Why Windows Fail

Homeowners typically consider replacing windows because they are unsatisfied with their current windows. Understanding why windows fail is essential to choosing the best window and installation type to meet expectations. It can be the difference between being “satisfied” or “absolutely ecstatic” with a window project.

Air Infiltration

Many older window designs have no weather stripping as we know it today. The air-seal was achieved through wood against wood contact or wood against metal contact. Neither would be acceptable by current standards. Today, all windows are tested and receive an air infiltration rating (CFM rate). No operating window has achieved a zero CFM rating. For a homeowner in a climate that experiences subzero temperatures and strong wind, an expectation that NO cold air be detected coming through a window is unrealistic. Contemporary designs use multiple weather strips at each contact point. Double weather strip systems are commonplace today, although some windows still rely on a single seal. The tightest windows today for air infiltration incorporate triple weather strip designs that put three pieces of weatherstripping at each point of contact. Homeowners in colder climates should strongly consider triple weather strip windows and the lowest CFM ratings.

Newer windows with serious air infiltration problems can sometimes be traced to a manufacturing issue, however subpar installation is more commonly the culprit. If daylight can be seen through the weather stripping, a physical adjustment to the window is in order. Often times this adjustment can be very simple once the cause of the gapping is diagnosed. When the air infiltration is coming around the window rather than through the window it is a sign of insufficient insulation and/or sealing of the window. This can be caused by something as simple as an installer forgetting or missing insulation on a window, or just one side of a window (it happens to even the best). Once diagnosed, this is an easy fix.

A common air infiltration issue with a pocket window install can be cold air leaking around the old frame. A new replacement window may be well insulated to the old frame, however if insulation is lacking around the old frame, a cold drafty window opening will still exist. This issue is age related and can be a compelling reason to opt for a full frame install with some older homes.( see: Types of Install).

A more complex issue can be cold air circulating in the wall and finding an entry point to the interior around a window opening where the drywall or plaster meets the studs. This point is well to the inside of where the window is installed and insulated, and not an area typically addressed during a window install. However, once new windows are installed it is a problem that is likely to be blamed on the new windows. One sign of this condition in a home is air infiltration around other wall fixtures, such as electrical outlets on exterior walls. This complication is age-related as well, with older homes being at issue.


Insulated glass units with multiple panes can be prone to seal failure. This occurs when the seal keeping outside air from getting between the glass is broken. The “new” air circulating between the glass carries moisture that condenses between the panes. An insulated glass unit with a broken seal can be identified by visual moisture between the glass, or a milky white appearance to the glass. The fix is replacement of the insulated glass unit. Manufacturers Warranties for seal failure vary, but have generally improved with the introduction of more reliable spacer and edge systems for insulated glass. What was once mostly an industry-wide 3-5 year standard for seal failure, is now lifetime with some manufacturers.

It is material to mention stress cracks in any discussion of glass. True stress cracks (cracks not associated with any impact) generally appear in the first year or two, and are more common in colder climates. For window companies, stress cracks are often a mystery. They may be almost nonexistent for years, then rear their ugly heads for no apparent reason, only to disappear again for years. Although most manufacturers will cover their products for a period of time regarding stress cracks, it may pay to read the fine print.


Condensation is water vapor in the air being drawn to the coolest surface in a room, usually a window. The amount of condensation that is acceptable in a home is highly subjective. Fortunately, it is also easily controllable. For Homeowners in a colder climate that prefer a higher humidity level, the expectation of NO condensation is unrealistic. To learn more about condensation, acceptable humidity levels in relation to temperature, and steps to reducing condensation…see Window Condensation Facts and Tips.

Frame Degradation (Rot)

Some frame degradation can be expected from wood windows in older homes. It is notable how well some wood windows have held up in some 80, 90, and even 100-year-old homes. The failure of wood windows in homes less than 20 years old is equally notable. Frame rot is the issue and it makes the old saying: “They sure don’t make ’em like they used to” ring truer than ever. A twenty year old or less window with frame rot, barring excessive humidity problems, has serious design and/or material deficiencies.


Insect infestation can be hazardous to a home, particularly in warmer regions. When unwanted moisture is introduced behind a window frame, insects are almost a guarantee in some areas. Full frame window replacements offer a unique opportunity to inspect the rough opening and treat for infestation before the new window is installed (see types of install).