Metal flashing can save your home from rot

BY TIM CARTER Tribune Media Services

The reason ducks and birds stay dry is because the way feathers overlap one another. Water can’t get under the feathers to the duck’s skin. That keeps them warm and dry. That’s where the idiom “like water off a duck’s back” comes from.

DEAR TIM: My builder is talking about installing metal flashing as he’s putting up my vinyl siding. What in the world is this material and why is it necessary? Some other people I’ve talked with have no idea what it is and feel it’s not necessary. I don’t want to waste money, so can you tell me all you can about flashing and if you would use it when building homes? —Tara P.

DEAR TARA: Oh gosh, I don’t have near the space here to tell you everything I know about flashings of all types. My guess is I could write two or three small books to cover much of the topic. Suffice it to say that flashings have been around for hundreds of years, and if I was in charge of the building code and the best building practices manuals, these materials would be here for a millennium or more.

Flashings are used both on exterior walls and primarily on roofs. They can be made from many materials, including tin, copper, galvanized metal, plastic, wood and lead. I describe them as a transitional material. When a flashing is used on a roof, it typically is used to transition from roofing material to something that’s not a roof. For example, you need flashing

where a skylight, chimney, dormer, plumbing vent or air vent extends up through a roof. The roofing material stops where these elements go through the roof, and something must connect them to the roof so there is no leak. That’s the job of a flashing.

In your case, with the vinyl siding, your exterior trim work has horizontal fascia boards at the bottom of the house and each story line. When the vinyl siding rests on top of these boards, a piece of flashing is needed to create a leak-proof conversion between the first piece of vinyl siding and the horizontal fascia board.

Here’s why the metal flashing is so important in your case. You have to think about how roof shingles or feathers on a duck work to get a good understanding.

The reason ducks and birds stay dry is because the way feathers overlap one another. Water can’t get under the feathers to the duck’s skin. That keeps them warm and dry. That’s where the idiom “like water off a duck’s back” comes from. Water readily flows off the duck because of the composition of the feathers and the overlapping layering.

To keep your house dry so it doesn’t rot, you need to build it the same way. This goes for exterior siding as well as roofing.

Each time you transition between materials — be it foundation, siding, brick, windows, doors or what have you — you need to make sure each material sheds water over the top of the material below without letting it behind or under the materials.

In your case, there is a great need for a flashing that runs along the top of any of the horizontal fascia boards. Metal flashing comes in many different shapes, but in your case the metal laps over the fascia board perhaps 1/4 inch, then is bent at a 90 degree angle to pass over the top of the fascia board, then is bent again at a 90 degree angle to go up the wall so that it extends behind the first row of vinyl siding.

You should be able to see how

See BUILDER, page C39