be lifted for inspection without damage.
What are the three ways WoodSolutions describes?
WoodSolutions’ deck guide reads the code’s requirements for decks as three alternatives.
| Method | What it means |
|---|---|
| Naturally termite-resistant timber | Constructed from naturally termite-resistant timbers, in accordance with Appendix C of AS 3660.1. |
| Preservative-treated timber | Constructed from preservative-treated timber in accordance with Appendix D of AS 3660.1. |
| A termite barrier | A barrier protecting the primary building elements, installed in accordance with AS 3660.1. |
The guide counts the framing members, the decking boards, stairways and ramps as primary building elements, being the elements that take part of the building load. For decks less than 400 mm off the ground it asks for termite-resistant timber only, and a gap of at least 40 mm between the house and the deck for pest inspection and air flow.
Alternatives to timber posts include metal posts or brick piers, with a termite cap between the pier and the bearer; where engaged brick piers support bearers, the guide says AS 3660.1 requires a 25 mm gap between the timber and the building envelope.
Where is the record of what was installed?
“A durable notice must be permanently fixed to the building in a prominent location, such as in a meter box or the like, indicating”: (a) “the termite management system used; and” (b) “the date of installation of the system; and” (c) “where a chemical is used, its life expectancy as listed on the appropriate authority’s register label; and” (d) “the installer’s or manufacturer’s recommendations for the scope and frequency of future inspections for termite activity.”
Quoted from the ABCB Housing Provisions 2022. The words inside quotation marks are the code’s own; the colon outside them stands in for its dash.
NSW Government also suggests keeping a copy of the warranty and instruction sheet for any anti-termite protection work among your building records.
Whose job is it?
While it is being built
Building Commission NSW says that when you build or renovate, the builder is responsible for installing a termite risk management system for the work. It warns that some building contracts may try to shift that liability to the owner, and suggests reading your contract carefully to understand who is accountable for termite protection.
After handover
The Guide to Standards and Tolerances is direct: checking the property for termites, under the floor included, is the owner’s job, and it should be done regularly. It explains that termites can get around properly installed protection, for example by building tunnels around barriers; regular inspections can find the tunnels, and when they are found, a suitably qualified pest controller should find the termite nest and destroy it.
On damage, the guide says termite damage outside areas the council has designated as termite risk areas is the owner’s responsibility. Inside designated areas, damage is a defect if the system wasn’t installed in accordance with the Building Code of Australia, and is not a defect if the owner didn’t maintain the system, made it non-compliant after handover, or didn’t maintain it in accordance with the manufacturer’s instructions and AS 3660.2.
The code puts it in one line: “In addition to correct installation of a termite management system, its effectiveness will rely on regular maintenance and competent inspection.” It also notes that Australia has more than 350 termite species, and that about 30 of them do costly damage to buildings.