If you have just bought a house with a fireplace, or are thinking of installing a wood stove for heat, it is a good idea to inspect the chimney and flue. If they have been properly maintained and protected from water damage, then most chimneys will prove to be sound and ready for duty, but it pays to be safe where fire hazard is concerned in your home.
Most chimney damage happens in the portion above the roof, so an inspection begins there. Most houses have only one chimney, but it can contain multiple flues if there is more than one fireplace in the home. A modern furnace and a fireplace should not be going through one flue, they should each have a separate flue, and any stove used for wood or coal heat should definitely have a dedicated flue.
If your house doesn’t have a fireplace and the chimney flue does not seem to be connected to your furnace, then it was probably built for wood or coal heating, especially if you have round sheet metal covers on your walls (they may be covered over with wallpaper, plaster or paint). These are flue covers.
Chimney Top Inspection
Anyway, back up on the roof, the first step will be to inspect the chimney top. Your chimney should have a solid mortar cap on it that looks like a cone, sloping away from the flue, to shed water and prevents moisture damage to the top masonry joints.
Some chimneys have a flat slab cap which acts a rain cover. In either case, the cap should be in good condition- if it is cracked or crumbled away, it will need replacement. A cap in bad condition will allow rainwater and moisture into the brick or stone masonry, and they will soak it up, expanding and cracking the mortar joints.
The mortar between bricks or stones should be sound. Probing into the mortar joints with a screwdriver up and down the chimney should not reveal excessive crumbling. One or two loose joints and a cracked brick or two will mean a repair job, with re-pointing and replacement of bricks.
Many rotten joints and missing bricks can mean you will need to have the chimney rebuilt from the top down to at least a foot below roof level; this can be costly, needless to say. Make sure your inspector is qualified and experienced if this is his diagnosis.
The next thing to check is the flashing where the chimney structure mates with the roof. Older houses will have lead sheets, but most flashing is made of strips of copper sheeting. One edge of the strip should be either mortared directly to the masonry of the chimney, or embedded in mortar joints, or on some roofs, covered entirely in tar.
The flashing should run down to the sheathing of the roof and several inches out under the shingles or whatever roof covering you have. Any missing flashing or flashing in bad condition should be repaired or replaced.
The inspection of your chimney’s mortar joints and masonry is now repeated, all the way down to the foundation. You will need access to the attic, all floors and basement. Loose mortar, cracks and dark sooty streaks are what are looked for. Any problem spots are to be noted and assessed for repairs.
The condition of the flue and chimney is now checked for leaks, unless the chimney has been found to be in need of replacement. The inspector will check for leaks by plugging up the opening at the chimney top with some kind of fireproof tightly fitting block, then lighting a smoky fire in the fireplace or wood stove with an oily rag.
Any leaks in the flue will be visible as wisps of smoke escape from the chimney, and the inspector will mark their place for repair. Sometimes there will be so many wisps the chimney will need to be rebuilt or replaced completely.
Photo by Mark Kobayashi-Hillary, Creative Commons Attribution License