Remedial treatment for biodeterioration

In cases of actual or suspected problems of wood rot or wood-boring insects in buildings, any remedial works should meet the following standards.

1

Investigation should be carried out by an independent specialist consultant, architect or surveyor to establish the cause and extent of damp and timber decay, including the potential risk to the health of occupants, before specification or remedial work. This investigation should include:

• inspection of all accessible timbers to determine whether they are subject to, or at risk from, fungal decay or insect attack; and
• determination as to whether any wood-rotting fungi or wood-decaying insects found are active and whether their activity is significant in each particular case.

2

Specification of remedial work should be prepared by an independent consultant as in 1 above. Such specification should provide for:

• maximum conservation of materials;
• future health of the building and its occupants;
• minimal use of new materials;
• avoidance of chemical pesticide use where possible;
• use of materials and techniques with minimum adverse environmental impact; and
• minimum cost of the whole project including the costs of the proposed works, the disturbance of occupancy, future maintenance costs, and the cost of safe disposal of all waste materials.

3

Remedial building works should be carried out as specified in 2 to control the timber decay, prevent further decay, and correct any significant building defects resulting in conditions of high moisture content or poor ventilation of timber. These should provide for:

• the reduction of the subsurface moisture content of all timber to below 16-18%;
• the isolation of timber from contact with damp masonry by air space or damp-proof membrane;
• the provision of free air movement around timber in walls, roofs and suspended floors;
• humidities in voids not exceeding an average relative humidity of 65%;
• the removal of active fungal material and any timber affected to the extent that its function is compromised or adjacent structures put at risk (in the case of insect infestation, measures to avoid contamination);
• the prevention of, or protection of timber from, sources of water likely to cause wetting such as overflowing gutters, leaking plumbing, condensation and rising or penetrating damp; and
• the removal of all builders' rubbish from voids and cavities, and vacuum cleaning to remove dust.

4

Avoid the use of chemical pesticides wherever possible. Where their use is essential, ensure that:

• the minimum use of fungicides is consistent with the probability of re-infestation in the light of 3;
• insecticidal treatment is limited to the locations of significant active insect attack in the light of 3;
• specific agents to be used on specific organisms only - 'combined', 'general' or 'precautionary' treatments are not to be used;
• fungicides and insecticides are currently fully approved under the Control of Pesticides Regulations 1986 (pesticides with special dispensation or licence as of right are not to be used);
• pesticides are applied in accordance with the manufacturer's instructions and within any regulations, codes of practice, guidelines or recommendations currently recommended by the British Wood Preserving and Damp-proofing Association (BWPDA), the Health and Safety Executive (HSE), or other competent authority;
• the contractor applying the pesticide certifies that the treatment will not damage the health of the occupants and of the structure or wildlife in and around it; and
• the contractor certifies that the disposal of surplus pesticide, pesticide containers and treated waste materials is safe, non-polluting, and in accordance with all current regulations and guidelines.