Measuring Rough Opening

To ensure a proper fit for a new door, it is crucial to measure the rough opening accurately. The rough opening refers to the space within the stud wall structure before installing the door jamb. Follow these steps to determine the appropriate door width and height:

1. Measure the Width:
   • Measure the rough opening width from the inside of one wall stud to the inside of the opposite wall stud.
   • Take measurements at three points: the top, middle, and bottom of the opening.
   • Use the smallest of these three measurements.
   • Subtract 2 inches from this width to determine the needed door width.
     • Example: If the rough opening width is 38 inches, the required door width is 36 inches (38″ – 2″ = 36″).
       
2. Measure the Height:
   • Measure the rough opening height from the floor to the bottom of the upper stud.
   • Measure the height at both corner edges of the opening.
   • Use the smaller of these two measurements.
   • Subtract 3 inches from this height to determine the needed door height.
     • Example: If the rough opening height is 99 inches, the required door height is 96 inches (99″ – 3″ = 96″).

If you are framing the rough opening for a new door, reverse the measurements:

• Add 2 inches to the desired finished door width.
• Add 3 inches to the desired finished door height.

Importance of Larger Rough Openings

The rough opening needs to be larger than the door and its jamb for several reasons:

1. Adjustment Space:
   • Additional space allows for adjustments to ensure the door and jamb fit properly.
   • Stud wall structures may not be perfectly plumb and square, so extra space lets installers shim the jamb to achieve a level and square door installation.
2. Flooring and Sill Space:
   • Extra height accommodates flooring materials above the sub-floor, such as carpeting, wood, or tile for interior doors.
   • For exterior doors, it provides space for the sill.
3. Seasonal Expansion and Contraction:
   • Walls can expand and contract with changes in humidity and moisture.
   • The extra space allows for minor adjustments to the door fit as necessary to maintain proper operation.