Chimney flashing repair cost

Rebuilding chimney flashing costs $400 to $1,800, typically around $800. A simple reseal is $200 to $500. A full chimney rebuild above the roofline runs $1,500 to $5,000.

A chimney is a hole cut through the roof with a masonry tower standing in it, and water gets in at the join. It is the most common source of a roof leak, and the leak almost never shows up next to the chimney — it runs down a rafter and appears somewhere else entirely.

What each repair costs

The four parts, and which one is failing

Water can enter a chimney in four places, and the fix is different for each.

Step flashing. L-shaped pieces of metal woven into the shingle courses along the sides of the chimney, one per course. If someone has run a single long strip of metal up the side instead, it is wrong and it will leak.

Counter flashing. Metal let into a groove cut in the mortar joint, folded down over the step flashing. The groove is called a reglet. Counter flashing that has simply been sealed to the face of the brick with caulk instead of let into a groove is the most common bad repair in roofing.

The crown. The sloped concrete cap on top of the masonry, not the metal cap over the flue. It should slope, overhang the brick, and have a drip edge. Cracked crowns let water straight into the chimney's core.

The masonry itself. Brick above the roofline takes weather on all sides and no warmth from the house. Failed mortar joints absorb water, and in freeze-thaw climates it spalls the brick face off.

A roofer who says "it needs flashing" without saying which of these is guessing.

Caulk is not flashing

The cheap repair is a tube of sealant around the join. It works for a season or two, then fails, and the next person's repair is on top of it.

Sealant belongs at the top edge of counter flashing as a secondary measure. It does not belong as the waterproofing. If a quote is under $200 and the method is "reseal", understand that you are buying time rather than a repair.

The tell that it has been done repeatedly: layers of hardened, cracked black sealant around the chimney base. That chimney needs the flashing rebuilt properly, and everything on top of it removed first.

Why the stain is nowhere near the chimney

Water entering at the chimney runs along the top of a rafter until it finds something to drip off — a nail, a joint in the sheathing, a light fitting. A ceiling stain in the middle of a bedroom regularly traces back to a chimney twenty feet away and two feet higher.

This is why leak diagnosis is charged for and why "it can't be the chimney, the stain is over there" is wrong more often than not.

Do it with the roof

Flashing is woven into the shingles. Replacing it properly on an existing roof means lifting and reinstating courses around the chimney; doing it during a re-roof means it is simply part of the job.

So: if the roof is being replaced, insist the chimney flashing is replaced too, not reused. Reusing old flashing on a new roof is a corner that gets cut, and it puts a fifteen-year-old failure point in the middle of a new roof.

Frequently asked questions

How do I know it is the chimney and not something else?

Have someone run a hose on the roof above the chimney for ten minutes while another person watches the attic. Start below the chimney and work up. It is slow and it is definitive, and any competent roofer will do it rather than guess.

Can I do this myself?

Resealing, maybe. Step and counter flashing, no: it means cutting a reglet into mortar, weaving metal into shingle courses in the right order, and getting the sequence right the first time. It is skilled work and it is on a roof beside a chimney.

What is a cricket, and do I need one?

A small ridged structure built behind a chimney to divert water around it rather than let it pond against the back face. Code requires one on chimneys wider than 30 inches, and they are a good idea below that. $300 to $1,500.

My chimney is unused. Can I just remove it?

Yes, and it is often the cheapest permanent answer. Taking it down to below the roofline and roofing over costs $1,000 to $3,000 and removes the leak, the repointing and the annual inspection at once. Check first that nothing else vents into it.

Should the brick be waterproofed?

A breathable siloxane treatment on porous brick above the roofline costs $300 to $800 and helps in freeze-thaw climates. Never use a film-forming sealer: it traps moisture inside the brick and accelerates spalling.