How to Replace Exterior Storm Windows

Storm windows add to the insulation value of the existing windows.

Storm windows add to the insulation value of the existing windows.

Like anything left out in the weather, storm windows eventually deteriorate, and when they begin to rot, or you can no longer see through the glass, it's time to replace them. The job isn't difficult, as long as you don't mind working on a ladder; and the most important part of it is measuring for the new ones. Once you have ones that fit, you should be able to install them with a screwdriver.

Types of Windows

If you have an older house, your windows are probably made of wood, and the window casings have a stop inset just deep enough to allow the frame of a storm window to sit flush with the outside of the casing. These types of windows often have rotating clips to hold them in place. Aluminum windows, on the other hand, can have one of two types of casings. The so-called "Western" casing is similar to a wood casing, while an "Eastern" casing has no stops. On this type of casing, the window overlaps the casing and gets attached to it.


You need several measurements to make sure that your new storm window will fit. You should measure horizontally at the top, middle and bottom of the casing and vertically along both sides and the middle. If it's a wooden or Western casing, the smallest horizontal and vertical measurements are the ones you should use, and the new window should be 1/4-inch smaller than those measurements. You need the largest measurements if it's an Eastern casing, however, and the window dimensions should be 1 1/4 inches larger than them. The measurements are more accurate if you make them after removing the old storm window.

Removing the Old Window

You may have to replace the storm windows while standing on a ladder, so make sure that it's tall enough, and that you tie it off and that you keep the area underneath it clear while you're working. After unscrewing the old window or rotating the clips to release it, you may have to pry it out if it's painted. Start at one corner and work your way along the bottom with a flathead screwdriver or pry bar. As soon as you can get a grip, angle the bottom toward you and support the window with both hands while you lower it.

Fitting in the New Window

If the old window was rotting, carefully inspect the sill, because you may also have to replace it. If so, the reason is probably that it has no weep holes to allow condensation to drain. If your sill hasn't rotted yet, but doesn't have these weep holes, drill them through the bottom with a 1/4-inch drill bit. After that, you can lift the new window into position. Because you measured carefully, it will fit into place without any forcing so that you can drive the screws or rotate the clips to hold it.

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