How Much Room Should Be Left in Storm Windows for Glass Expansion?

Storm Windows

• Storm windows help add extra layers to ordinary house windows. Traditionally, storm windows have additional panes of glass to protect against storm damage; however, the term "storm window" has expanded to include coverings that protect the inside of the home from UV damage and help prevent leaks where air can escape and heat can pass more easily between the inside and outside. There are two primary types of storm windows: glazed versions and window films.

Window Films and Space Openings

• Window films are the lighter, easier to install version of storm windows. These are UV filters that can be sealed against existing windows to improve thermal barriers while also blocking some UV light from getting through. If you try to install these films against the very edges of your glass window, they will peel and crack when the glass changes shape. Leave about 1/16-inch between the edge of the window and the film when you install it these coverings.

Glazed Storm Windows

• Glazed storm windows have panes of glass installed against existing windows to double the panes. These layers of glass should not be installed directly against each other since this prevents them from bonding properly. The space between the two panes will differ based on the frame and type of window, but it is generally a fraction of an inch.

Weep Holes

• Installing glazed storm windows poses the possibility of water damage, especially with those types designed for seasonal removal. If water gets trapped between the existing window and the storm window, it can cause rot and moisture issues. To prevent this trapped moisture, always install weep holes when mounting the windows. Weep holes should be 1/4-inch in diameter and never be caulked over. The pair of holes should be installed several inches from either side of the window, directly into the storm window frame.