Restoration Guide: Glazing Windows and Doors

Barbara Marquand

Editor's Note: This is article 3 of 12 in Chapter 4: The Windows and Doors Guide of Old House Web Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development Rehab Guide.

Section 1--Overview

Glazing--the glass part of the window--not only provides you with clear views of the outdoors, but, thanks to new insulating technologies, helps keep the warm air inside on cold winter days and reject the outdoor heat on torrid summer afternoons.

If your old house still has single-glazed windows, then you're losing money every year in the form of high energy costs. Today's windows feature two or even three layers of glazing. The spaces between the glass layers are filled with air or inert gasses, such as argon or krypton, to reduce heat, cold, and noise transmission. In addition, new glazing coatings and films have been developed to improve window performance. These coatings reflect heat and ultra-violet rays, but allow for the maximum amount of visible light to shine through for optimum views.

Insulated windows cut heating, cooling, and lighting bills, increase the comfort of the home by reducing condensation and drafts, and prevent damage to furnishings from harmful rays. This section of the Windows & Doors volume of The Old House Web Restoration Guide covers the basic types of glazing coatings and films and how to restore glazing.

Section 1--Low-Emissivity Coatings

A variety of low-emissivity--low-e--coatings are available. All of them improve the insulating quality, but they vary in how much heat from the sun they reject. Your choice of coating depends on where you live and the orientation of the house. Low-e coatings are usually placed on the interior surface of glazing and are typically closest to the source of heat to be reflected. Some windows use multiple coatings and intermediary plastic films for maximum performance.

Here's a look at the basic types of Low-e coatings:

  • High-transmission coatings allow the most solar heat to enter the house and minimize heat loss in the winter--best for cold climates.
  • Selective low-e coatings allow the greatest amount of daylight and moderate heat transmission, reducing winter heat loss and summer heat gain--best for climates where heating and cooling are necessary.
  • Low transmission coatings reduce glare and let the least amount of heat enter the house. Think Las Vegas or Miami.

Check the National Fenestration Ratings Council (NFRC) rating to judge the performance of each coating, and keep in mind you can use different low-e coatings for different sides of your old house.

Energy efficiency isn't the only consideration for glazing. You should also think about impact, wind and fire resistance. Check local codes for minimum requirements in your area. For historic preservation, specialty glazing products for matching existing windows are available.

Glass block began enjoying a revival a decade ago, and many homeowners are attracted to its ability to block noise, diffuse light and provide security. The new generation of glass block features a mortar-less application with improved fire ratings and is available as a lighter-weight acrylic product.

Section 2--The Tools, Materials and Know-How You Need

2.1: Cleaning Up Damaged Glazing

Before you repair glazing, determine what caused the damage. Caustic chemicals, such as runoff from masonry materials, or scratching from sand or branches can hurt glazing. If the damage is minor, you might be able to restore glazing with a simple ammonia-based cleaning solution, or xylene, toluene, or trisodium phosphate. You can also repair damaged glass with a mechanical polishing method, but hire an expert unless you really know what you're doing. Also, make sure other components, such as sealants, are OK. If those are damaged, then you might want to think about replacement.

2.2: Applying Film To Glazing

All sorts of tinted and reflective film products are on the market to control glare and heat and block UV rays. The products are formulated for specific climates, so you can find one that provides the most benefit for your area. Application is relatively easy, and films might eliminate the need for blinds or curtains to control sun exposure. But the gains you'll get from applying film won't equal the performance of factory-applied materials, and the surfaces won't perform as well over the long haul. Applying a film to an insulated window might even upset the expansion and contraction of the glazing, which could put stress on the glass and seal.

2.3: Applying Safety Film

Safety film provides protection against shattering and can be combined with other films for controlling heat and glare. Consider safety glass if you live in a high-wind area or want to guard against vandalism. Bear in mind, though, that all parts of a building must provide equal resistance to prevent storm damage or a break-in. Safety glazing must be secured in the frame itself, or the protection won't extend to the entire window unit. One possible drawback of safety film is a slight obscuring of clear views.

2.4: Patented Insulated Glass Inserts For Preservation

A Massachusetts-based company called Bi-Glass Systems patented a window restoration process that replaces single-pane glass with double-glazed, insulated low-e glass. The process is targeted to homeowners who want to preserve the look of their old windows but improve their performance and energy efficiency. The process works for almost any type of window, from Victorian bent glass to period glass to more contemporary styles. The installation doesn't disturb surrounding materials and the cost might be lower than total replacement. Check the company's Web site to see if a dealer is available in your area.

2.5: Glazing Replacement

Although rarely done, you can apply new glazing to repair old windows. The option might be cost effective if you're trying to address a single factor, such as impact resistance. But replacing the glazing might be compromised by the frame and sash materials, and costs vary widely by region, so evaluate carefully before proceeding.

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