Chimney repair above the roofline in Washington, DC

This page is about the brick and mortar you see sticking up through your roof. The crown, the cap, the joints and the top courses take direct rain, wind and freeze-thaw on all four sides, and they wear out long before the chimney inside the house does.

The metal where the roof meets the brick is a separate job. If your problem is a leak at the base of the chimney, the step and counterflashing are the first suspect, and our page on chimney flashing repair covers that work. On many houses we do both at once, because new flashing needs sound mortar joints to hold it.

We don't work inside the flue or the firebox. If anything we see from the top, like crumbling clay tile liners or heavy soot, suggests the flue needs a look, we'll ask you to have a chimney sweep inspect it before the chimney is used again, and we'll time our masonry work around their visit.

The crown is the concrete or mortar slab that covers the top of the chimney around the flue. On most older houses around Washington it's just a sloped mound of mortar troweled over the last course of brick. That mortar shrinks, cracks and lets water straight down into the core of the chimney.

A proper crown is cast or formed at least two inches thick, overhangs the brick by an inch or more with a drip groove underneath, and is separated from the flue tile by a bond break so the two can move independently. When a crown has only hairline cracks we seal it with a breathable crown coating; when it's broken into pieces we chip it off and form a new one.

The cap is the metal hood over the flue opening. Without one, rain falls straight down the flue, and squirrels, raccoons and nesting birds move in. We install stainless steel or copper caps with a screen, sized to cover each flue or the whole crown on a multi-flue chimney.

Washington winters swing above and below freezing dozens of times. Water soaks into soft brick and mortar, freezes and expands, and over the years the joints wash out and the brick faces pop off in flakes. That flaking is called spalling, and once the hard outer face is gone the brick soaks up water even faster.

Much of the spalling we see on older chimneys was caused by an earlier repair. Brick laid before about 1930 was set in soft lime mortar, and someone later repointed it with hard Portland cement mortar. The hard mortar doesn't give, so the stress goes into the brick instead. We grind out the joints to about three quarters of an inch and repoint with a lime-rich mortar that's softer than the brick.

Individual spalled or cracked bricks get cut out and replaced with salvaged or reclaimed brick close to the original in size and color. We don't paint or seal over damaged brick, because trapping moisture behind a film usually makes spalling worse.

When the top two to six feet of a chimney have loose bricks, open joints all the way through or a visible lean, repointing won't hold it together. The fix is to take the chimney down course by course to solid masonry and rebuild it on that sound base.

We set up roof brackets and planks around the chimney, lower the old brick to the ground in buckets, and clean and reuse the good brick where we can. The rebuild goes back to the same height and corbel pattern, with new flue tile extensions if needed and a new formed crown and cap on top.

On slate roofs we stage the work so nobody stands on the slate, and we replace any pieces cracked by falling mortar. Our slate roof repair crew handles that part on the same visit. If the flashing is old, it makes sense to replace it while the chimney is rebuilt, because the new counterflashing can be built into the new joints.

Most rowhouses in DC were built with coal-burning fireplaces, and their chimneys rise from the party walls. Many haven't carried smoke in decades. They still catch rain, and an unused chimney with a broken crown is one of the most common sources of damp walls we trace on a Capitol Hill or Columbia Heights rowhouse.

You have three choices. We can repair and cap the chimney with a vented metal cover, which keeps rain out and lets the stack breathe. We can rebuild the top if it's unstable. Or we can take it down below the roofline, fill or cap the flues, and roof over the opening so the membrane runs straight across.

Taking a chimney down needs some planning. If it sits on a shared party wall, your neighbor's flues may run through it, so we talk with them first. In a historic district, removing a chimney visible from the street goes through the Historic Preservation Office, and the job generally needs a DC Department of Buildings permit. Our rowhouse roofing crew patches the membrane once the stack is gone. Call (202) 771-7443 to set up a look.