Natural Resources Canada
Symbol of the Government of Canada

Office of Energy Efficiency Links

 

Personal: Residential

Menu

Repairing or Improving
Existing Windows or Doors

Storm Windows

Storm Window

If your windows are in good condition, extra glazing can be added quickly and easily by installing storm windows, either interior or exterior. A number of options are available.

Interior Storm Windows

These are generally attached directly to the window frame. This helps reduce air leakage around the window.

A well-sealed interior storm window reduces the risk of condensation because its surface temperature is close to that of warm room air. Any condensation that does occur is on the storm window, which prolongs the life of the main window.

Interior storm windows are lighter and more accessible than seasonal exterior storm windows. They are therefore particularly useful on upper floors.

One disadvantage of interior storm windows is that blinds or other window treatments may have to be repositioned to accommodate them.

Interior storm windows are typically used in the winter only and are stored for the rest of the year. However, in an air-conditioned house, interior storm windows can also help during the hot summer months, keeping heat out and cool air in.

To minimize condensation and air leakage, interior storm windows should be sealed tightly so that no warm air gets between the storm unit and the original window after installation.

The first two approaches can be inexpensive projects for do-it-yourselfers, while the last two are more costly and may require the services of a contractor.

The most common interior storm window systems are:

Heat-Shrink Film With Double-Sided Tape

This is one of the easiest do-it-yourself options available to homeowners. Most hardware and building supply stores sell the kits and include instructions for installation.

The film is attached to the window trim with two-sided tape. The film is then heated with a hair dryer to shrink it tightly across the window. In most cases, the film can be used only once. Although this system provides an excellent seal and good visibility, the two-sided tape can lift paint when it is removed. Once this system is installed, the window cannot be accessed unless the film is removed or punctured.

Here are some points to keep in mind when using heat-shrink film:

  • Lightweight film systems may be damaged if you have young children or pets in the house.
  • Plastic systems must be kept away from strong heat sources.
  • Some people may be sensitive to plastic materials, which can emit odours (particularly when their surfaces are warmed by sunlight).

Plastic supply stores carry a special cleaner that can be used to clean lightweight film and reduce static.

Applied Window Films

Originally only used on cars to tint the windows, these films are now being widely used on residential and commercial windows where heat gain or glare is a problem. Some films are now even treated with a low-e coating to reduce heat loss, but they are not as effective as windows with insulating glass units that have low-e glass and a gas fill. Caution is advised because the application of a window film may cause glass breakage and also void any warranty offered by the window manufacturer.

Clear Rigid Acrylic Sheets With Snap-On or Magnetic Seals

Clear Rigid Acrylic Sheets With Snap-On or Magnetic Seals

These systems are more durable than the previous two options. The snap-on system works like the spline-and-channel system, but it is more substantial because it holds a heavy acrylic sheet in place. The rigid glazing is easier to attach and remove than film, is easier to clean, is more durable and has a more finished appearance.

To install a magnetic seal system, use double-sided tape to fasten a metal strip to the window trim. The strip can be painted to match the frame. Then secure a magnetic moulding to the acrylic sheet, and press the sheet into place on the metal strip.

When the acrylic sheets are not in use, they must be stored in a flat or vertical position (not slanted) and in a cool place that is protected from exposure to sunlight and excessive heat. Many plastic supply stores sell these systems and can cut the sheets to the size required. As well, some firms specialize in manufacturing and installing these systems (check your local Yellow Pages).

The magnetic seal is a popular option for heritage homes and highrise condominiums, since it is possible to make the attachment system virtually indistinguishable from the main window. However, thermal contraction and expansion and the weight of the acrylic sheet can cause the magnetic strip to release accidentally. As a precaution, a few well-placed turn buttons can be used to supplement the magnetic seal and hold the unit firmly in place.

Specialty Products

Another option worth considering is a multi-layered, laminated polyester film that is black on one side and silver on the other. The film has a perforated appearance (like a microwave oven window) but does not allow air to pass through it. The system is attached to the window trim by means of a Velcro fastening system. In winter, the silver surface faces in, reflecting heat back into the house. The fastening system allows the film to be easily reversed in summer, with the silver side reflecting solar energy back out through the main window. This product is effective at reducing unwanted air leakage in both summer and winter, but it tends to block daylight, darken the room and reduce visibility. It may be most suitable for areas that have high solar heat gain and heat loss, such as sunrooms.

Sashless Sliders: A Special Case

Sliding windows that are panes of glass not encased in a frame are highly inefficient. At the very least, they should be supplemented with interior storm windows. A better solution is to have a contractor retrofit the windows by installing the existing glazing in new sashes that incorporate weatherstripping. The sashed units are then reinstalled in the original frames.

Exterior Storm Windows

Exterior storm windows are usually constructed of a wood or metal frame, with glass or an acrylic sheet as glazing.

Exterior storm windows can be either seasonal (installed in the fall and removed in the spring) or permanent. Seasonal storm windows should be inspected each year before installation to ensure that the glazing, putty and weatherstripping are in good condition. A drawback of seasonal units is the labour involved in installing and removing them each year, as well as the need for storage.

Permanent exterior storm windows are usually equipped with a built-in screen and a sliding sash. When using exterior storm windows, the main interior window must be air sealed more tightly than the storm window to prevent moist household air from entering the space between the windows and being trapped, where it can condense and cause deterioration of the sash and frame.