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Interior Storm Window Systems
Interior storm window systems have gained in popularity in recent years. They offer the following advantages:
- They are generally attached directly to the window frame, which helps reduce air leakage around the window, and can be attached in four convenient ways, as discussed below.
- If an interior storm window is well sealed, it reduces the risk of condensation because its surface is closer to warm room air. Any condensation that does occur is on the storm window, which prolongs the life of the main window.
- They are lighter and more accessible than seasonal exterior storm windows and are therefore particularly useful
on upper floors.
Figure 7. Compression and sweep weatherstripping on a casement window
One disadvantage of interior storm windows is that blinds or other window treatments may have to be repositioned to accommodate the storm window.
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 keep heat out and cool air in during the hot summer months.
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Sashless Sliders - A Special Case |
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Sliding windows that are panes of glass not encased in a frame are inefficient and, at the very least, 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. |
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 four most common interior storm window systems are discussed below. The first two approaches involve inexpensive, do-it-yourself products, while the last two are more costly and may require the services of a contractor.
Heat-Shrink Film with Double-Sided Tape
This is one of the easiest do-it-yourself options available to homeowners. Kits are sold at most hardware and building supply stores and include instructions for installation.
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Points to Keep in Mind |
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Lightweight film systems may be damaged if you have young children or pets in the house.
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Plastic systems must be kept away from strong heat sources.
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Some people may be sensitive to plastic materials, which can emit odours (particularly when their surfaces are warmed by sunlight).
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Plastic supply stores carry a special cleaner that can be used to clean lightweight film and reduce static. |
With this system, two-sided tape is used to attach the film to the window trim, after which the film is 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. As well, once this system is installed, the window cannot be accessed without removing or puncturing the film.
Clear Plastic Film with Spline and Channel
A rigid plastic channel is permanently attached to the window frame using small nails, screws or double-sided tape (as shown in Figure 8, a lower crosspiece is added to the sill to create a flush fastening surface). A clear plastic film is then stretched tightly across the window and snapped into place using the spline section (see Figure 8). The plastic film is reusable for several years and is airtight. One disadvantage is that the film may not be as clear as heat-shrink film. The spline-and-channel system should last for several years.
This system is usually sold in kits (available in a variety of colours), but the individual components can also be bought separately. Follow the manufacturer's instructions carefully when installing the spline and channel, and be sure to use the recommended thickness of film. When not installed on the window, the plastic film should be stored hanging over a rod to avoid creasing.
Figure 8. Clear plastic film with spline and channel.
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, except that it is more substantial because it holds a heavy acrylic sheet in place (Figure 9). The rigid glazing is easier to attach and remove than film, and it is easier to clean, is more durable and has a more finished appearance.
To install a magnetic seal system, a metal strip is fastened to the window trim using double-sided tape (this strip can be painted to match the frame). A magnetic moulding is then secured to the acrylic sheet, and the sheet is pressed 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.
Figure 9. Snap-on interior storm window system applied to window trim
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 PagesTM).
The magnetic seal (Figure 10) 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
There are two products that are most suitable for areas that have high solar gains that make the room uncomfortable: applied window films and multi-layered polyester films.
Applied window films are usually made from a clear or tinted polyester substrate upon which a scratch-resistant coating is placed on one side and an adhesive with a protective liner is put on the other. The film is permanently attached to the window by removing the liner and pressing it firmly on the glass. Window films with a solar-control coating reduce solar gain; help protect carpeting, draperies, furniture and wood from fading; and can even reduce heat loss in the winter. However, there is a small risk of glass breakage due to increased thermal stress, and the use of these films may void the warranty issued by the original window manufacturer.
Multi-layered polyester films are black on one side and silver on the other.
Figure 10. Magnetic interior storm window system applied to window sash
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This article is from Natural Resources Canada web-site
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