In reference to exterior walls, how is the rough opening size for doors calculated?

The calculation of the rough opening size for doors involves taking into account the finished size of the door frame and adding a specific allowance for the structure around the door. This allowance is typically about 62 mm (or approximately 2.5 inches), which accommodates the thickness of wall framing and any necessary shimming, adjustment, and finishing materials.

When you add 62 mm to the finished size of the door, you create a rough opening that is larger than the door frame. This additional space ensures that the door can be properly installed, allowing for enough room to adjust and align the door correctly and to provide for any padding or finishing trim that may be added around the frame. This practice helps to prevent issues with the door operation and ensures that it swings freely without binding against the frame or the wall.

Thus, using the finished size plus 62 mm is the standard method for determining the appropriate rough opening size for a door, ensuring proper fit and functionality within the wall structure.