Woodworm Treatment Calculator — How Much Treatment Fluid Do I Need?

For curative treatment of an active infestation, manufacturer datasheets (Safeguard SoluGuard, Barrettine Woodworm Killer) specify 300 ml per m² — about 3.3 m² per litre per coat. Preventative protection of sound timber needs less: 200 ml per m² (around 5 m² per litre). For moderate to heavy infestations, 2 coats are typically required, with 48–72 hours between coats. The total timber surface area is greater than the floor area because joists have multiple exposed faces — for floor joists, multiply your floor area by roughly 1.1 (two sides plus the underside; the top sits under the floorboards) to get the treatable surface area.

Active woodworm produces fresh frass (fine, powdery sawdust) below exit holes, and the holes will have clean, sharp edges with pale-coloured wood visible inside. Old, inactive holes appear dark and dusty. The flight season for common furniture beetle is May to September, so check for fresh holes and frass during these months. You can place paper beneath suspected timber to check for fresh frass over several weeks.

Structural repair is needed when woodworm damage has significantly reduced the cross-section of load-bearing timbers such as floor joists or roof rafters. If you can push a screwdriver or penknife easily into the timber, or if the timber sounds hollow when tapped, it may have lost structural integrity. Heavy infestations with dense exit holes covering more than 50% of the timber surface typically indicate the need for structural assessment by a timber specialist.

The most common is the Common Furniture Beetle (Anobium punctatum), which produces 1-2mm exit holes in softwood. Death Watch Beetle (Xestobium rufovillosum) attacks hardwood, particularly oak, in older buildings with 3mm holes. House Longhorn Beetle (Hylotrupes bajulus) is mainly found in Surrey and the south-east, attacking softwood roof timbers. Wood-boring Weevil (Euophryum confine) attacks already-decayed timber and indicates a damp problem.

PCA (Property Care Association) guidelines recommend treating all accessible timbers in the affected area, not just those showing visible signs of infestation. Larvae may be present inside timber that shows no external signs yet. For roof spaces and sub-floor voids, all accessible timber surfaces should be treated. This preventative approach ensures complete protection and is the standard practice for insurance-backed guarantees.