Why Door and Window Frames Are High-Risk
Door and window frames are more vulnerable to termite attack than most people realise, for three structural reasons. First, they are almost always in contact with masonry — set into concrete or brick openings — which provides the concealed pathway that subterranean termites prefer to travel through. Second, the end grain of the timber is embedded in the masonry, giving termites direct access to the most vulnerable part of the cross-section. Third, frames are often painted or varnished on the visible face but left bare on the back face and ends before installation — the surfaces hidden by plaster and concrete receive no protection at all.
The combination of masonry contact, embedded end grain, and uncoated hidden surfaces makes door and window frames a preferred entry point for termites attacking a building. In many cases where termite damage is found in walls, floors, or ceilings, investigation reveals that the frames were the original point of entry.
What Happens When Frames Are Not Treated
Termite damage in door and window frames follows a predictable sequence. Termites enter through the hidden back face or through the embedded end, hollow out the frame interior while leaving the painted exterior surface intact, and then spread into the wall cavity, floor joists, and ceiling structure from the frame as a base.
The damage is invisible until the frame begins to feel soft or hollow when knocked, paint bubbles and peels off hollow sections, or — in the worst cases — the frame collapses under normal door operation or wind load. By the time any of these signs appear, the infestation has usually spread well beyond the frame itself, and the remediation involves removing plastering and finishes to access the full extent of the damage.
The Correct Treatment Specification for Frames
All door and window frames, including sub-frames, architraves, and any timber sill members, should be VPI-treated with Boron Borax before installation. Treatment should be done on the dimensioned frame sections before they are cut to final length and assembled — not after cutting, because cutting exposes untreated end grain.
If frames must be cut on site after VPI treatment, the exposed end grain should be flood-coated with a concentrated borate solution immediately after cutting. This does not replicate the retention level of factory VPI treatment, but it significantly reduces the vulnerability of the exposed surface.
Frames should also be isolated from direct masonry contact wherever possible. A waterproof membrane or damp-proof layer between the back of the frame and the masonry opening prevents moisture wicking from the wall into the timber — moisture that creates the conditions termites require and that degrades even treated timber over long periods.
- Specify VPI treatment for all frames, sub-frames, sill members, and architraves
- Treat before final cutting and assembly to protect end grain
- Flood-coat any site cuts with concentrated borate solution immediately after cutting
- Isolate frame back face from masonry with damp-proof membrane
- Specify treatment records from an IPPC-registered facility for compliance documentation
Specifying Treated Frames to Builders and Contractors
The challenge with door and window frame treatment is that it is easy to omit at the specification stage and very difficult to retrofit once the building is plastered. Architects and quantity surveyors should include VPI treatment for all timber joinery in their standard schedules of works, with a requirement for treatment records to be submitted before plastering or other concealing finishes are applied.
Builders who resist treated timber specification on cost grounds should be shown the cost comparison: treated frames add a modest amount to the frame cost; untreated frames, when they fail, require stripping plaster over a wide area, replacing structural elements that may have been compromised, re-plastering, repainting, and treating the termite colony — a project that costs many times the original treatment cost.
St. Xavier Timber supplies VPI-treated timber cut to door and window frame dimensions. We issue treatment records with every order and can supply in the quantities needed for individual houses or large developments. Contact us with your dimensions and required quantities.