I want to install some exterior storm windows, but the prices are over my budget. I have more time than money now, so I could make them myself. Do you have any building tips and should I use double panes?—Jack W.
With free time and medium do-it-yourself skills, you should be able to build simple storm windows at a fraction of the cost of professionally installed ones. They can be as energy efficient as custom ones, if not more so, because a simple storm panel has fewer joints for outdoor air to leak into your home.
First, make sure your primary windows are in reasonably good condition.
Double-pane storm windows are somewhat more efficient than single-pane, but I would not recommend them for most homes. They are more difficult to build and the material costs will be almost twice as much. The payback from the extra energy savings with double panes would be greatest in cold climates, but there you would likely have a problem with fogging between the panes.
The energy-efficiency improvements with storm windows come primarily from the dead-air space created and from blocking the direct force of the wind on your primary windows. The storm windows should be mounted as close to the primary window as possible. You might think a wider dead space would provide more insulation, but energy-robbing internal air currents can develop between the storm panes and the primary windows.
Use 1×2-inch lumber to make the rectangular framing for the storm windows. Any type of wood will work. Redwood or cedar is rot-resistant and can be stained and finished with clear urethane. Pressure-treated lumber holds up well, especially in wet areas, but it does not accept paint as well as standard lumber.
Use a miter box to make accurate 45-degree angles. This makes a more professional-looking and stronger frame corner joint than just a butt joint. Size the outside dimension of the frame to be slightly smaller than the outdoor window opening to allow room for foam weatherstripping around it. The compression of the foam should hold the storm window in place, but mechanical fasteners are better for windy areas.
Use clear acrylic plastic (Plexiglas) for the glazing. Since the energy efficiency comes from the dead-air space, not the plastic or glass itself, any thickness will work fine.
If you have children who play near the windows and you want a tougher plastic for first-floor windows, use more expensive polycarbonate (bulletproof glass). Polycarbonate may yellow a little over time if it is exposed to continuous direct sunshine.
If you have a router, make a slot along the inner edge of the frame sides before you assemble the frame. This slot will hold the acrylic sheet. The acrylic sheet will have to be cut slightly larger than the inside of the frame so it is secure in the slot. If you do not have a router, nail some narrow wood stops on each side of the edge to form a slot.
A still easier method is to use a bead of clear silicone caulk to hold the acrylic pane in the frame. Use a staple gun to staple the frame corners together. Also use a strong glue in the frame corner joints. Some of these glues expand as they cure, so use it sparingly.
Place the storm window in the window opening and measure the clearance gap around it. Buy adhesive-backed foam weatherstripping, which is slightly thicker than the gap. Peel off the backing and stick the foam to the frame. Leave two small 1/4-inch gaps in the foam at the bottom to function as moisture weep holes. Force the frame into the window opening so the foam is compressed.
Mail requests and questions to James Dulley, Kentucky Living, 6906 Royalgreen Drive, Cincinnati, OH 45244. Go to www.dulley.com to instantly download.