Chimney leaks aren't as simple as you might think. Although the chimney itself could be cracked and allowing water in, there are a number of other possible culprits as well. For example, the connection between the roof and the chimney, or the two strips of flashing that protect that joint, can all become compromised and allow water into your chimney. Here are three reasons your chimney could be leaking.

1. Missing chimney cricket

Not every chimney needs a chimney cricket. However, you can predict your chimney will need one if it has a long slope of roof draining toward it, or if it has a particularly wide chimney wall that water tends to get caught behind. The cricket is like a tiny roof that sits right behind the chimney; it redirects water to drain away on either side rather than fetching up against the chimney wall.

If your chimney doesn't have one of these and a lot of water gets stuck behind the chimney, gravity can eventually form a leak in that area. Talk to your roofing contractor about whether your chimney may need a cricket installed.

2. Improperly installed flashing

Chimney flashing should be installed with two parts: one that attaches to the roof's surface and an upper part that lines the side of the chimney. These two sections overlap one another considerably in order to make sure water can't sneak through. This two-part system ensures that when expansion and contraction occur (roofing tends to expand and contract quite a bit due to changes in temperature), the roofing won't pull the flashing apart and create a leak.

The upper part has an edge that needs to be embedded into the chimney's mortar in order to keep water from sneaking behind it along the chimney's surface. If the flashing isn't embedded properly, leaks can easily form. The strip of flashing that attaches to the roof needs to be installed properly as well, or water can bypass it and enter the joint where the chimney enters the roof.

3. Chimney or flashing damage

A crack in the chimney can allow water to enter even without any roof damage. If the flashing is damaged (perhaps by hail or flying debris in a storm, or by a raccoon trying to make its way into your attic) that can also allow water to enter, even if the flashing was installed correctly in the first place. 

These are three examples of common reasons for chimney leaks. Be sure to hire a conscientious, experienced contractor to suss out what's wrong with your chimney if you're experiencing a problem.