What is Window Flashing?

Window flashing is a thin, waterproof material that goes around your window’s rough opening. 

While not as exciting as purchasing new windows or picking a frame material, flashing is integral to the installation process. Without it, water can enter your home, and the frame can rot.

If you’re gearing up to order or replace windows, here’s what you need to know about flashing.

Types of Window Flashing

window flashing

Most windows require flashing, and some building codes require a specific type. Flashing is not a project to skimp on or DIY if you don’t have previous experience. Improper flashing installation is a top cause of window leaks.

There are three main types of flashing: sheet metal, tape/self-adhering, and vinyl.

1. Sheet Metal Flashing

Sheet metal flashing includes aluminum, stainless steel, copper, and zinc. These materials come in thin, flexible sheets and are often a go-to for brick and stucco houses.

2. Flashing Tape or Self Adhering Window Flashing

Self-adhering flashing is standard for new construction and replacement windows. It comes in rolls like tape, making it easy to apply. 

Most self-adhesive flashings have a rubberized asphalt core which acts as a moisture barrier.

3. Vinyl Window Flashing

Vinyl window flashing is a top choice for homes with vinyl siding and windows. Vinyl is a durable material that does well in moderate climates. The big downside is that it can crack in extreme cold.

How Window Flashing is Installed

Flashing installation depends on the window material, siding material, type of window, and local building codes.

For example, in some areas, you can affix building wrap or felt around the frame and install a drip cap, which acts like a canopy directing water away from the house. In other areas, building codes require higher quality flashing to protect the home better.

But no matter the method, flashing must be installed in a particular order, depending on the window manufacturer.

In general, you or your contractor must install flashing in one of two ways for it to shed water:

  • Install membrane flashing in a shingle fashion where the top layer overlaps the bottom. 
  • Combine flashing with the house wrap or water-resistant barrier.

You can find more flashing guidelines from the International Residential Code here.

Window Flashing: Leave it to the Professionals

While flashing a window sounds easy, small mistakes can lead to expensive repairs. Since many variations depend on your specific home, siding, and windows, it’s best to leave this job to the pros. If you decide to do your flashing, read and follow the installation instructions from your window manufacturer.