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Chimney Flashing

The chimney flashing is a common point of failure with a chimney.  They are a major cause of leaking around the roof.
Chimney flashing is the metal sheet that fits between the roof and the chimney and makes a watertight seal.  Quality installed flashing has two layers.  One layer is known as step flashing.  They are basically pieces of metal layered within one another and fitted snug against the chimney.  The counter flashing is the second piece.  This is a piece of metal that is installed and fixed in the mortar joints and pushed down to overlay on the step flashing.

Different metals can be found in flashing, depending on the region of the country and what kind of quality the builders need.  Aluminum and galvanized metal are popular choices as they are reasonably priced and are fairly weather resistant.  Copper can also be used, although it is more expensive.  The advantage with copper is that its corners can be welted shut.  Lead flashing is more popular in the northern regions.  Lead is easier to shape than other metals.

The main failure points are at the corners, where the metal can be difficult to work with.  Even professional installations will be left with a small spot.  This will require a good quality urethane caulk in order to seal it.  However, as with most caulks, it can wear out over seasons of weathering.  In many instances recaulking will fix the issue.  However, if the flashing installation itself is the issue, greater steps may need to happen.

Many professional installers will add a cricket.  A cricket is a diversionary roof that is installed at the base of a chimneys connection to the roof.  They are especially beneficial when the chimney is attached to the bottom of the roof and so they deflect a direct stream of water runoff from the top of the roof.  A professional roofer can blend this in so it looks like part of the roof.
Your chimney flashing should be inspected every year or two for signs of trouble.  A little caulk may be all that’s need to repair any issues with the metal, but if you’re not sure, call a professional.


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