The glass industry has developed consensus standards/specifications that address quality aspects of various types of glass used in windows, doors and skylights. These standards are very comprehensive and typically written for manufacturers who have expertise in applying them. The standards are also very specific to a given glass type. These types include raw flat (annealed) glass, heat-treated glass (ex. tempered), coated glass (ex. low-E), laminated glass and IGUs. Unfortunately, the methods of inspection and the blemish or issue criteria are not always the same for each type of glass.

In most cases, a homeowner will have a window, door or skylight that contains an IGU that is comprised of two or more panes of flat glass. Typically, this glass will also have some type of low-E coating. If there is a safety concern or a code requirement for safety glazing, the window may also contain tempered or laminated glass. With a combination of all these glass types in one window, door or skylight, sorting out the appropriate criteria to the respective standard is at best a complicated, if not confusing, endeavor. How then is a homeowner to know whether an issue or blemish is a legitimate concern?

The following is a general guideline offered to simplify the inspection of glass issues for the homeowner. This is not necessarily a definitive guide covering all glass related concerns; that’s the job of the industry standards. Rather, this guideline is a check for a homeowner to flag whether an issue merits consideration for replacement.

Home Inspection Directions

1. Thoroughly clean the glass on both sides with glass cleaner.
2. Stand 10 feet away, directly in front of the glass (90° to the surface).
3. The glass should be illuminated with daylight, but not direct sun.
4. If an issue or blemish is readily apparent, measure the size of the blemish.
5. Contact the manufacturer if the blemish is noticeable and is outside the following limits.

Blemishes



Other Issues