The chimney that stopped working years ago
Almost every older house here has a brick chimney that no longer carries anything. The furnace was changed, the fireplace was closed, and the chimney quietly became a decorative object that still puts a hole through the roof.
- 1 The ridge. One ridge over two households, and one of them pays to replace it.
- 2 The field. The part everyone looks at, and rarely the part that actually failed.
- 3 Valleys. Most of them were cut in later, when the house was divided into flats.
- 4 The chimney. Often two of them, and often neither one carries anything any more.
- 5 Penetrations. Two kitchens and two bathrooms mean twice the holes on the same roof.
- 6 The overhang. Where heat from a flat you do not control comes back down as ice.
Why an unused chimney leaks more, not less
A chimney in use is warm and dry inside. One that carries nothing is cold, and it takes in water at the top and through the joints, then holds it. Freeze and thaw do the rest to the mortar, year after year.
And because nobody uses it, nobody looks at it. The crown cracks, the cap goes missing, the flashing loosens, and the first anyone knows is a stain on a ceiling in a room nowhere near the chimney.
The flashing is a two-trade job
A chimney needs metal worked into the masonry itself — let into a joint and pointed back in — and lapped over the covering below. That is masonry work done by a roofer, and plenty of crews will surface-mount the metal and seal it instead.
Ask directly: is the counterflashing let into the brick, or fastened to the face of it? Those are two different prices and roughly a decade apart in service.
The question worth asking during a re-roof
If the chimney carries nothing and never will, taking it down to the roof line and closing the hole properly removes a maintenance item permanently. It is not always the right answer — the brick may be structural, or the owner may want it — but it should be on the table before a new roof is built around it.
The one thing not to do is nothing. A new covering around an old chimney will leak at the chimney, and the roof will be blamed.