Large Windows

The Problem

If a building has large windows, the glass may break when the ground shakes, especially if there are only narrow walls on each side of the windows. In a major earthquake, buildings with large storefront windows can lean over and even collapse if the front wall is inadequately braced. Buildings on crowded city blocks are especially prone to damage if the buildings are near enough to pound against each other during earthquakes.

The front window of this Fortuna auto parts store broke in the 1992 Cape Mendocino earthquake.
Source: California Seismic Safety Commission

The windows in this San Francisco building probably broke because its frame flexed too much in the Loma Prieta earthquake of 1989.
Source: California Seismic Safety Commission

How to Identify It

Check to see if there are solid walls, diagonal braces, plywood panels, or heavy steel frames next to any large window. Such a window does not always indicate an earthquake weakness. There are no simple rules of thumb for determining whether or how much bracing is needed or where it should go.

You will need the help of an architect or engineer with experience in earthquake strengthening.

What Can Be Done

New steel framing or plywood paneling can be installed around a storefront window. New window mullions can be added to replace a large piece of plate glass; this change will allow for more movement. Plastic film can be applied to the windows to keep the pieces from scattering if a window does break.

You should consult a qualified architect or engineer if you have large or numerous windows, especially on the ground floor of your building.