How Long a Chimney Chase Cover Lasts

How a Chase Top Is Built

The chase is the framed box on the roof that hides a factory-built fireplace's metal chimney. Its top is closed by a sheet-metal cover with a collar for the pipe, and above that sit the storm collar and the listed termination cap. The Superior wood fireplace instructions describe the original: a 28 gauge galvanized steel flashing with a hole and a 2 inch collar, set on noncombustible spacers and nailed through the sides, with ventilation openings left unsealed.

Every part of that assembly has to keep water out of a wooden box. The cover's life is really the life of that job.

• Termination cap on top of the metal chimney.
• Storm collar around the pipe, caulked where it meets the outer pipe.
• Cover collar rising around the pipe.
• Cover pan across the chase top, with a skirt down the sides.
• Chase siding and framing below.

What Wears a Cover Out

The American Galvanizers Association names five things that set how fast a zinc coating wears outdoors: temperature, humidity, rainfall, sulfur dioxide pollution and air salinity. It explains that the zinc forms a protective film in wet and dry cycles, which holds unless it meets aggressive chlorides or sulfides. Every one of those factors acts on a galvanized chase cover, and more of them act at once where the weather is warm and wet or the air carries salt.

The Majestic MPL11 fireplace manual points to the weakest spots: its chimney metal has a rust-protective coating, but the cut edges are not protected. On a chase cover, the edges of the skirt, the collar hole and every screw hole are cut edges.

Shape decides the rest. A flat pan sags a little in the middle over time, and water sits there after every rain. Standing water keeps the zinc wet instead of letting it cycle dry, and the puddle is where rust starts. A cover with a slope or a cross break sheds water to the edges. Our page on chase cover metals compares galvanized, stainless, aluminum and copper.

The Stages, From the Ground

You can follow a cover's life from the yard with binoculars. Do not climb onto the roof to look; a chase top is a fall risk even for people who do it every day.

Watch the timing of the stains: rust streaks that appear after rain and grow each season mean the metal is losing, not just the paint.

• Dull gray: the zinc has weathered, which is normal.
• Light brown spots around screws and edges: the cut edges are rusting.
• A brown ring or puddle mark in the middle: water is ponding and the coating is gone there.
• Orange streaks running down the chase siding below the skirt: rust is washing off the pan.
• Pinholes, a soft or sagging center, or a lifted collar: the cover is finished.

Signs It Is Leaking Already

A cover can fail before it looks bad from the ground. The Majestic manual lists leakage of rain water into the home among the results of a poor installation, and a rusted pan or a dried-out seal at the storm collar does the same thing. Inside, look for water stains on the ceiling or wall near the fireplace, rust on the fireplace's top or damper, a musty smell when it rains, or swollen trim around the chase. Any of these means the chase top needs a look before the framing below suffers.

Slowing It Down

A galvanized cover in good shape can be kept going. The Majestic manual tells owners to wash exposed metal with detergent and paint it with a galvanized primer to prevent rusting and staining. The DuraTech chimney instructions allow high-temperature, rust-proof paint on exterior parts after a vinegar and water wash, but never on the chimney cap itself.

Two other habits help: keep the storm collar sealed, which both manuals cover, and keep the termination's own openings clear. Both are roof jobs, so leave them to a crew with fall protection.

When It Has to Go

Paint and sealant only help metal that is still sound. Once a cover has holes, a sagging center or a loose collar, it is replaced, and the replacement should fix the reason the old one failed: a slope or cross break instead of a flat top, a metal that does not depend on a zinc coat, fasteners that match it, and a collar sized to the listed termination.

A replacement is also the moment to check the chase framing under the old pan, because a cover that leaked for a while may have left soft or stained wood behind.

Our Chase Top Visit

On a free inspection we check the cover, the collar, the storm collar, the termination and the chase walls, and tell you plainly whether the cover has life left. If it does not, our chimney chase cover service measures and fits a new one, and any rot is written up with it in one estimate.

Chase tops are roof work, and our experienced crew does it with fall protection. Ours is a local, family-owned company in Spring Hill and Proudly American, and the Proudly American crew on your roof is our own, cleaning up before it leaves.