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Measuring Window Frames for Storm Sash
Determining Sash Opening Width and Height

For Eastern style windows having blind stops:

 

When measuring sash openings to determine the size of the storm sash, measure the distance between the outside casings to determine the sash opening width. For accurately fitting storm sash, always take this width measurement at three different elevations on each window, i.e., the bottom, center, and top of the frame. Record the LARGEST width on the form.

Similarly, measure the height of the sash opening at both the left side and the right side of the frame. Record the LARGER of the two measurements on the form. IMPORTANT: always take the sash opening height at the outside of the casing, never at the back of the casing or outside of the blind stop. The height is greater at the outside of the casing due to the slope of the window sill, and a height measurement at the blind stop will result in a storm sash that is too short.

If the window frame appears to be significantly out of square, it is important to measure the “out-of-squareness” because the storm sash must be made with extra-width top and bottom rails to compensate for this condition. The best way to measure for squareness is to carefully measure the two diagonals, or in other words, from one corner of the sash opening to the diagonally opposite corner. If the window is in square, the two measurements will be the same. For windows that appear to be square, this step is not necessary.

Finally, measure the slope of the window sill below where the sash is to be hung. Set a protractor on the sill and measure the angle between the sill and any vertical edge. The difference between this angle and 90 degrees is the sill slope

Measuring sill slope with desk protractor.

Record the sill slope on the form.

The glass sizes in the storm sash should normally be the same as the glass sizes in the Double-hung sash. (In case the DH windows are divided-light, the overall glass sizes are used.) For eastern-style windows, the glass sizes are usually even-inch widths x even-inch heights. Victorian 4-light windows usually have odd-inch sash widths and utilize 4-light storm sash. All other double-hung windows normally utilize 2-light storm sash.

Click on images below to view at larger size.


Obtaining Correct Measurements for Width and Height of Storm Sash Opening

Obtaining Correct Measurements for Width and Height of Storm Sash Opening
Window Nomenclature

Window Nomenclature
Measuring Sill Slope With desk Protractor

Measuring Sill Slope With desk Protractor
Modern Sill with 14 degree Slope

Modern Sill with 14 degree Slope