How Do You Stop Birds Nesting in a Chimney?

Why birds choose chimneys

A chimney pot looks like a hollow tree to a bird. It is high up, sheltered from the wind, dry inside and, when the fire is out, quiet. Jackdaws are the main offenders around Basingstoke, and they are surprisingly determined. A pair will carry sticks to the pot all spring and drop them down the flue until a wedge of twigs forms a platform, often a metre or more deep. Starlings, pigeons and sparrows use chimneys too, and so do wasps and bees.

The nest itself is a nuisance, but the trouble it causes is worse. A flue packed with sticks cannot carry smoke or fumes out. A fire lit beneath a nest can set it alight, and a boiler or gas fire flue that is blocked can push fumes back into the house. A nest that gets wet turns to a soggy mass that keeps damp inside the stack and stains the chimney breast. And a bird that falls down the flue may get stuck in the fireplace, which is distressing for everyone involved.

Guards, cowls and caps

The fix is a physical barrier at the top of the pot. There are several kinds, and the right one depends on whether the flue is in use.

• Wire-basket bird guard: a domed or conical cage of stainless or galvanised wire that fits over the pot. Birds cannot get in, and smoke passes freely, so it suits a working open fire.
• Mesh cowl: a pot-top cover with fine mesh around the sides and a solid top. It keeps out birds and rain and suits flues in regular use.
• Rain cap with a bird-proof screen: a hooded cap with openings protected by mesh, suited to a flue that is rarely used but needs to breathe.
• Ventilated cap for a disused flue: a cap designed to keep out birds and weather while leaving air movement through the flue. See our page on capped chimney ventilation.

The mesh size matters. Too wide, and smaller birds get in. Too fine, and soot clogs it quickly on a working fire, so the guard has to be chosen for the fuel burned. If you burn wood or solid fuel, check with your sweep that the guard will not restrict the draught. Our guide to chimney pots and cowls describes the types in more detail.

Timing and wildlife rules

Nesting birds are protected, so you should not remove or interfere with an active nest. If birds are in the chimney in spring or summer, wait until the young have left, then clear the flue and fit the guard. The best time to do the work is late summer to winter, when nests are empty. If you are unsure whether a nest is in use, listen for chirping and look for adult birds going in and out. A roofer or sweep who finds an active nest should stop and tell you. Bats are protected too, and a chimney that is roosting bats needs specialist advice before work. If in doubt, check with Natural England or an ecologist.

The same caution applies to bees and wasps. Do not block a flue with a nest of bees or wasps in it, and do not light a fire beneath one. Pest controllers can deal with an active colony.

Clearing a blocked flue first

If birds have already nested, the flue must be cleared before a guard goes on, or the debris will still be in there. A chimney sweep can remove the nest with brushes and rods, and often with a vacuum to catch the debris. A camera shows how far the blockage extends. Never poke at a nest from the fireplace with a broom handle and then light a fire. Dead birds and fallen sticks can stay lodged at the smoke shelf or at a bend, and trying a fire is how house fires start. Our page on chimney sweep or roofer explains which of the two to call, and in what order.

The roofer's task is the outside. Fitting a guard means getting to the top of the stack safely, usually with a tower or scaffold, and bedding the guard or cowl firmly in fresh mortar. While there, we check the pot, the flaunching and the brickwork, because birds often tear at crumbling mortar and make it worse. If the mortar is loose, repointing at the same visit saves a second trip, as chimney repointing explains.

What it costs

A guard or cowl is an inexpensive item, and the cost of fitting is mostly access. Where scaffold is already up for other chimney work, adding guards costs little. On its own, a visit with a tower or platform will cost more than the guard. Next to the cost of a full stack repair, a simple guard fit is a small item, though it varies with the stack. Your fixed quote follows the survey, and the photographs show every pot as it stands. Return to chimney repairs in Basingstoke for the full list of services.