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How to Repair Leaking Roof Flashing Around a Chimney or Vent

Time required: 1-2 hours · Difficulty 3/5

Roof work carries a serious fall risk, and improperly resealed flashing can cause hidden leaks that lead to rot and mold — some insurers treat this as a pre-existing maintenance issue rather than a covered loss. Only attempt this on a dry day, on a roof with a shallow, walkable pitch, using a roof harness. If your roof is steep, wet, or more than one story, hire a licensed roofer.

Est. DIY Parts: $15 - $25 · Pro Service: $250 - $450 · Est. Savings: $225 - $430

* Estimates based on regional/national contractor rate benchmarks. Actual part prices vary by brand and retailer.

Parts & Tools You'll Need

Step-by-Step Manual

  1. Set up fall protection and inspect from the ground first Put on your roof harness and anchor it before climbing. Use binoculars from the ground first to identify the exact section of lifted or cracked flashing.
  2. Clear debris and scrape old sealant Remove leaves and grit from the gap between the flashing and the chimney/vent, then scrape away any cracked, hardened old caulk or cement.
  3. Re-nail any lifted flashing If a section of metal flashing has pulled loose, re-nail it flat against the roof deck with galvanized roofing nails.
  4. Apply roofing cement to the seam Trowel a generous layer of roofing cement along the joint between the flashing and the chimney or vent pipe, covering all nail heads and gaps.
  5. Smooth and feather the edges Smooth the cement with a putty knife so it feathers into the surrounding shingles without leaving a thick ridge that could trap water.
  6. Let it cure and hose-test Allow the cement to skin over per the label (usually a few hours), then run a garden hose over the area for 5 minutes and check the attic below for any drips.

Frequently Asked Questions

What are the signs of leaking roof flashing?

Water stains on the ceiling or attic wood near a chimney, vent, or skylight are the most common sign. On the roof, look for flashing that is lifted, rusted, cracked, or missing nails, and for old sealant that has dried out and pulled away.

Can I fix leaking flashing with roofing sealant?

Roofing cement or sealant can stop a small leak at a seam, which is what this guide covers. It's a short-term fix. If the metal flashing itself is rusted through, torn, or badly bent, it should be replaced, usually by a roofer.

When should I call a roofer for a flashing leak?

Call a licensed roofer if the roof is steep, wet, or more than one story, if the flashing metal is damaged, if the chimney mortar is crumbling, or if the leak continues after resealing.

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