Defective humidification units in a home may lead to higher humidity levels, exacerbating deterioration of window sash.

For the past 30 years, window frames have been constructed with thermal breaks that tend to reduce cold areas that encourage condensation.

Some thermal breaks have been improperly designed, allowing significant cold transfer and increased condensation. These problems occur over time.

2. Sash Deterioration Defect

Older sash was constructed of hard woods with closed cell structures, which minimized the damage from water as compared to modern sash, which utilizes soft woods with an outer, water-resistant cladding. Figure 2 below shows an example of a modern casement window 10 years after installation, well within the warranty period.

Rain water has penetrated the outer aluminum protective cover and has rotted the bottom of the sash. This area is typically unseen by the home owner and becomes noticeable when there is difficulty opening or closing a window. The rotted bottom of the sash near the sill does not retain a square shape, causing jamming of the window while opening.

Figure 3 to the right is a close-up of the deteriorated wood where water became trapped after penetrating the outer cladding. The windows were properly installed and maintained. A design defect exists in that water could easily bypass the seal and accumulate in an area that did not drain or dry out readily.

Researching recalls by the window manufacturer may reveal a recall as was the situation in this case where the manufacturer acknowledged the defect and gave a prorated credit to the homeowner for the failure during the warranty period.

Of course, water can enter a properly designed window system as a result of improper installation, handling damage (shipping) or other external damage (rocks from lawn mowers) suggesting that an inspection of the window system may be necessary.

3. Building Structural Movement

Structural movement of a building can cause problems with window systems. Deflection of the building structure can occur from settling, nearby construction, excessive loading, defective construction, deterioration of the structure, foundation movement and wind. Building deflection in the form of racking causes the window frame to distort, resulting in sash failure, window cracking and jamming when the window sash is raised or swung outward (Refer to Figure 4 below).

The damage can occur suddenly as a result of high wind pressure or excavation close to the building. The damage can also occur gradually as exemplified by settling or structural deterioration.

The window in Figure 5 below suffered from cracking and deformation of the sill.

As evident in Figure 6 below, a rotted support beam (arrow) under the sill that is deflecting downward. Brickwork also attests to the downward deflection of the support beam, a long term deterioration related problem.

As in most losses, it is prudent to inspect the window system and obtain information from the insured as to the particulars of the problem with the window system.

This may include:

• The age of the window.
• When the damage was first noticed.
• Or any coincident circumstance, etc.

Photographs from the underwriters or an aerial (satellite photo) view of the home may show evidence of a preexisting condition.