Flashings are critical to soundness of home — Chicago Tribune

Flashings are critical to soundness of home - Chicago Tribune

DEAR TIM: I’m looking at bids right now for a re-roof project and a new deck job at my home. The bid documents mention flashings. I have no clue what they are and whether or not they’re important. If they are important, what should I know to ensure they’re installed correctly? —Ally T. Philadelphia

But what happens when something interrupts the shingles, siding, brick, stone or any other exterior finish that’s meant to keep water from inside your home? At such a location you need a flashing to make sure the water continues on its journey to the ground and doesn’t take a detour inside your house.

A flashing is a waterproof material that diverts or redirects water to a point lower on the outer face of a building. Think of a flashing as a transitional building material. It connects something that is waterproof to something that’s not. I realize this is confusing, so I’ll give you some examples.

You’ll often discover a metal flashing surrounding a skylight in a roof. The flashing is often made of pieces of bent metal that lay under and over shingles, going up the sides of the skylight and connecting to the top of the skylight in such a way that driving rain can’t leak into your home.

You’ll discover flashing where a roof butts up against a wall of a house or where a chimney is popping up through a roof or next to a roof. The flashing can be made from galvanized steel, tin-coated steel, lead, copper or even a rubber membrane.

Flashings are mission critical in brick or stone-veneer construction. Water readily leaks through brick and stone veneer and must be captured by flashings you can’t see behind the brick or stone. This water is then redirected to the exterior of the building via weep holes.

Great builders install flashings on top of windows and doors. The water streaming down a wall would love to get behind the window or door. The flashing on top prevents this from happening and sends the water streaming across the front of the window or door so it can get to the ground.

Installing flashings is an art and craft. I’ve seen countless poor installations in my time. When I was a young carpenter and builder, I had the good fortune to work on many an old home built in the early 1900s. I studied and copied the flashings I would see on chimneys, dormers and old-fashioned box gutters. Many were built and fabricated by true craftsman.

It didn’t take long to see how the seams were formed and how the flashings were constructed to guide the water so it continued its journey to the ground. One thing I noticed right away is that flashings always had a slope built in so water never ponded on them. Gravity always pulled water down or off the flashing to the building material just below the flashings.

Flashing materials almost always need to be cut and bent. Any seam in a flashing must be made waterproof. When you use galvanized metal, tin-coated steel, copper or lead, you can solder these seams to create a waterproof seal. Rubber membranes come with special solvents that allow you to weld to pieces of rubber together.

Never, ever rely on caulk as a permanent sealant for a flashing. It’s not uncommon for flashings to last 50 or more years. I’ve never seen a caulk that can last for that long, but solder does.

Beware of using aluminum as a flashing material in contact with masonry. The chemicals in the mortar can corrode the aluminum, causing leaks.

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