During heavy rainstorms, many homeowners find out the hard way that their home is not as waterproof as it needs to be. There are many places where wear and tear can chip away at your roofing and allow for water leaks during heavy rains. However, many times the roof chimney is overlooked when it is in fact a very common source for leaks. Leaks in the chimney around the roof can occur in two ways: cracked or loose bricks that allows water to seep through, or improper flashing around the chimney. In the first case, channels, cracks, or crevices in the mortar allow water to move from the outside roof portion of the chimney to the inside part in your home. Although a tiny crack may seem like it cannot hold much water, all of them together can absorb gallons of water during a long rainstorm. Brick laying should be done by an expert who should use hydraulic cement for mortar. Unlike regular mortar, hydraulic mortar is non-porous. But if you don’t want to rebuild your entire chimney, you can cover the top of the chimney with a lead coated copper sheet cover to prevent leaks. Improper or worn flashing around a chimney along the roof is the most common source for leaks. A hairline crack above the flashing  is all it takes to allow a vast amount of water to pour into your home during heavy rains. Flashing can be worn, or corroded over time. Aluminum flashing tends to wear fastest, lasting about 5 years. Your flashing might also be improperly installed. Flashing should not just be glued to the brick, there should be a stepped flash or counter flash slipped into a one inch slot. Whatever you do, do not use caulk to repair flashings and instead use a high pressure polyurethane sealant. You can test the resistance of your flashing by running a low pressure hose around the chimney to roof intersection and see if any water comes inside. Most importantly, be proactive and don’t wait until you have a leak to find out where it is coming from. Chimney leaks can deposit water in your ceilings and walls where mold can be devilishly hard to deal with. All it takes is one big rain.