How to Cap a Chimney

If you no longer have an active chimney then it’s a good idea to cap off the top, this may improve the thermal efficiency of the home and you won’t have to worry about birds getting into the stack.

This type of work is best done by a professional unless you have a good head for heights!

There are several options for you to consider. It all depends on whether you intend to restart the chimney at a later date and if the chimney is vented. Remember – if you don’t allow for adequate ventilation you will most likely suffer from condensation in the chimney shaft and possible damp patches on the wall.

Here are the most common methods used by builders and other tradesman:

  • A simple cap – usually a patio slab that is cemented to the top of the chimney
  • Take the chimney down – easy to do with small chimneys
  • A breather cowl – allows for some ventilation of the flue/stack

A Simple Cap

Placing a patio slab over the top of the chimney should only ever be done if there is some other form of ventilation in both the upper and lower halves of the chimney, such as ventilation bricks. It is quite rare for a chimney to have a vent in the upper half of the stack so it would be better to install a breather cap or cowl.

Take The Chimney Down

This option is best for standalone small chimneys, it can be very easy to dismantle a small chimney to just below a the roof and then install a few metres of felt, timber baton and some roof tiles.

Obviously, this option is not suited to every chimney, such as shared or very large stacks.

Use a Breather Cowl

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There are dozens of different chimney cowls on the market, many are designed for disused chimneys and act a breather/ventilator (like this one from online retailer Amazon).

Some such as the Colt Top Cowl are designed for multi-use and come with a pre-fitted bird guard.

Once you have a cowl or vent of some kind at the top of the chimney, it is still a good idea to install a vent in the lower half of the chimney to create an upward airflow that will prevent condensation but without causing loss of heat issues.

If there is a concern about condensation or damp then a Colt Top cowl should be ised instead of a breather cap.