Most houses are built today with vinyl windows. Don't get me wrong - vinyl windows are great products. They are energy efficient, relatively inexpensive, recyclable, and require little maintenance. But vinyl windows have some inherent problems that must be correctly addressed during installation.

Installation Damage

20% of new windows may leak because of damage that occurs when the window is handled and installed. Unfortunately, you can't see this damage. Vinyl windows are especially vulnerable because the corners of the window frame are "fused" together on many brands. During shipping, handling, or installation, the seal at the corner can break.

Improper Installation

We used to slam new windows into houses with little regard for water intrusion other than squirting some caulking around it. Have you ever looked closely at a typical vinyl window? A fin extends from the edge of the frame all around the perimeter. This fin extends over the edge of the opening in the wall. But it's not very wide. On most windows the fin is less than 1-1/2 inches wide, with holes in it for fastening. So it is really a mounting flange. It is not really sealing out much moisture.

Water can travel horizontally where building wrap, siding, and flashing overlap vertically on a wall. Therefore, you need wide flashing to prevent leaks.

The window industry has come up with the solution: a more stringent installation standard for the person installing the window. The new standard says you must flash around the window when it is installed, using specific steps.

The flashing must be at least nine inches wide and sealed to the window fin on the top, bottom and sides. The idea is to create a nine-inch-wide waterproof flashing around the window.

In addition, the flashing at the bottom of the window extends into the rough opening to protect the framing and finish materials inside, should the window frame leak. Ideally, a sill pan should be installed at the bottom.

The window installer must follow the window manufacturer instructions. To get an idea of the details required to properly install flanged windows, see our online instructions for one method (A1) at http://qcfocus.com/journal-article/window-flashing-instructions.

How do you know if a window has been installed properly?

1. Be there when the windows are installed.
2. Ask the builder to expose the bottom corner of one window so the flashing can be inspected.
3. Ask for an extended warranty on the window installation for leaks, if the builder cannot give you confidence that it was installed properly.
4. Look for evidence of moisture or moisture damage around the interior surfaces adjacent to all windows. Also, look on the floor below the window.
5. Ask the builder if your windows were installed by a Certified InstallationMaster ™ installer.

Advice for Homebuilders

1. Inspect all window flashing details before the wall cladding material is installed.
2. Make sure that the windows are installed according to the window manufacturer instructions.
3. Encourage your window installation workers and subcontractors to become Certified InstallationMaster™ (a program endorsed by the AAMA, American Architectural Manufacturers Association).
4. Consider using a specialty contractor to install windows instead of the framer.