“I can tell you what the problem with window installation is in one word,” says engineer Alan Mooney: “skill.” Or lack thereof, as the case has long been with windows.

As president of Portland, Maine–based Criterium Engineers, Mooney can tick off tale after tale of window woes resulting from improper installation. “In relatively new houses, owners had leaks around windows,” Mooney relays. “We took the siding off and found that the normal flashing put around windows was never installed. ... I've actually seen windows fall out of walls when the house's siding was removed.”

Mooney doesn't think new window technology will change the problems with installation. “We love to hear manufacturers talk about new technology—there truly are advancements—but the interface between the window and building hasn't changed. That's where it breaks down,” he says. “On jobsites, I see quality windows completely installed, yet the head flashing is still sitting in the box.”

Betsy Petitt, principal of Boston-based Building Sciences Corp., agrees. She thinks the major problem with window installation is flashing. “Because houses are being built so tightly, it's more important that you flash a window properly than it has been in the past,” she says.

When drafty older houses sprouted leaks, the air flowing back and forth through the walls would dry the water, preventing mold or deterioration. “People jump to the conclusion that a too-tight building is bad,” Petitt says. “But it's like the saying, ‘You can never be too rich or too thin'; it's the same with buildings. The issue is stopping uncontrolled air loss because when you lose conditioned air, it is hard on pocketbooks and the environment.”

Her solution? Flash the windows correctly and put a pan under the windows, so that if they do leak, the water will be contained.

Helping to bridge the installation information gap is Chicago-based AAMA (American Architectural Manufacturers Association), with its InstallationMasters window installers' program, a nationwide training and certification program that teaches proper installation as defined in ASTM E 2112. The program was recently endorsed by the American Subcontractors Association of Alexandria, Va.

Larry Livermore, program manager for AAMA's InstallationMasters course, provides a sort of Cliffs Notes to the AAMA training he oversees. His five points will point the way to fewer callbacks for troublesome windows.

1. Modify the Building Wrap. Alter the building wrap (or weather barrier) so that it will integrate properly with the flashing and the window. The alteration is known as a "modified I". Cut the wrap as shown, fold, and staple it to the interior. Create an additional flap at the top of the wrap. Raise this flap up and out of the way to allow for proper integration with the flashing and window head later.

2. Properly Integrate the Flashing. Make sure all the materials are installed in "weatherboard fashion". This means that the upper course of paper or flashing always overlaps the course below. The head flashing should overlap the jamb flashing, which should overlap the sill flashing. Each course of material, whether it is the flashing, window, or building wrap, must be properly integrated into the building envelope based on this concept. This directs the water out of the building.

3. Select the Right Sealant. The proper selection and use of sealant is critical to good installation. Base your sealant selection on the compatibility of the materials it comes into contact with and on how much movement is anticipated. Apply a continuous bead of sealant, approximately 3/8 inch in diameter behind the mounting flange, before installing the window. Place the sealant in line with pre-punched attachment holes or slots in the flange to restrict water penetration.

4. Set the Window Plumb, Level, Square, and True. Although it sounds elementary, this is critical to proper performance of the window and is often overlooked. A window set out of level may lead to water penetration. A window that is not set plumb, level, square, and true may not operate properly and may let in excess air. Always check and re-check the window as it is being installed.

5. Perform a Final Operation Check. After the window is properly secured into position, check its operation. This step will help you avoid callbacks due to improper function and water/air infiltration. In addition, check the manufacturer's installation instructions for directions regarding additional anchor requirements at hinge and locking points.

Window Installer 101: A 360-page training manual ($65) and a 100-minute video ($49) are available through AAMA. For more information on materials and training, visit AAMA Installation-Masters at www.aamainstallationmasters.com or contact Larry Livermore at 540-877-9957 or via e-mail at lblaama@visuallink.com.