Restoration Guide: Windows and Doors Flashing

Barbara Marquand

Editor's Note: This is article 10 of 12 in Chapter 4: The Windows and Doors Guide of Old House Web Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development Rehab Guide.


Flashing is one of those materials that you rarely see, but plays a crucial role in keeping your old house sound. One of the longest lasting components of a building, flashing is the material installed around windows and doors on the exterior to prevent water from leaking through crevices. Installing flashing takes time and requires experience. Not sure what you're doing? Call in the experts when you encounter this important task as part of a home renovation project.

The section of the Old House Web Restoration Guide explains the purpose of flashing, materials used for flashing today, and considerations for installation.

Section 1--The Basics

Flashing must feature these key ingredients:

  • Durability
  • Weather resistance
  • Ability to accommodate movement
  • Compatibility with adjacent materials

The proper flashing system depends on the type of window or door. Traditionally, flashing materials were overlapped to adjust to movement, provide multiple layers of resistance to moisture, and prevent water from moving upward in high winds. Today, though, large sheets of membrane are often used in conjunction with new windows that come with integral nailing fins.

Most doors now are made with weather-resistant extruded metal or polycarbonate sills, which don't require flashing because they are weather resistant and are attached flush to the sub flooring. Traditional wood sills require flashing to protect the framing.

Repairing windows or doors as part of home renovation gives you the chance to check out the flashing and repair it if necessary. Sometimes removing a window can rip or poke a hole in the barrier. You can add more flashing or use a sealant to make the repair. But make sure any new materials you use are compatible with each other and the window unit to avoid a bad chemical or electrolysis reaction.

Section 2--Flashing Materials

The three main groups of flashing are:

  • Sheet metal, including aluminum, copper, zinc, and galvanized steel, among others
  • Vinyl products
  • Membrane, such as roofing underlayment, roll roofing materials, and tape products

Use sheet metal or vinyl flashing for traditional assemblies of overlapped materials. New barriers using self-adhering tape or membrane materials work with doors and windows with integral nailing fins.

2.1: Sheet Metal Flashing

Sheet metal is one of the most durable materials around. The material includes, from most to least durable:

  • Stainless steel
  • Lead
  • Terne coated copper
  • Copper
  • Galvalume
  • Galvanized steel

Remember, choose flashing materials and sealants that are compatible with one another to prevent adverse reactions. Installing sheet metal flashing requires a moderate amount of skill, and the materials accommodate most conditions. Beware that some sheet metal materials, such as stainless steel and galvanized steel, are tough to work with.

2.2: Vinyl Flashing

A relative newcomer compared to sheet metal, vinyl is compatible with widely available vinyl windows, doors, and siding. The material is easy to cut and not subject to galvanic action with other flashing or fasteners. On the downside, vinyl isn't as strong as sheet metal and might become brittle in the cold. It's also vulnerable to degradation by UV rays.

2.3: Membrane or Tape Flashing

Self-adhering membranes and tape provide a continuous barrier. These products come in large rolls or sheets to minimize seams and air infiltration and are available from makers of housewrap products and roofing materials. Even inexperienced users should find these materials fairly easy to work with. However, self-adhering membranes or tape doesn't provide multiple layers in case of failure and may be vulnerable under exposure to UV light, some sealants, and extreme heat.

For additional information on flashing materials, see the Roofs Chapter of the Old House Web Restoration Guide.

Search Improvement Project