Doors and Windows - Meaning of rough opening

Not much experience with doors. I'm enclosing a carport and pouring a 9" concrete curb all around except at the garage doors and swing doors. I plan on prehung steel for the swing doors. Before I pour the curb, I want to make sure I have the measurements right.

The sill plate and studs will be on top of the curb. That is, there will be a 9" high concrete edge at the bottom of the door opening. Does the door side of the curb need a stud or something between the door frame and curb to mount the prehung door frame, or can it be mounted directly to the concrete?

Does the rough opening measurement on prehung doors tell me the exact space I need to leave in the curb and framing where I will install the door?

Thanks!

IMO the distance between your curb should be exactly the same width as the rough opening above the curb. This assumes that the wall on top of the curb will be flush with the face of the curb, and that the trim around your doors will then mount to the face of both the curb and the wall.

On the garage doors, I would plan to install a jamb inside the rough opening (this WILL extend to the ground) to create a finished opening for the garage door that would then only need a garage door weatherstrip. So I'd make the rough opening 1 1/2" wider than the door, and 3/4 taller.

For your entry door, the rough opening should be 2 - 2 1/2" wider than your door is. (roughly 38 1/4 for a 36" door to allow 3/8" per side)

Exactly what I needed to know. Thanks!

The architect didn't specify the garage door jamb for weatherstripping. One one side of both doors there's an existing 6x6 (the carport is a pole barn-type construction), but not on the other. Florida requires 2x6 buildout framing on the inside of the Miami-Dade garage door openings, but that will be handled by the installer. I assume that's where the weatherstripping will attach, but I'll check.

So for swing doors the rough opening should be 2-1/2" wider? I'm looking at a door on the internet that specifies 38" rough opening for a 36" door. Do you recommend the extra half inch?

If you re-read...X said 2 - 2 1/2" and roughly 2 1/4". I like 2 1/4" as well. Easily covered up by trim, but gives plenty of room for adjustment, shims, and spray foam insulation nozzle.

A 38" RO only gives 1/2" total (1/4" per side). The extra 1/4-1/2" doesn't seem like much, but it can be just what you need at times.

Yep, that's the gist of it. I like to have 2 1/4. If the rough opening is perfectly plumb, 2" would be fine. But somewhere in the 2 to 2 1/2" range is good.

Getting back to swing door rough openings, how much extra should I add to the door size (prehung) for height? In other words, the header should be how far above the slab surface?

82 1/2" is common, and will give you roughly 3/4" of space between the top of your door jamb and the bottom of the header. If I'm framing the opening I like to go 82 1/4 because I don't like such a big gap. Uses too many shims.

1/2" more than the height of the installed door frame should be plenty. No structural fasteners normally from top of frame to header, so really don't need much..just enough room for insulation. Sometimes I'll counter sink and put one screw in, or just a couple of finish nails through some shims, but you don't want to bow the top of the frame.

I can't really say "exactly this much" since there is some variation between types and manufacturers of doors. I've seen from 82 to 83 for a nominal 80" door. Also depends on inswing or outswing.

Measure your door from bottom of sill to top of frame, and add 1/2". That will be the minimum amount of room you need from the concrete to the header.