Final answer:
To determine an exterior door's rough opening, you generally add 2 inches to the width and 2 1/2 inches to the height of the actual door measurements.
Step-by-step explanation:
To determine an exterior door's rough opening, you need to account for the additional space required to install the door frame and ensure that the door operates properly. This includes room for shims and insulation, and space to adjust the door for plumb.
While different manufacturers may have specific recommendations, a common guideline is to add 2 inches to the width and 2 1/2 inches to the height of the actual door size to get the rough opening size.
For example, if the door itself measures 30 inches wide by 80 inches tall, the rough opening should be 32 inches wide (30 inches + 2 inches) and 82 1/2 inches tall (80 inches + 2 1/2 inches). This size adjustment allows for the door jamb, some clearance, and any necessary adjustments during installation.
It's important to check with the door manufacturer or a construction professional to ensure that you have the correct measurements for your specific situation.