Weatherproofing

The majority of older storefronts have plate glass display windows.that are clear, single sheets of glass at least ¼ inch thick with a smooth, polished surface on both sides. Your first instinct might be to replace the window while remodeling the space.  However, you might want to reconsider this decision for two reasons: First, plate glass is no longer manufactured, and its modern equivalent (“float glass") cannot match plate glass in smoothness and lack of distortion. In addition, this type of glass is not polished.

Second, while the resistance to heat flow is doubled with the use of insulated glass, this increase is minor when compared to the value of insulating walls and attics.  For example, the “R” value (the standard unit of measurement for a material’s resistance to heat flow) only increases from 1 to 2 for insulated glass.  However, the “R” value is measured between 16-20 for insulated wood frame walls and can be as high as 32 for attics that have 12 inches of insulation.

You have several options to help control heat loss and gain in your space such as:

• Weatherstripping and Insulation: If the plate glass is intact, it might make more sense to weatherstrip around its perimeter to cut down on drafts, rather than to replace it with insulated glass. Designing the heating system so that forced air vents are near the windows will also increase the level of comfort.  
  
  Interior storm windows could be installed directly behind the storefront window and could be removed during the summer.  Unfortunately, the framework necessary to support the storm windows would probably be permanent and interfere with the appearance of the undivided display windows. 
  
  A much less expensive and seasonal option is to install plastic sheeting during the winter months. Not only is it widely available at area hardware and home improvement stores, but using disposable, self-adhesive kits can make the activity easier. 
  
  If the original display glass is already broken, replacing it with insulated glass makes sense.  This will cut down on noise transmission as well as reduce condensation.  If, however, the window is larger the nine square feet you will have to replace it with safety glass.  See the previous section, Security, for additional information on safety glass. 
  
  
• Insulated, Glass-like Panels: As protection against excessive heat loss (or gain), an insulated panel system might also work. Generally three inches thick, these pre-fabricated modular panels are similar in appearance to sand blasted glass, and are translucent. Used in combination with clear glass,  they may be appropriate in projects where original materials are missing and privacy or energy efficiency is a key concern. 

• Passive Solar Heating: South or southwest-facing storefronts can take advantage of their large expanses of glass for passive solar heating in the wintertime. In a passive system, heat gain from the windows is stored during the day, and released to the interior rooms at night. The heat is stored either in an enclosed space behind the storefront glass, or in thick masonry walls or other heat collectors behind the glass. These systems can be installed with minimal effect on the exterior appearance of the storefront. Some, such as water-filled tanks, can be custom-designed to be decorative and energy-efficient.