The majority of calls that we receive are about chimney leaks. And by and large, the cause of the problem is the waterproof sheet metal flashing between the roof and chimney. If it is faulty and water gets through, it can greatly damage the ceiling, roof sheathing and framing below. It is therefore imperative that you correct this problem right away.
A correctly-installed chimney flashing comprises of two layers. The first layer is known as step-flashing, where parts of sheet metal with an L-shape are interwoven in the courses of the shingle and folded up on the chimney side. After this comes the counter flashing, where another metal layer is imbedded in the mortar joints of the chimney and lapped downwards to conceal the topmost section of the step flashing.
The corner sections are particularly exposed. We cut and twist the metal all round the corner. But no matter the quality of the installation, there is always one tiny spot left that requires to be sealed using high-grade urethane caulk. However, the caulk might loosen itself with time. Recaulking should correct the problem if the flashing seems to be in great condition. But caulk should not be an alternative to correctly overlapped flashing materials.
Where you reside affects the type of metal that is used for flashing. In the South, galvanized steel and aluminum are the most commonly-used materials. Even though copper is the most durable metal when it comes to flashing, it is only used for upmarket jobs because it is costly. Another strongpoint of using copper is that you can solder the corners in order to get a waterproof connection. Masons in the Northeast prefer lead flashing because it is soft and pliable. But irrespective of the material that is used, the flashing has to be layered in the right manner to ensure that it is watertight.
If the chimney is set at the lowermost part of a roof slope, we ensure that we have installed a cricket at all times. A cricket is a small structure installed where the roof slope meets the chimney, and it is designed to divert water away so it does not cause leakages around the chimney. The crickets are framed and encased like the other parts of the roof. A modified bitumen membrane is then used to cover them completely before it is folded beneath the chimney flashing. To make sure that the cricket blends with the other sections of the roof, we cover the membrane using asphalt shingles.
Since chimneys are common sources of problems, it is essential that they are checked for cracks in the masonry or missing or loose flashing after every one or two years. Masonry caulking can be used to seal small cracks. It is also advisable for homeowners to make their brick chimneys watertight at least once every couple of years by using a garden sprayer to apply a silicone-based sealer. Even though some builders may disagree, this is good way of stopping water from penetrating into the brickwork.