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

This calculator estimates the quantity of woodworm treatment product needed based on the floor area affected, the type of timber, severity of infestation and your chosen treatment method.

The formula

Spray: Litres = (Floor Area × Surface Multiplier ÷ Coverage Rate) × Number of Coats

Coverage rate = 3.3 m²/L for curative treatment (300 ml/m²) or 5 m²/L for preventative (200 ml/m²).

Paste/gel: Kg = Treatable Surface Area × 0.57 kg/m²

Surface area multipliers

Treatable timber surface is larger than the floor area. The multipliers below are derived from typical timber sizes at standard centres (e.g. 47×200mm joists at 400mm centres ≈ 2.5 linear metres of joist per m², with two 200mm sides plus the 47mm underside ≈ 1.1 m² of timber per m² of floor):

• Floor joists: ×1.1 (two sides and underside; top sits under the floorboards)
• Floorboards: ×1.2 (top and underside)
• Roof rafters / purlins: ×1.4 (exposed faces in the roof void)

Coverage rates

• Insecticidal spray (curative): 300 ml/m² ≈ 3.3 m² per litre per coat — typically 2 coats for moderate to heavy infestation (preventative is 200 ml/m² ≈ 5 m²/L, 1 coat)
• Insecticidal paste/gel: ~0.57 kg per m² of timber surface for a brush-applied boron gel coat (e.g. ProBor 20, 1 L per 2–2.5 m²)
• Micro-injection: boron paste cartridges (310–400 ml) — holes at ~150mm centres along the timber. Per-point volume is a rule of thumb; aim for the datasheet loading of ~5.9 L per m³ of timber

Severity guidance

Light infestations (scattered holes) typically need 1 coat. Moderate and heavy infestations require 2 coats. Heavy infestations where timber is softened may require structural repair — replacing affected joists, rafters or floorboards after treatment.

Standards

Treatment should follow PCA (Property Care Association) Code of Practice for Remedial Timber Treatment. Products used should be HSE-approved for use against wood-boring insects. For insurance-backed guarantees, work should be carried out by a PCA-registered contractor.