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Windows of Opportunity: DIY Window Replacement

Windows & Doors June 28, 2003 Sonia



Replacing old single-pane glass windows with new double-insulated windows can provide one of the greatest energy savings for your home. Modern windows feature two or three panes of glass with an insulating air space between. The higher-quality windows also have an inert gas such as argon between the glass panes, offering an even greater insulating factor. Many modern windows go one step further and have a special coating called “low-E” applied to the glass. This coating contains metallic particles that slow heat loss in the winter and reduce heat gain in the summer. When purchasing windows, look for the National Fenestration Rating Council (NFRC) energy-efficiency label on the windows.

Windows are available in several different styles including single-hung, double-hung, gliding/horizontal, awning, hopper, casement, jalousie, fixed, bay or bow and garden. Most building warehouses carry standard-size, double-hung windows – the most common style. Most warehouses also carry a limited number of specialty windows such as circular, arch and bay or bow. Many other types of windows will have to be specially ordered. Unusual sizes of any window are special-order items. If at all possible, it’s best to replace existing windows with those of a similar size.

Windows are available made of vinyl, metal, wood and wood with vinyl- or metal-clad exteriors. Wood is more energy-efficient than either vinyl or metal. Cladding the outside of the wood window, however, eliminates the need to paint at the time of installation and requires less maintenance in the future. The clad wood windows are higher priced than any of the single-material windows.

Windows are available in two types: new-construction and replacement. New-construction windows are installed from the outside, with no interior or exterior trim in place at the time of the installation. Siding and window trim are installed after the windows are in place. Replacement (sash-only) windows are installed in the existing window frames, leaving both interior and exterior trim in place. The full-frame method is best if interior and exterior window trim is being replaced. Most single-pane windows also require outside storm windows. Storm windows are not necessary with the installation of double-insulated panes, and leaving the storm windows in place takes away from the beauty of the new windows.


Typical old-style windows require lots of maintenance and have lots of air infiltration. First step is to measure the existing windows or determine measurements of the replacement windows.


Measuring for Windows

Proper measurement is extremely important. After determining the brand name and type of replacement windows desired, use the manufacturer’s measuring instructions for their particular windows. Shown is a diagram of an old-style, standard, double-hung window with counterweights or a sash weight system. In most instances it’s best to remove the old interior trim to ensure correct measurements. If you can’t get windows the exact same size, it’s easiest to install slightly smaller replacement windows, reframing the opening as needed. Installing larger windows requires cutting the existing framing – this can, however, result in larger, brighter windows. If making a window taller or wider, it may be necessary to make important structural changes to the existing wall. In many cases the wall will be load-bearing (supporting the roof or another floor above it). Plans to change the structure of these walls should be approved by a knowledgeable carpenter or engineer. You may also be required to have a city or county inspector approve the change. If you have old, pocket-weight style windows, you can easily enlarge the windows by using the pocket spaces on either or both sides of the existing windows. Normally this will require minimal structural changes.

In some instances more than one window may be installed in an opening. The three windows replaced in this article are typical of older homes with the windows requiring sash weights on both sides of each window. Modern windows, such as the Pella window units installed, can be mulled or joined together to fill almost any opening you can imagine. Windows can be mulled together side by side or top to bottom, and can be any combination of operable and fixed windows. Most manufacturers offer some factory-mulled windows, or you can purchase mull kits to join the windows to suit your needs.