New Build: Prevention Is the Only Strategy
In new construction, timber treatment is purely preventive — the timber goes into a building that has no established pest population or decay, and the goal is to ensure it stays that way. The tools available in new construction are comprehensive: you can specify the species, control the moisture content, apply factory VPI treatment before installation, design in DPC isolation at masonry contacts, and require documentation before concealing finishes are applied.
All of these tools are available at low cost and with minimal disruption in new construction — and none of them are available once the building is built. The decision not to specify treated timber in new construction is a decision to accept the future cost of remediation as a certainty rather than an avoidable expense.
Renovation: Assessment Before Specification
Renovation projects have a fundamentally different starting condition: some or all of the existing timber may already be infested, decayed, or stressed. Before specifying replacement timber or additional treatment, the condition of the existing structure must be assessed. Opening up sufficient ceiling and wall areas to inspect the structural timber is not a cost; it is the minimum information required to design the remediation correctly.
The assessment should establish: which members are sound (no decay, no active infestation, adequate structural section), which are compromised (some decay or infestation but structurally adequate with propping), which must be replaced immediately, and whether any active termite colony is present. An active colony that is not treated before the structural work will simply reinfest the new timber installed to replace what it damaged.
Dealing with Active Termite Colonies in Renovation
If an active termite colony is found during renovation — evidenced by live termites in mud tubes, in damaged timber, or in the soil — the colony must be treated before new structural timber is installed. Installing VPI-treated replacement timber into a building with an active colony reduces re-infestation risk significantly, but it does not eliminate the colony. The colony will survive in the soil below the building and will continue to seek new food sources.
Colony treatment options include soil barrier treatment (applying a liquid termiticide to the soil around and under the building to create a chemical barrier), baiting systems (slow-acting baits that worker termites carry back to the colony, eventually killing the queen), and physical barriers (stainless steel mesh or aggregate barriers at the foundation level that prevent termite access). The appropriate approach depends on the type of construction, the accessibility of the soil, and the severity of the infestation.
In-Situ Treatment for Retained Structural Members
For structural members that are assessed as sound but have been exposed to risk — either from adjacent decay, from known termite activity, or from persistently high moisture — in-situ borate treatment provides a measure of protection without the disruption of full replacement.
In-situ treatment involves drilling a grid of holes into the timber member and injecting a concentrated borate solution under pressure or by gravity. The solution diffuses through the moisture in the wood and distributes the preservative through the cross-section. The level of penetration and retention achieved by in-situ treatment does not match factory VPI treatment — it is a remedial measure for sound timber at risk, not a substitute for VPI in new construction.
Replacement Timber in Renovation
Replacement structural members installed during renovation should be specified to exactly the same standard as new construction: kiln-dried to the target MC, VPI treated with Boron Borax, with treatment records. The fact that a building already exists and has existing timber does not reduce the standard required for the replacement material — if anything, the high-risk environment revealed by the need for renovation increases the case for the highest available treatment standard.
Replacement timber is often installed in more difficult conditions than new construction: working in confined roof spaces, connecting to existing members that may not be at the ideal MC, and installing before the moisture problem that caused the original failure has been fully resolved. These conditions increase the importance of starting with the best possible treatment on the replacement timber.
St. Xavier Timber supplies VPI-treated replacement structural timber for renovation projects and can turn most orders around within 3–5 working days. We issue treatment records with every order. Contact us to discuss your renovation specification and timeline.