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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.

amphibient
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2 Answers2

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I might quibble about floor thickness (3/4 for wood strip flooring), jamb thickness (closer to 5/8) and you're missing a gap between jamb and header (1/2 to 3/4), so I would add 1/4 +1/4 +1/2 to 3/4 for a 2 1/2 to 2 3/4 RO

HerrBag
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If you live in Snow country, you want at least 2 inches gap between top of your door, jam and header depending on the elevation. Snow loads can be extreme.

Neil Newcomb
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