The bricks go up around the tile flue liners but at the top you need something to stop the rain and snow from just falling in around the tiles.
Chimney siding leak.
And more often than not the culprit is the flashing the sheet metal that keeps the intersection between the chimney and roof watertight.
Installation gaps in siding of any type if not back flashed invite leaks into the wall above left.
If the leak does show up in this area have an expert check and repair the shingles.
Apply sealant to the flashing of your brick chimney using a caulking gun.
Fixing leaks around chimneys my firm gets more calls about leaks around chimneys than about any other problem.
You can see that the very purpose of the chimney crown is to keep rain out.
Structural movement or damage shown in a more extreme case at above right can also allow significant leaks into the building.
The chimney crown is the cement part on top of the chimney.
See siding fiber cement gaps.
Before applying the new sealant to fix the leak in your brick chimney you ll need to scrape out the previous sealant using a scraper.
2 many chimney leaks are from cracks in the chimney crown.
Replace missing worn or damaged shingles in the appropriate fashion.