I am skeptical about the recommended 2-1/2" addition to the door height for an interior door rough opening (assuming only subfloor). Consider the following estimated (meaning I am unsure if they are right) measurement stack:
- 1/2" flooring cover thickness
- 1/2" clearance b/ween flooring and door roughly
- 1/8" clearance between door and jamb header
- 3/8" jamb header thickness
- TOTAL 1-1/2"
That provides for a whole inch of slack (2-1/2" recommended rough opening height minus 1-1/2" estimated allocation above). Isn't a whole inch a bit too much of a slack provision? I understand you can shim but it seems to me that a half inch to and inch would be too much of a gap for shims (OK, can use 1x lumber but still I think it is too much).
An alternative measurement stack, especially correction with my clearance provisions would be appreciated to dispel this phenomenon to me.