Mastering Roof Inspections: Roof Penetrations, Part 2

by Kenton Shepard and Nick Gromicko




Chimney Inspection:  Part 2

Inspecting the chimney exterior is the same as inspecting the exterior walls of the home. You'll be looking for and commenting on the defects common to whatever type of material is installed.


If the chimney is wider than 30 inches in the direction parallel to the ridge, it should have a cricket installed on the uphill side.



A cricket is a small roof designed to keep runoff from pooling on the uphill side of the chimney. Framing the cricket will create a couple of little valleys which need to be flashed correctly.

If a chimney that should have a cricket is missing the cricket, mention that in your report and explain why they’re a good idea.

This cricket valley flashing has visible corrosion and accumulated debris. When you see this condition -- and it’s common -- scrape away the debris and check the condition of the flashing. Debris will hold moisture against the flashing, and corrosion is likely to advance more quickly in these areas.


You’ll see chimney caps made of sheet metal, usually galvanized, but sometimes copper, both of which have long lifespans.

Concrete is also used and it’s durable.

Probably the most common material is mortar, which is not so durable, but tends to spall and crack, especially in cold climates.

Spalling is surface deterioration.

Occasionally, the cap is missing.

Especially on brick chimneys -- which are everywhere -- a mason was probably up there on the roof finishing off the chimney, and he had a big tub full of mortar.  He may have dumped the mortar and cleaned the tub, and then mixed a batch of concrete just for the chimney cap.  But most masons just use the mortar instead of doing the extra work, so you’ll see a lot of caps with cracks.

Recommend that cracks in mortar be sealed. In cold climates, moisture will freeze in the cracks, expand them, and pretty soon chunks of mortar will be falling off the roof. If you see any cracks at all, recommend annual inspection and maintenance of the chimney cap.


The chimney flue is the lining of the chimney interior -- usually made of tile or metal -- which prevents the hot, toxic and corrosive combustion gasses from damaging the chimney structure or entering the living space.

Looking down into the chimney.  You should see an intact flue.

You’ll be looking for and reporting, as defects:  cracks; flues that are unlined; or flues that are not lined all the way to the top.


Chimneys which have no lining look like this.
Brick and mortar will be deteriorated over the long-term by exhaust gasses.

The fireplace served by this chimney had been converted from a wood-burner to a gas insert. Apparently, the flue termination needed to be raised to meet the manufacturer’s requirements. The inexpensive fix was to stack more flue tiles to raise the point of termination. This is not the preferred method, but it does give you a good look at the flue tiles. It’s not high-quality work, but it’s not necessarily a defective installation, either.

You should also call a defect any debris you see in the chimney. Debris may collect from overhanging tree branches or from animal activity.

Spark Arresters

Spark arresters are not required by the IRC, but local AHJs may require them.

Spark arresters serve two purposes:

They keep burning embers from becoming airborne and landing on combustible materials where they may start a fire, and…

…they keep wildlife, such as raccoons, out of chimneys.

You’ll see a variety of designs. This one is designed to swivel to improve chimney draft, and some…

…are just plain unique. This is the candlestick version.

If a spark arrester is installed, it should meet certain requirements:

  • The net free area of the spark arrester should be at least four times the net free area of the flue outlet. The “net free” opening is the size of the opening after the dimensions of any obstructions are subtracted.
  • Openings should not block the passage of a 3/8-inch sphere or permit the passage of a 1/2-inch sphere.
  • The spark arrester should be accessible for cleaning, and be removable so that the flue can be cleaned.

Attic Chimney

While you’re looking at the chimney where it passes through the attic, look closely to make sure that there are no openings to the flue, and that there are no other conditions that might become a problem.

Here, you’d want to pull aside insulation to see what part of the home structure is supporting the posts that support this chimney; and then you’d recommend correction by a qualified contractor. “Correction,” in this case, would mean removal of the abandoned chimney before it collapses through the ceiling and causes serious or fatal injury.



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