Chimney Leaking After a New Roof: Causes and Next Steps

Why reroofing disturbs the chimney joint

The joint where a chimney passes through the roof is the most complicated detail on most roofs. During a reroof, the old shingles and step flashing around the chimney come off, and new ones go on. The counter flashing in the brick above is supposed to lap over the new step flashing. If any part of that sequence is rushed, reused or skipped, water finds the gap.

Roofers and chimney contractors often each assume the other handles this joint. Roofing crews work on the roof covering; the counter flashing and masonry are part of the chimney. When nobody owns the detail, it is often patched with sealant and left.

The usual causes, most common first

When we trace leaks on chimneys that were recently reroofed, these are the causes we find most often. Several can be present at once.

• Old counter flashing reused, bent back down over new step flashing that does not fit it
• Step flashing skipped, with shingles butted to the brick and sealed with tar or caulk
• No cricket or back pan on the uphill side of a wide chimney
• Counter flashing pulled out of soft mortar joints during tear-off and not reset
• New underlayment not turned up the chimney sides
• A leak through the crown, cap or brick that existed before and was blamed on the old roof

Was the leak there before?

Not every leak after a reroof is the roofer's doing. Water entering through a cracked crown, an uncapped flue or porous brick above the roof runs down inside the chimney and can come out at the roof line, where it looks like a flashing leak. Old roofs sometimes hid this with layers of tar, or the old decking soaked it up without showing a stain. Once new decking and fresh drywall paint are in place, the same water becomes visible.

The timing helps. A leak that appears in the first heavy rain after the roof is finished, beside the chimney, points to the new flashing. A leak that shows as damp on the chimney breast inside, or water in the firebox, points to the chimney itself.

• A stain beside the chimney after the first big rain points to the new flashing or underlayment; call the roofer first
• Tar or caulk where metal flashing should be is a shortcut at the flashing; that is also the roofer's to answer
• Water in the firebox or on the damper points to the cap, crown or flue; call a chimney technician
• A damp chimney breast on upper floors points to brick, joints or the crown; that is chimney work too
• A leak only after snow suggests a missing cricket or back pan; the roofer and chimney technician should look together

Damage during tear-off

Stripping a roof is rough work around a chimney. Pry bars and shovels catch the counter flashing and pull it out of its joints, and on older chimneys with soft mortar the joint itself can crumble, so the flashing has nothing to go back into. Bricks at the roof line can be chipped or loosened. Heavy debris dropped on a flat crown can crack it.

None of this is always visible from the ground. If the leak started after the reroof and the flashing looks intact, the counter flashing joints and the brick just above the roof are the next places to look.

What to do first

Contact the roofing contractor promptly, in writing, describing when and where the leak appears, with photos of the stain and the outside of the chimney. Many roofing contracts include a workmanship period for the installation, and the roofer should be given the chance to inspect and correct their work. Keep a copy of the contract and any written terms.

In the meantime, protect the inside: buckets, plastic over insulation in the attic, and furniture moved away. Do not go on the new roof to apply sealant yourself, which can complicate any workmanship claim and rarely stops the water.

Note the date of each leak and the weather, since that pattern helps everyone find the source.

When to bring in a chimney technician

If the roofer's fix does not stop the leak, or if the evidence points above the roof line, a chimney inspection sorts out the masonry side: crown, caps, mortar joints, brick condition and the counter flashing joints. A neutral, written report with photos helps when the roofer and the homeowner disagree about the cause, because it shows exactly where water is entering.

Often the right repair needs both trades: new step flashing woven into the roof by the roofer, and counter flashing set into ground joints, repointing and crown work by the chimney crew.

What a written report should include

Whether the report comes from the roofer, a chimney technician or both, it should say where water is entering, with photos of each spot: the step flashing, the counter flashing and its joint, the back of the chimney, the crown and the caps. It should separate items that relate to the new roof from items that are chimney maintenance, and list the repair for each.

That separation is what makes the conversation with the roofer productive, and it is what an insurer or a future buyer will want to see as well.

How a proper chimney flashing detail looks

On a shingle roof, new step flashing is woven in with each course along the sides, an apron covers the low face, and a back pan or cricket handles the high side. Counter flashing is set into a groove ground into a mortar joint and lapped down over the step flashing, with sealant only in the groove. Underlayment turns up the chimney sides beneath the flashing. On a flat roof, the membrane is turned up the brick as base flashing with counter flashing above.

Wide chimneys partway down a slope often call for a cricket under many codes. A reroof is the natural time to add one.

Planning the next reroof

Before a roof replacement, ask the roofer exactly what they will do at the chimney: new step flashing, new or reused counter flashing, a cricket if needed, and how the counter flashing will be attached. Have the chimney inspected before the roof goes on, so repointing, crown work or a rebuild above the roof line can happen while the roof is open. Agreeing up front who handles each part of the joint prevents most post-reroof leaks.

Get those answers in the written contract, not just in conversation.