How to Measure for Storm Windows

Write down all window opening measurements as they're made.

Installing storm windows on your home's exterior can keep less-than-efficient existing windows from making your home drafty and leaking costly interior heat out into the air. Where outright replacement of leaky windows can be prohibitively expensive, installing storm windows is a much cheaper and easier process. Ensuring a proper storm window fit means taking multiple measurements from many different angles. A few additional measurements made need to be taken if the window opening you're measuring has warped with age.

Things You'll Need

• Tape measure
• Pen or pencil
• Paper

Instructions

1. Assess whether the window to which you'll mount the storm window has a "Western" casing or an "Eastern" casing. Windows with a "Western" casing will require the storm window to be secured to a recessed stop within the window opening. Windows with an "Eastern" casing have no recessed stop, and require the storm window to partly extend over the casing and attach to it.

2. Measure the width of the top of the existing window. This measurement, and all of the measurements that follow, should be within 1/16 of an inch. Write down all measurements for future reference.

3. Measure the bottom of the existing window where the window frame meets the sill.

4. Measure the left and right sides of the existing window, as well as the center of the window from top to bottom. For older homes, measuring the center of the window can determine whether any bowing or warping has taken place that would throw off the other existing window measurements.

5. Measure the existing window diagonally, once from the bottom left corner to the top right corner, and again from the bottom right corner to the top left corner.

6. Choose a storm window that is at least 1 1/4 inch wider than the width of the window opening, and 1/2 to 5/8 of an inch taller than the window opening, for a window with an "Eastern" casing. Choose a storm window that is 1/8 to 1/4 inch narrower and shorter than the window opening for a window with a "Western" casing.

Tips & Warnings

• Don't caulk the bottom of your storm window when it comes time to install. Leaving the bottom uncaulked allows for any trapped water between the storm window and existing window to escape.

References

• City Glass & Upholstery: Tips for Measuring Existing Windows for Storm Windows
• This Old House: Weathering the Storm