Chimney flashing leaks: what the repair looks like start to finish

When water shows up on the ceiling near a fireplace, most people blame the chimney itself. Usually the chimney is fine. The trouble is a few inches of thin metal where the masonry meets the roof, and the way water behaves around it. Chimney flashing is one of the most common sources of leaks in older New England homes, and it is also one of the more satisfying things to fix when it is done right. Here is why it fails and what a good repair looks like.

What flashing actually does

A chimney punches through the roof, which creates a seam that water would love to find. Flashing is the layered metal system that closes that seam. Pieces tuck up under the shingles, climb the chimney, and are sealed into the masonry. On the uphill side there is often a small peaked section called a cricket that sheds water around the chimney instead of letting it pile up behind it. Done properly, the pieces overlap like fish scales so water always runs over the next piece, never behind it.

Why it fails

• Sealant used as the main defense. Caulk dries, cracks and pulls away through repeated freezing and thawing, and it was never meant to be the only barrier.
• Metal that has rusted, bent or lifted over the years
• Mortar joints where the flashing is set into the brick that have crumbled
• A missing or undersized cricket behind a wide chimney, so snow and meltwater stack up
• Shingle work done around the chimney that did not integrate with the flashing

Our weather is hard on this detail. Heavy snow sits against the chimney, melts, refreezes and moves the metal a little every cycle. After a few decades, small gaps open that are easy to miss from the ground.

Early signs worth checking

Stains on the ceiling or wall near the chimney are the obvious one. Less obvious are a damp smell in the attic on rainy days, discolored rafters or sheathing around the chimney, rust streaks on the brick, and a hearth that smells musty after a storm. From the yard, look for flashing that sits proud of the roof, visible gaps along the brick, or heavy gobs of old roofing cement. Do not climb up to look. A roof in wet or icy conditions is no place for a homeowner.

What a proper repair includes

The best chimney flashing jobs start before anyone touches the roof. The contractor looks at the damage with you, shows you where the water is getting in, and explains the plan. That conversation is worth a lot. A walk-through before the work tells you exactly what is wrong. A walk-through after the work lets you see what was done and ask questions while everything is still open to view.

• Remove the old flashing and any failed sealant, and check the surrounding shingles and decking for water damage
• Inspect the masonry joints and repoint or repair what needs it before new metal goes in
• Install new step flashing in layers with the shingles so each piece sheds onto the next
• Add counter flashing set into the mortar joints, not just smeared on the surface
• Build or correct the cricket when the chimney is wide enough to need one
• Tie the new work back into the roof so water has one clear path off

If decking underneath has rotted, it needs to be repaired too. Flashing screwed into soft wood will not hold, and the leak will return.

Why the walk-through matters

A lot of home repair is invisible once it is finished. The metal gets covered, the shingles go down, and you are asked to trust that it was done right. A before-and-after walk-through changes that. You see the problem, you see the fix, and you understand your own roof a little better. It also keeps everyone honest in a good way, because the work is going to be looked at.

Timing and weather

Chimney flashing is usually a bounded job, not a multi-week project, which means it can often be done on a dry day without waiting for a major season. If you have an active leak, tell the roofer so it can be handled promptly. If water is already inside, dry out the area and watch for mold in the following weeks.

Who does this at JMP

Chimney flashing is part of the roofing work JMP Construction Corp. of Leominster handles, and the company offers a walk-through with you both before and after the job. Jay, the owner, is present on the job sites. If you are noticing stains, smells or drips near your chimney, call (978) 235-4746 for a free estimate. You can also find the roofing details on the roofing page of this site, or use the contact page to send a few photos and a description of what you are seeing.