How To Build a Fireplace Chimney

When building a fireplace in your home you will have to consider not only the visible hearth but also the fireplace chimney, which is the working component that guides smoke and sparks safely out of your home. There is some important information you need to know if you plan to tackle this task yourself in order to avoid chimney fires and poor construction problems.

Building the Chimney

The measurements of a chimney are a minimum of four inches bigger in all directions than the flue. Wood, kindling, and other materials that may travel up the chimney must be at a minimum of two inches away from the outer part of the chimney. Outside chimneys can be only one inch from the outer wall of the home.

Code requires that chimneys be three feet over the roof and two feet over any other part of the roof that is within 10 feet. You can use a precast concrete cap that has a drip edge and then use a silicone sealant on the joint that is between the cap and the top of the flue.


If you are concerned about earthquakes or anything that might unsettle the chimney, you can put a #4 reinforcing bar in the corners of the chimney. The best place for the reinforcing bars are in the cells of the bricks. Grout these bars into place. If you can’t put the reinforcing bars in the cells of the bricks, place them between the flue liner and the rest of bricks surrounding it.

Wrapping the Flue

Wrap the flue liners with 1/8-inch ceramic fiber paper socks, sealing the area. This will give the flue liner room to expand or shrink without breaking the liner or the masonry around it.

Finally, bind the materials around the flue liner every 18 inches with pencil rods in the joints. If you have an exterior chimney, it needs to be anchored both at the floor and roof.