The top of the chimney takes the most weather of any part of your house. Two components do most of the work of protecting it: the cap and the crown. They are often confused, but they do different jobs.
The chimney cap
A cap is the covered metal hood that sits over the flue opening. It:
- Keeps rain out of the flue, protecting the liner, damper and firebox from water damage
- Keeps animals out. Birds, squirrels and raccoons all like an open flue.
- Blocks leaves and debris that can obstruct the flue
- Usually includes mesh that helps keep sparks and embers from landing on the roof
Caps come in single-flue and multi-flue styles. Stainless steel and copper caps hold up far longer than galvanized steel, which tends to rust. A cap should be sized and secured correctly so it does not restrict draft or blow off in high winds.
The chimney crown
The crown is the concrete or mortar slab that covers the top of the masonry around the flue. Its job is to shed water away from the chimney. A well-built crown:
- Slopes away from the flue
- Overhangs the brick with a drip edge so water falls clear of the chimney walls
- Is separated from the flue tile by a flexible bond break or sealant, so the flue can expand and contract with heat without cracking the crown
Many crowns are built as a thin layer of mortar troweled over the top (a "mortar wash"). These tend to crack quickly as they expand and contract with the seasons.
What failure looks like
- Cracks, gaps or crumbling concrete on the crown
- A cap that is rusted, dented, loose or missing
- Water stains near the fireplace, rust on the damper, or a damp smell after rain
- Spalling bricks or white efflorescence on the upper chimney
- Animals or nesting material in the flue
Repair or rebuild?
Small cracks in an otherwise sound crown can often be sealed with a flexible crown coating made for the purpose. Widespread cracking, crumbling or a poorly designed crown usually calls for a rebuild with proper slope, overhang and a bond break. A missing or failed cap is a simple, inexpensive fix that prevents much bigger problems.
Oklahoma's freeze-thaw cycles turn small cracks into big ones. Checking the cap and crown during your annual inspection is one of the cheapest ways to prevent expensive masonry repairs.