Timber Treatments and Pest Control

Chemical treatments to control rot to timber, insect damage, or insect swarms may harm bats. Treatment may not be necessary. It is important to get expert historic buildings and bat protection advice, whether you are the building owner, manager or contractor. Only products suitable for use near bat roosts should be employed.

Treating timber and 'bat appropriate' chemicals

If timber requires treatment, you should first carry out a bat survey. A specialist timber consultant should be commissioned to diagnose and treat timber in traditional buildings and he/she will need a copy of the bat survey report.

The first question to consider is whether the timber needs treating at all.

  • Is the problem current or historic? If historic, then treatment is not generally necessary; the existence of insects' flight holes in structural timber or furniture does not necessarily mean the infestation is still live.
  • What is the extent of the damage? Usually only the soft outer part of the timber (sapwood) is attacked by wood-boring insects, unless the heartwood has been modified by fungal attack or has little natural durability. In many roof structures, the strength lies in the heartwood so minor outer damage may not require treatment.
  • Do you need to solve an underlying problem? The dry rot and wet rot fungi that destroy wood need a narrow range of conditions of moisture, temperature and humidity. Whichever type of rot you have, first stop the water ingress which has caused the damp conditions which the fungus needs to survive. Allow the environment to dry out and the moisture levels in the affected timber to reduce before assessing whether further work is needed. Replacing the timber or applying a chemical without solving the source of damp would treat the symptom but not the cause, and the problem would be likely to recur.
  • If you have to treat any unfixed furniture or movable fittings, move and treat them outside so that no fumes reach the bats.

Some remedial timber treatments, including ‘bombs’ and fogging systems, are harmful to bats if they are exposed directly to them. This is a particular problem on roof timbers as bats often roost on the wood itself. Vapours from treatments used on lower floors and joists, however, may also affect bats roosting at roof level. Treatments which use petroleum products to spread the pesticide and aid its penetration are especially likely to release vapours that could harm or disturb bats.

Bats can also be harmed from contact with timber treatment residues as they regularly groom themselves.

Natural England publishes a list of timber-treatment chemicals suitable for use in or near bat roosts, after taking specialist advice.

Light traps and sticky traps are sometimes useful for confirming insect activity but not for eradication. They must only be used after taking specialist advice.

Managing rot

If timber in a building is found to be rotting, it's essential to identify the source of the moisture and remedy its cause to prevent a recurrence. This will avoid inappropriate, costly and damaging treatment from being undertaken and needless disruption caused to bats and to the building.

Regular maintenance can prevent most causes of moisture ingress. Some buildings, owing to their original design, construction and siting - or the importance of their collection - may require a building management system to control the relative humidity or moisture levels. If repairs or modifications to the roof and walls of the building to prevent water ingress are needed, follow the advice given by your bat specialist.

Controlling flies, other insects and pests

Insect pests may use the same roof voids and entrances as bats.

Fly-papers, impregnated strips and ultraviolet electric zappers should not be used if there are bats. Wiping down surfaces to remove any pheromones left as attractant signposts by the insects can help reduce the number of flies. When wiping down painted woodwork or stonework or metalwork, use as little water and detergent as possible (a couple of drops). This will avoid damage to the paintwork and underlying materials. If wiping down paintwork, test a small area first to ensure the stability of the paint.

However, care needs to be taken when eradicating insects, pests or vermin to make sure the treatment does not harm the bats and you do not disturb the bats. Get advice from a specialist.

Natural England provides guidance about using pest control products in or near bat roosts. You can also get advice from the National Bat Helpline 0345 1300 228.

Open bait vermin traps can be harmful to bats if they find themselves on the floor of roof spaces.