Why does a chimney leak even when the flashing looks fine?
Water can come through cracked mortar, a damaged crown or the brick itself, which absorbs rain. Flashing that looks intact can also be lapped incorrectly, or installed over rotted decking. A roofer checks the metal, the masonry and the deck before deciding where the leak starts.
Brick and mortar are porous. In a wet year they hold water, and in a freeze they crack. A hairline in the mortar above the roof line may admit more water than a visible gap in the flashing.
A mason and a roofer may both be needed. The roofer should tell you plainly which part of the problem is theirs and which is not.
What is a chimney saddle and does mine need one?
A saddle, also called a cricket, is a small ridge built behind a chimney on the uphill side. It divides water and snow so they flow around the chimney instead of piling against it. Wide chimneys are the ones that most often need a saddle.
A narrow chimney sheds water easily; a wide one acts like a dam. Snow collects behind it, melts slowly and tests the flashing for longer.
If your chimney is on the downhill side of a slope or is wide, ask the roofer whether one is present or advisable.
Can chimney flashing be repaired without removing shingles?
Sometimes small sealant repairs are possible, but proper flashing is woven into the shingle courses, so a lasting repair usually means lifting the shingles around the base. The roofer should explain what is planned and what the shingles will look like afterward.
If the surrounding shingles are old and brittle, lifting them may break them. This is a good moment to ask whether a larger repair or a section replacement makes more sense.
A roofer who shows photographs of what is under the shingles gives you the information to decide.
How do winter conditions affect a chimney joint?
Moisture in cracks freezes and expands, widening gaps in mortar and sealant. Snow piled against the uphill side melts slowly and sits against the flashing. In a county with 30 to 40 inches of snow a year, the joint is under stress for months.
Spring is when a winter's damage shows. A chimney that was dry in October can drip after a thaw, and the fix is often at the flashing or mortar.
Ask the roofer whether the repair is suited to cold weather or should be done when it is milder, and what a temporary measure would involve.
Should I repair the flashing, the mortar or both?
Often both, since water entering at either place reaches the same ceiling. Resealing flashing without sound mortar can leave a leak behind the metal, and repointing without good flashing leaves the roof-line joint open. A roofer and a mason can split the job between them.
The sequence matters. Masonry repairs are usually done first, because new counter flashing is set into the mortar joints, and it should go into sound material.
Ask for the work to be written as two items if two trades are involved, so you know who is responsible for which part and can hold each to their own scope.
