Help: My Vinyl Clad Windows Have Mildew in the Middle

Problems

• When you opt for vinyl clad windows, you’re limited to light colors, as heat builds up in dark colors, causing expansion in the materials. Vinyl clad windows can also crack in cold weather. These issues can potentially lead to or exacerbate a problem with moisture buildup. If the cladding on your windows fails, the wood beneath the vinyl may become exposed to the elements, allowing mildew to form on the wood surfaces and increasing the potential for wood rot.

Multi-Pane Windows

• Double-pane and triple-pane vinyl clad windows use air space between the pieces of glass to provide additional insulation. The spaces between the glass may be filled with denser-than-air krypton or argon gases. If the corners of these windows are attached using welds rather than screws, the weather-stripping groove may become gapped or distorted, warns the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy.

Material Failures

• Window frames are rated on an A/B/C scale based on how well they age when exposed to UV light, temperature extremes and moisture. Windows with less than an “A” rating are more prone to problems as they age. Fogged glass may result when the perimeter seal fails on double-glazed windows, notes the This Old House website, which warns that reduced energy efficiency, poor visibility and the buildup of condensation between the glass panes can occur due to seal failure.

Solution/Prevention

• To prevent issues with gaps due to welds, the Department of Energy suggests inspecting windows with welds to visually verify that the weather stripping meets at the corners with no openings or breaks in the continuity. To fix fogged glass, add a new sash or replace the entire window, suggests the This Old House website, which recommends windows with a removable grille muntin over grille-in-glass versions because the former allows the grid to be removed for cleaning if issues such as mildew arise, while grille-in-glass muntins are permanent and make the windows less energy efficient.

Cleaning

• Mildew may form between the panes of double- or triple-pane windows when their airtight seals are compromised and moisture can enter the space. This is not an issue a homeowner can repair. Consult the company that manufactured or installed the windows regarding the possibility of professional cleaning and repair, or replace the windows. To clean mildew on outer surfaces of your windows, wash the affected areas with dish soap and water, then with a solution of 1 cup of chlorine bleach to 1 gallon of water.