Some people regard flashing as deviant behavior. We, on the other hand, view it as a necessary element of construction. Flashing is a means of preventing water from making its way into areas of a building that could result in a leak. And where there is a leak, damage usually follows. Whereas flashing can be found in many locations throughout a home (foundation, steps, decking, etc.), it is used predominantly on the roof. In fact, many roof leaks haven't anything to do with roofing material. More often than not, they are the result of faulty, nonexistent or poorly installed flashing.
Most modern flashing is constructed of galvanized sheet metal, but copper, lead, asphalt, plastic and other flexible waterproof materials can also be used. Flashing typically can be found around a chimney where it meets the roof, in valleys where two rooflines come together, at a wall-to-roof connection, by the eaves and where plumbing vents and the flues for mechanical systems exit the roof.
There are several reasons why flashing and/or a flashing system will fail. For example, a flashing system that integrates the use of an asphalt compound or caulking material will fail after prolonged exposure to the elements. Ultraviolet rays from the sun will deplete these products of their elasticity and will result in cracking and delamination.
Consequently, these materials must, from time to time, be replaced. The same holds true for the counter flashing that surrounds a brick chimney. The mortar joint into which the counter flashing is embedded might eventually be the source of a leak as the mortar joint gives way to freeze/thaw cycles. Sealing the brick with a high-quality waterproofing material can prevent this from occurring.
One of the biggest threats to metal flashing is rust. Keeping flashing material free of debris will help keep flashings dry and, in turn, prevent rust. If rust should occur, tackle it with a wire brush and a rust solvent. Once clean, the affected area should be spot-primed with rust-inhibiting metal primer and finished with a paint to match that which currently exists.
The big mistake that most folks make is to wait for Mother Nature to determine if their flashings are leaking with the first winter's rain. The best time to check for leaks is in the fall before the rainy season. All you need is a sturdy ladder, rubber soled shoes, and a garden hose. Caution: walking on the roof can be dangerous and can cause damage to the roofing material. If you are afraid of heights or have not walked on your roof before, you might want to have someone else perform the water test for you. If you are up for the challenge and aren't sure where to walk on the roof, consult a roofing contractor for advice, as the best location to set foot varies from type to type.
Two people best perform the leak detection process, one on the roof with a garden hose and the other in the attic (or inside the house, if no attic exists) to spot the leak. A pair of inexpensive walkie-talkies can enhance communication.
Start by testing flashings at the lowest point on the roof. Direct the garden hose with medium to low flow at the area where the flashing meets the roof. When it comes to flashing around vent pipes, pay special attention to the joint between the flashing and the vent pipe, called the "collar." Often, the collar is coated with an asphalt material or consists of neoprene, both of which can become brittle with prolonged exposure to the sun. Wrapping the joint with duct tape or making a patch with roofing cement are temporary fixes. The flashing should be replaced with a new one.
The chimney is another prime location for flashing failure. Most chimney flashing consists of a two-part system - the "L-shaped" flashing that abuts the roof and the chimney and the counter flashing or "cap shield" that covers the piece facing the chimney. Ideally, the counter flashing should contain a small 90-degree bend at the top that is embedded into the mortar joint between layers of brick. Often, however, the joint is simply smeared with an asphalt roofing compound or caulked - both methods of which are temporary, at best. The longest-lasting fix is to remove the existing counter flashing and replace it with new material that is embedded into the mortar joint.
There is yet another reason why the chimney is a primary source of flashing leaks, its independence. While this isn't true with modern zero clearance models, traditional brick fireplaces and chimneys are so heavy that they require their own foundation. Consequently, the fireplace and chimney can move at a different rate than the roof and the rest of the home. The location becomes sort of a push me pull you, and results in a tear.
The low side of the chimney should be water tested, first working your way up to the high side and then to the counter flashing.
Finally, when it comes time to re-roof your home, insist on new flashings everywhere: chimney, valley, plumbing, etc. Trying to save a few bucks by reusing the old flashings can end up costing you dearly in the long run.
