Insulating Glass: Flexing and its Effect on GBG
There are numerous environmental conditions and changes that may cause insulating glass to flex. This flexing is a natural response to these environmental conditions and may reduce the distance between the two pieces of glass in the insulating glass (IG) unit. When internal grilles are used (grilles between the glass, or GBG) there is the potential that GBG may contact the airspace glass surfaces (surfaces 2 and 3) of the insulated glass unit. This contact could cause a brief rattling noise. This is not a product defect and does not warrant glass replacement. Environmental changes and conditions that effect insulating glass. Temperature and Barometric Changes On a daily basis, the outdoor temperature can typically change 20 degrees F from high to low. In some locations of the country the seasonal swing from summertime high to winter low can be 100 degrees F. An insulating glass unit is exposed to all this exterior change while facing a relatively constant interior room temperature. When the IG airspace temperature is below the temperature at which it was sealed, the glass panes may flex inward. Conversely, hot temperatures may flex the glass outward. Just like temperature, barometric pressure changes can cause IG glass to flex. During low pressure conditions, the glass flexes outward- during high pressure conditions the glass flexes inward. Elevation With an IG unit, every 1000ft of altitude increase has the same flexing effect as a 10 degree F temperature increase in the airspace. The principle difference when comparing altitude changes to temperature changes is that altitude deflection is constant. Conversely, it is possible for an inward flex to occur if a unit is installed at a lower altitude than where it was fabricated. Wind Loads Outdoor pressure from wind loads on glass can create minor glass flexing. Internal pressurization of buildings from HVAC systems can create similar effects. Similar to glass flexing from barometric changes, this is the natural reaction of glass to such outside forces. IG Unit Glass Type and Size The flexibility of glass is also different for various combinations of size and glass thicknesses. Changes in the air space gap width will also change the total deflection response. Both of these effect glass surface curvature and the potential for GBG rattling. Swinging or Sliding Patio Doors that are rapidly swung open or shut and large glass units utilizing long spans of GBG are particularly susceptible. Temperature, elevation, wind loads, and IG unit glass type and size are all factors that contribute to insulating glass flexing and possible grill contact. A combination of these factors increases the potential for this condition to exist. The rattling sound that may occur as a result of glass flexing, resulting in GBG contact, does not compromise the quality of the door or window unit. In some applications, it may be advisable to consider an alternative divided lite option. Excerpted from Marvin Windows and Doors Customer Service Bulletin