Why chimneys leak, and how St. Louis homes get them fixed

A water stain on the ceiling next to the chimney does not always mean the chimney itself is broken. Water can get in at several points, and the fix depends on which one.

Where the water gets in

• No cap. Rain falls straight down the flue. A cap is often the cheapest fix.
• Cracked crown. The concrete top of the chimney cracks and lets water into the brick.
• Flashing. The metal where the chimney meets the roof can lift, rust or lose its seal.
• Brick and mortar. Old, soft brick and worn joints soak up water like a sponge.
• Condensation. A furnace or water heater venting into an old flue can make moisture inside it.

Old brick in the city

Much of St. Louis is built from soft red brick and lime mortar. Hard modern mortar can crack old brick faces over time. Ask whether the crew matches the mortar to the brick.

Narrowing it down

Note when it leaks. During every rain points to the cap, crown or flashing. Only in wind-driven rain points to the brick face. Only in cold weather with the furnace on points to condensation.

Fixes, smallest first

• Add or replace the cap
• Seal or rebuild the crown
• Reflash where the chimney meets the roof
• Tuckpoint worn joints
• A breathable water repellent on sound brick
• Rebuild the top courses if brick is crumbling

Act before winter

Water in brick freezes and pushes the faces off. A small leak in fall can mean loose brick by spring.

Ask for photos

Ask the inspector for photos from the roof so you can see the problem yourself before you approve work.