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Chase Cover Materials: Galvanized vs Stainless vs Copper
A chase cover is the metal lid over a framed chimney enclosure. The metal it is made from, and the way it is shaped, decide how long it keeps water out.
Why the material matters
A chase cover (sometimes called a top pan) sits on top of the wood-framed enclosure around a factory-built chimney. It is flat metal exposed to rain, snow and sun, so it is one of the first parts to show rust. If you are not sure what a chase cover is or how it differs from a cap or crown, start with crown vs cap vs chase cover and masonry vs factory-built chimney.
The three common metals
| Metal | How it protects itself | What to expect |
|---|---|---|
| Galvanized steel | A zinc coating over steel | The zinc wears away over time. Once enough is gone, the steel underneath shows red rust. Wet, humid or salty conditions use up the coating faster. |
| Stainless steel | Resists rust on its own | Generally lasts longer than galvanized, but it is not immune. Salt air is described as particularly hard on it. |
| Copper | Forms a surface patina as it weathers | Changes color over the years, from brown to blue-green or gray-green. Weathering copper can stain the materials below it. |
Zinc coatings are rated by weight, and in a given environment a heavier coating lasts proportionally longer. That is one reason two galvanized covers can age very differently. Metal suppliers also note that galvanized covers rust faster than stainless ones.
What actually causes a chase cover to corrode
- Standing water. A cover that is flat, or that has dipped, lets water sit and speeds up rust and leaks. A cover shaped so water runs off lasts better.
- A coating that has worn through. On galvanized metal, rust appears once the zinc is gone in an area.
- Weather and air. Frequent dampness, pollutants and sea salt all speed up corrosion of zinc and some stainless grades.
- Rust staining. Rust streaks on siding below a chimney usually trace back to the chase cover, not the cap.
Sizing and shape: general points
Chase covers are made to fit the framing, not bought off a shelf in one size. Suppliers ask for measurements on all four sides, with an allowance added so the cover overhangs the enclosure, and extra clearance around each flue or pipe opening. A skirt that folds down over the sides and a small drip edge at its lower edge help keep water off siding or brick. Diagonal creases in the top help water drain instead of collecting. A tight fit and a drained surface matter as much as the metal itself. Specific slope and gauge are decisions for the installer who measures your chimney.
Signs your chase cover needs attention
- Rust spots, flaking, or orange streaks running down the siding
- Pooled water on the top after rain
- Stained or damp-looking siding or wood around the enclosure
- Water stains on the ceiling near the chimney
A rusted or flat cover can leak. For other possible leak sources, see why is my chimney leaking and choosing a chimney cap. Our Monroe Township project and Berkeley Heights project both involved chase cover work.
What a pro checks
During an inspection, we look at the cover’s condition, fit, slope and seams, and at the framing and flashing around it. If the cover has to be replaced, the new one is measured to your chimney. See chimney caps and chase covers. Ask for the material and the shape of the cover to be written into the quote.
Frequently asked questions
Is a rusty chase cover an emergency?
Usually not by itself, but a cover that holds water can end up leaking. Have it looked at before that happens.
Can a rusty cover be painted or sealed?
Coatings and sealants can be part of a repair, but they will not fix a cover that is flat, holed or badly corroded. Have it assessed first.
Which metal should I choose?
It depends on your location, budget and how the existing cover failed. Ask your contractor to explain the options for your chimney.
Do all chimneys have a chase cover?
No. Brick and stone chimneys have a crown instead. Chase covers are used on framed, factory-built enclosures.
Next step
If your cover is rusting or holding water, request a visit or call (862) 225-6529. We will look at the cover and the framing around it.
Sources
- American Galvanizers Association, GalvInfo Note 1.6 (zinc coating is consumed over time, red rust follows; environment and coating weight affect life)
- Copper Development Association, architectural FAQs (copper weathering and patina, staining of nearby materials)
- Black Goose, chimney cap vs chase cover (supplier page: galvanized vs stainless, flat covers collect water, salt air; rust streaks usually from the chase cover)
- Rockford Chimney Supply, stainless chase covers (supplier page: measuring, overhang and opening allowances, skirt, drip edge, creases)