Cast-in-place liner vs flashing repair

Cast-in-place lining and flashing repair are frequently quoted for the same complaint — a chimney that leaks — and they address different things entirely. The lining rebuilds the flue. The flashing seals the roof-line joint at $400 to $1,500. When water is the symptom, flashing is the more likely cause by a wide margin.

Two systems, two symptom sets

The flue is the passage that carries combustion gases out of the building. Its failure shows as venting symptoms: poor draught, smoke spillage, corrosion on metal parts, or a camera finding of cracked tile.

Flashing is the metal system that seals the joint between the chimney and the roof. Its failure shows as water: staining on the chimney breast, damp masonry below the roof line, a leak that appears in wind-driven rain.

One is a venting system. The other is part of the building envelope. A leak belongs to the second.

That distinction is not academic. It determines which trade you call, which permit may be needed, and which price band applies. Calling a liner company for a roof-line leak is how a $1,500 flashing repair becomes a $4,000 lining that does not stop the water.

Head to head

Why the confusion happens.

A leak is alarming, and the word attached to it is “chimney”. A contractor who sells liners may diagnose a liner, and a roofer may diagnose flashing. Both answers sound plausible to a homeowner standing in a damp hallway.

The timing of the leak resolves it.

Only in wind-driven rain: flashing, because wind pushes water sideways into a joint gravity would not reach.

In any heavy rain, tracking down the stack: the crown.

In any rain, with a damp flue top: a missing cap.

With the appliance running, and accompanied by draught problems: the flue.

What each repair involves, and why the confusion happens

Flashing repair removes the old metal, cuts a reglet into the masonry for the counter-flashing, weaves step flashing into the shingles, and seals the joint. It is roof-line work.

Cast-in-place lining cleans and prepares the flue, installs a form, places the lining material, cures it, and reconnects the appliance. It is venting work across more than one visit.

Neither scope includes the other, and neither trade should be performing the other’s work.

Cost of doing both

Flashing at $400 to $1,500. Crown at $400 to $1,500 if the top is also failing. Cap at $150 to $600. Cast-in-place lining, priced per job above the stainless band of $1,500 to $4,000.

The water work at $950 to $3,600 is the part that stops the masonry deteriorating. The lining is the part that restores the flue.

There is also a sequencing cost that does not appear on either quote. A lining installed before the flashing is repaired has to be worked around when the flashing is eventually fixed, and the roof-line work becomes more awkward and more expensive.

What the inspection establishes, and where the trades divide

A camera inspection at $150 to $800 should report on both systems separately.

On the masonry side: joint condition, spalled units, crown, cap, and flashing.

On the flue side: liner type and condition, gaps, and whether the flue suits the appliance.

Ask for photographs and a written statement on whether the appliance can be used pending repair. That report is what makes a quote testable.

Where the trades divide.

A roofer or mason repairs flashing, rebuilds a crown, resets a cap, and repoints joints.

A roofer or mason should not alter flue sizing, install a lining, or change an appliance connection.

Those decisions depend on the appliance’s listed venting requirements and local code, and they belong to a qualified chimney technician. A cast-in-place lining specified by a roofer is a red flag worth asking about.

What neither repair does

Neither replaces spalled brick. Where faces have gone, the units have to be replaced, and pointing around them is cosmetic.

Neither repairs a structural lean, which needs an engineer’s assessment.

Neither substitutes for the other: a lining will not stop a roof-line leak, and new flashing will not make a failed flue safe.

The sequence that avoids waste

1. Note when the leak appears, and photograph it.
2. Book an inspection covering masonry, flashing, and flue.
3. Fix the water path: flashing, crown, or cap.
4. Repoint eroded joints at $400 to $1,500 if the brick is sound.
5. Line the flue only if the assessment calls for it.

Step 3 protects steps 4 and 5. Water entering at the roof line will undermine any masonry repair and keep the structure around a new lining wet.

The honest summary, in five steps

1. Note when the leak appears and photograph it with a date.
2. Book an inspection that covers masonry, flashing, and flue.
3. Fix the water path: flashing, crown, or cap.
4. Repoint eroded joints if the brick is sound.
5. Line the flue only if the camera inspection calls for it.

A leak is a water question first. Flashing at $400 to $1,500 and a crown at $400 to $1,500 address almost every chimney leak.

A cast-in-place lining is the answer when the flue itself has failed, and it should follow an inspection rather than replace one.

Our flashing repair cost page covers the roof line, cast-in-place liner cost covers the flue, and chimney leak repair sets out the water paths in order.