How Not to Install a Metal Chimney Chase Cap

Who wants to climb onto a roof to check the top of the chimney? That’s not a fun task, but it is important. You might find issues that aren’t visible from the ground. Even newly installed caps/flues may have problems.

Boxed-in Metal Chimney Flue

Photo 1 shows the top of a wood-framed chimney chase from the ground. The chase is covered with new vinyl siding and new metal cap/surround. Certainly, the cap has good clearance to the siding, so there is a drip space. But what about the top of the chimney? And what is that thin, raised galvanized section? You can’t check these details from the ground.

Photo 1: Boxed-in metal chimney flue

A View from the Roof

Photo 2, taken from the rooftop, reveals the top of this chase. The chimney lacks a proper cap to direct water over the edge. Some type of caulk joint was applied to the tan metal wrap around the side of the chimney.

Photo 2: Top of boxed-in chase

We can also see the metal flue and cap. Is it missing the storm collar provided with all metal chimney flue pipes? Yes. Is the cap pitched toward the sides of the chimney? No.

Photo 3 provides a closeup of the spot where the chimney cap meets the top of the wood chase. What a mess! Whoever installed the new siding and trim wasn’t thinking about how water flows. You can see exposed OSB on the right side of the chimney and a messy attempt at sealing the joints with caulk.

Photo 3: Closeup 1, top of chase

Photo 4 shows more details of this mess. The tan-colored metal on the outside edge is pitched into the caulk joint, trapping water. This joint allows water to leak into the wood-framed chimney chase and the metal fireplace.

Photo 4: Closeup 2, top of chase

Correct Chimney Chase Details

Illustration F031 shows a cross-section of properly installed metal flues in a wood-framed chase. The flues have storm collars that divert water away from the round flue holes in the metal cap, and they are sealed to the cap. The cap extends over the siding with a drip edge. Ideally, the metal cap/top is creased from corner to corner, slightly raising the center so water drains to the edges.

Illustration F031: Metal chimney in wood frame

Common Problems with a Chimney Chase

Illustration F032C shows problems commonly found on a boxed-in chimney chase. Storm collars are missing. The metal cap is not sealed to the metal flues, and there is no overhang with drip around the chimney. This will result in rust on the cap as well as leaks into the framing and behind the siding. All these defects should be reported.

Illustration F032C: Metal chimney in wood frame, with problems

The Takeaway

Always get a good view of a chimney top during an inspection. If the top is not visible, state that in your report, explain why you can’t see it, and suggest further evaluation.

These pictures show a chimney with new siding and cap. I have found many new boxed-in chimneys with serious defects that allow leaks into the chimney and fireplace.

I always look inside a metal fireplace for any signs of leaks and properly document the conditions—good or bad—including a photo. Any leaks need further evaluation.

To learn more, attend Tom’s technical presentations at educational sessions for ASHI chapters and local groups. Tom can also provide his knowledge for your educational event; contact him at Tom@htoyh.com.