A Look at Installation

Top window installation mistakes
Rich Rinka
August 7, 2018
COLUMN : Decoded | Codes & Standards


Example of an installation mistake in a building under construction in which flashing is only at the head and jambs. (Image by Kaitlyn Rinka.)

Installation is the determining factor of whether the performance designed into a window is realized in actual service. Even the best-designed and thoroughly tested product can fail if improperly installed. 

Experience shows that there are avoidable installation errors. The most common result of such errors is water intrusion, which can cause damage to interior finishes, promote structural rot and encourage growth of hazardous molds. Another is the inability of the window to operate as designed.

Water penetration 

To resist water penetration, the window or door frame must integrate with the exterior facing material, sheathing and the water-resistive barrier (building wrap) to form a unified, fully integrated “drainage plane,” or a constrained rainwater pathway from roof to ground. Some common water-related errors are as follows. 

• Building wrap not properly cut

The Problem: Some installers will cut and wrap the building wrap into the rough opening at the head. This can result in water following the wrap into the opening. 

The Fix: Properly executing an “I-Cut” for doors or “Modified I-Cut” for windows will result in proper drainage.

• Improper flashing 

The Problem: There are three areas where errors can occur with flashing: improper cuts, improper overlaps and missing flashing.

The Fix: Flashing should be installed in the required “weatherboard” fashion (upper layers overlapping lower layers). 

• Improper or insufficient sealant

The Problem: Too often, little or no sealant is applied behind the nail fin or flush flange. Or, there is not enough sealant to accommodate thermal movement or building settling.

The Fix: The bead of sealant should be sufficient to fill the gaps, at least 3/8 of an inch to ¼ of an inch, and have enough movement capability to match the building.

• Using flush fins as nailing flanges

The Problem: Flush fins are not designed to be structural elements, but simply a means to assist in flashing the window to the WRB. (And yes, this really happens.) 

The Fix: Flush fin windows are generally mounted by fastening through the framing into the rough opening.

In short, water penetration-related installation errors can be prevented by heeding one simple admonishment: always think of where the water is going to go and avoid directing water into the building. 

Compromised operation

Window openings must be properly measured, and need to be plumb, level and square, allowing a window to maintain its shape and operate properly. Typical items to watch for include the following. 

• Not checking the rough opening

Even though there is a lot of schedule pressure from other trades, if the rough opening is not checked, the installer will often try to squeeze a window into too small an opening or use too many shims in an oversize opening.

• Not enough fasteners or improper fastener location

I received an inquiry about whether it was sufficient for an installer to use four fasteners, one at each corner. Also, toenailing (driving the nails in at an angle) is a common error. Toenailing can impart stress to the window where the jamb will pull away from the sash, creating gaps the first time the sash is removed. 

• Uneven installation

All gaps between the sash and frame should be uniform and not bowed in any way. A final check and adjustment of the window should be done before the brick or drywall is installed. Attempting to fix it after all other work has been completed can be very expensive. Unfortunately, some installers make little effort to adjust a window at all.

• Uneven shimming

A window that is shimmed only in the center can cause the sill to bow. The window should be shimmed underneath the mainframe jambs.

• Use of improper expandable foam

Using foams that are not specifically designed for window installation can put pressure on the window frame and cause deformation, making the sash difficult to operate. Use only low-pressure foams specifically formulated to fill the cavity between the window and the rough opening.

• Improper handling of jambliners

Improper handling of jambliners—particularly “compression-style” jambliners—can compromise the operation of a tilt-in sash that is designed for easy cleaning. 

Many manufacturers spend significant amounts of time developing installation instructions. Always follow the manufacturer’s installation instructions; failing to do so may void warranties that are offered. If the manufacturer doesn’t offer instructions, AAMA InstallationMasters can be used as a guide. The InstallationMasters program offers training and credentials to window and door installers. The training covers the full range of the installation project, from initial site inspection to final cleaning and maintenance of installed product. 

Rich Rinka serves as technical manager, standards and industry affairs for the American Architectural Manufacturers Association. Rinka previously worked in the industry as a field technical engineer for a component supplier and developed and holds four patents related to sealants.