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Lead flashing on a chimney: what it does, how it ages and what to check

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Lead is soft enough to be shaped tight to brick and tough enough to last for decades. It still fails, and the failures are easy to spot from the yard.

Lead flashing on a chimney is a sheet of soft metal shaped around the base of the stack to keep rain out of the joint where brick meets roof. It does the same job as steel or aluminum flashing. The difference is how it behaves: lead bends by hand and holds its shape.

Why lead is used on chimneys

Brick is rough and never perfectly straight. A stiff metal has trouble following it. Lead can be pressed into the mortar joints and folded around corners without cracking. That is why it shows up on older homes and on chimneys with awkward shapes.

It also resists corrosion well. A lead apron can outlast the shingles around it. That does not mean it lasts forever, and it does not mean the joint around it is sound.

How lead flashing is arranged

On a chimney, lead usually works as two layers. The lower layer, the base flashing, laps under the shingles. The upper layer is turned into a mortar joint and hangs down over it. That upper layer is the cap flashing. Water runs down the brick, lands on the upper layer, and drops onto the lower one.

The sides follow the slope of the roof, which is why a chimney often shows the staircase pattern described in step flashing around a chimney.

How lead flashing fails

Lead moves a lot with temperature. Over many winters it creeps downhill and thins. The signs are slow ones.

  • Cracks or splits, usually at a fold or corner.
  • Sections that have slumped or slid down the roof.
  • Gaps where the upper edge has pulled out of the mortar joint.
  • Thick bands of sealant smeared over the top edge.
  • Pale, chalky surface with pinholes.

Sealant on lead is a warning sign, not a fix. It usually means someone saw a gap and covered it. The gap is still there, and the sealant will crack the first time the metal moves.

What you can check from the ground

Stand in the yard with binoculars and look at the base of the chimney on all four sides. Look for slumped folds, dark smears of old sealant and mortar that has fallen away above the metal. Take a photo of each side.

Inside, look at the ceiling and wall nearest the chimney. In the attic, use a flashlight and stay on the joists. Stains on the chimney framing after heavy rain point at the flashing line before they point at the shingles.

Is lead flashing worth keeping?

If it is intact, tight to the brick and tucked into sound mortar, yes. It is a good material and there is no reason to replace it for its age alone. If it is split, slumped or buried under sealant, it needs a closer look by a roofer. Ask to see the damaged section and ask what is under it.

Why we do not show the repair

Working with lead flashing means standing on the roof beside the chimney, lifting shingles and cutting into mortar joints. That is work at height on a sloped surface, and we do not publish the steps. Use the ground checks above, then have a licensed roofer explain what needs to change. If you want to compare other metals and layers, read what is roof flashing.

Frequently asked questions

What is lead flashing on a chimney?

It is soft sheet metal shaped around the base of a chimney to seal the joint with the roof. Part of it laps under the shingles and part is turned into the brick mortar joints.

Why is lead used instead of other metals?

Lead bends by hand and can be pressed tight to uneven brick without cracking. It also resists corrosion well.

How long does lead flashing last?

It can last for decades, but it slowly creeps and thins with temperature changes. Condition matters more than age.

Should I put sealant over a gap in lead flashing?

Sealant over a gap usually hides the problem rather than fixing it, because the metal keeps moving and the sealant cracks. Have a roofer find out why the gap opened.

Can I repair lead flashing myself?

We do not publish steps for it. It means working on the roof beside the chimney. Document what you see from the ground and have a roofer do it.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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