Wind-driven rain reaches places plain rain doesn’t
In still air, rain falls mostly on the top of a chimney, where the crown and cap shed it. In a coastal wind, rain hits the faces of the stack and the flashing on the windward side. Porous brick soaks it up, open mortar joints take in more, and flashing that only just keeps out vertical rain lets driven water past.
That is why leaks near the water often appear only in certain storms. A chimney that stays dry for months can leak in a northeaster because the wind direction finally lines up with its weakest face. Noting the wind direction when a leak appears is one of the most useful clues for finding it.
What salt does to metal parts
Caps, flashing, chase covers and the fasteners holding them are metal, and salt speeds up corrosion. The American Galvanizers Association notes that structures within a mile of the shore can see very different corrosion rates depending on wind and sheltering, and that surfaces directly facing the ocean can show rust years sooner than sheltered ones.
For a chimney that means a galvanized cap or chase cover facing the harbor may rust through far sooner than the same part inland. Stainless steel and copper cost more but last much longer in salt air. For flashing, the same logic applies, along with careful choice of fasteners so dissimilar metals don’t corrode each other.
Mortar and brick near the water
Masonry that stays wet longer and is soaked more often goes through more damaging freeze–thaw cycles. Salts carried in the water can also crystallize in the brick as it dries, adding to the stress. Efflorescence, the white bloom on brick, is the visible sign that water and salts are moving through.
The answer isn’t a hard, impermeable mortar or a film-forming sealer, both of which trap moisture and make damage worse. It is sound joints in a mortar matched to the brick, a crown that sheds water clear of the faces, and, where brick is porous and exposed, a breathable water repellent applied after repairs.
Storms and the top of the stack
The New Bedford Hurricane Barrier, built by the Army Corps of Engineers after the hurricanes of 1938, 1944 and 1954, protects low-lying land in New Bedford, Fairhaven and Acushnet from storm tides. It does nothing about wind. The part of a chimney above the roof takes the full force of storm winds, which is why loose top courses, tilted caps and cracked crowns are common findings after a major storm.
Choosing materials that last on the coast
- Caps: stainless steel or copper rather than galvanized steel, sized and fastened for wind.
- Chase covers: stainless steel, sloped so water runs off, with a drip edge.
- Flashing: durable metal, properly stepped and counter-flashed, not sealed with caulk alone.
- Crowns: properly formed with an overhang and drip edge, so water falls clear of the brick.
- Mortar: matched to the brick, especially on old chimneys built with lime mortar.
Flashing and crowns take the brunt
Two parts of a chimney decide most coastal leaks. The first is the flashing where the chimney meets the roof. On the windward side, driven rain hits the joint at an angle and is pushed up and under anything that relies on gravity alone. Step flashing woven into the shingles, with counter-flashing set into the mortar joints and lapped over it, handles that; a bead of caulk does not, at least not for long.
The second is the crown. A thin mortar wash flush with the brick faces lets wind-driven water run straight down the stack and into every hairline crack. A properly formed crown, sloped and overhanging with a drip edge, throws water clear of the brick. Where a crown has cracked, sealing it early with a product made for crowns, or replacing it if it has failed, saves the masonry below from years of soaking.
Inside the house: what coastal damage looks like
- Stains on the ceiling or wall beside the chimney that appear only in certain storms.
- A rusting damper or water in the firebox after wind-driven rain.
- White salt deposits or peeling paint on the chimney breast indoors.
- A musty smell from the fireplace in humid summer weather.
A coastal maintenance rhythm
- Have the chimney inspected every year, as NFPA 211 recommends, ideally before the heating season.
- Look at the chimney from the ground after every major storm.
- Replace rusting metal parts before they fail, choosing corrosion-resistant metals.
- Deal with cracked crowns and open joints early, before water reaches the core of the stack.
Sources we checked
- American Galvanizers Association: Hot-dip galvanized steel in coastal climates
- BSCES: Historic New England Infrastructure — New Bedford Hurricane Barrier
- NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances
General information for homeowners from Chimney Champ’s New Bedford. It cannot stand in for an inspection of your own chimney, and questions about code are decided by your local building or fire official.