Rough opening for a door

If I want to accomodate a standard 30" x 80" door prehung, what kind of rough framing do I need to do to accomodate it?
I would assume the door is 30", the door jamb will add 3/8" on each side to make it 30-3/4" assuming a 1/2" of play to level and shim the door, I should frame it with a rough opening width of 31-1/4". Height wise, the door is 80", assume again a 3/4" jamb depth, plus another 1/2" for play, also assume a tiled flooring with thinset and tile to be 1/2", we have a total height of 81-3/4". So the rough opening should be 31-1/4" x 81-3/4". Am I correct?
Thanks in advance,
MC
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The general rule of thumb is 2" taller and wider than the door, so it should be 32"X82".
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wrote:

Thank you!
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Frame interior doors named size plus 2" (a rough opening for a 2-6 door is 2-8). Standard header height is 82 1/2" although some carpenters frame them at 82. 82 1/2 will allow plenty of room for finished flooring.
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wrote:

Thank you very much!
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A quick Google search would seem to indicate that will be a little on the small side- this site recommends 32x82 3/4. ( http://ezinearticles.com/?Rough-Openings-For-Doors&id &7777 ) Most jambs are thicker than 3/8, so that explains the difference.
I don't remember what the 'standard' sizes are off the top of my head, but the best way to be SURE is call or visit your supplier, and look in the catalog or at the tag on the door, and maybe pull the tape off your belt and double check. The catalog or tag on the casing will give the RO requirements. Some prehungs require a higher opening to accommodate the the 'ears' at the top of the side jambs, since the top jamb fits into a rabbit on the sides. (This is mainly on exterior doors.)
If in doubt (like if the doors are special order), make the RO a little oversize. It is a lot easier to add shim stock, than to enlarge an opening.
aem sends...
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Oversize is worse if the trim won't cover or there is no way to nail the trim. 2 inches over door width is normal.
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I was presuming the doors would show up before you rocked the walls, of course. I have seen situations where the client decided on tile floors later, and header had to be reworked- it wasn't pretty. I have also seen custom high-end doors come in with 1" or 5/4 jambs, versus the normal 3/4". They had to replace the cripples with 1x to make them work.
Even if the rock was already done, reworking the area around the door isn't that big a deal.
But having said all that, yes, 2" is normal, and seldom a problem if you do your homework. A vendor won't get much repeat business if they supply doors bigger than spec.
aem sends....
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Yes, anything unusual you should call your supplier and ask for a rough opening. Even exterior doors often require 2 1/2" over nominal size.
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Add 2 inches both ways, if you cant make it fit in that a little less is ok too as long as its straight.
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