A chimney bird guard is a sturdy cap fitted into or onto the outlet of a flue to stop birds nesting in it. In practice it is almost always a combined product: the same cap keeps rain out of the flue as well, so it doubles as a rain cap.
Why fit one
- Nests. Jackdaws in particular like to build in an open flue. A nest blocks the flue completely. With an open fire or a stove that means smoke blowing back into the room; with a gas appliance it means a genuinely dangerous carbon monoxide situation.
- Rain. Water falling down the flue attacks the joints, causes damp patches on the chimney breast, and in a masonry flue can lead to frost damage.
- Pests. A cap with mesh also keeps wasps and other animals out.
How it is made
- Material — usually aluminium or stainless steel, and sometimes ceramic on a modern chimney with a ceramic liner.
- Size — caps come in a range of diameters; on a round flue the internal diameter governs, and on a square masonry flue a cap with a square base or an adaptor plate is used.
- Fixing — with spring legs or set screws inside the flue, or with a base plate on the chimney pot.
Points to watch
- Do not confuse it with a spinning cowl. A bird guard keeps birds and rain out; a rotating cowl is meant to cure downdraught. That is a different problem with a different solution.
- Watch the free area. A cap with mesh that is too fine, or too little height under the hood, throttles the flue. Use a cap approved for the type of appliance.
- Not every appliance should have one. With some room-sealed gas appliances using a concentric flue, the terminal is part of the appliance and no separate cap belongs on it.
- Plan access. Combine fitting with sweeping or roof maintenance — hiring a scaffold or a platform twice is expensive.
Related terms
- Chimney
- Flue
- Chimney cowl
- Roof penetration
- Collar
- Lead flashing
Want to know more about construction terms? Visit our knowledge base at fredsdiyplans.com.