I'm building a shed/barn with a 6ft doorway for two 3ft doors. If I assume the doors will be exactly 3 ft each, do I need to add extra space in the framed opening to allow them to swing easily, and if so how much?

  • It depends on the type and size of jambs and the type of astragal... you need to pick that stuff out before you frame the rough opening. Commented Jun 14, 2020 at 12:53
  • I'm building it all custom, so I can fit the jams however I want. Commented Jun 14, 2020 at 20:20
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    You are asking, specifically, how wide to frame the opening. You need to plan your framing around how you will hinge the doors and what you will attach the hinges to (i.e. jambs) Building it "custom" means nothing. You still need something to hinge the doors to and you frame to accommodate that. Commented Jun 15, 2020 at 5:12
  • @JimmyFix-it The hinges will not be standard indoor hinges that attach to a jamb and sit between the door and the framing. They will be strap hinges that will attach directly to the exterior of the barn and directly to the exterior of the door. Commented Jun 15, 2020 at 21:21
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    Excellent! You should edit your hinge plan into your question, it will make answers more helpful. Also, do you plan to utilize an astragal to cover the gap where the two doors meet in the middle? That will take some space too... Commented Jun 16, 2020 at 0:44

4 Answers 4


You'll add a list of things to get your R.O.:

  • The width of both door slabs together
  • The width of both side jambs together
  • 1" gap +/- for shimming the jambs plumb inside the framing (1/2" for each side)
  • ~3/4" for slab gaps (1/4" each left, center, right)

The slab gaps may need to vary from 1/4" depending on your hinge and latch hardware. 3/16" (9/16" total) is more ideal, as it makes for better latch engagement, but requires fairly precise carpentry.

Of course, you can frame your opening and build the doors to fit it instead. Just work the same numbers.

Assuming standard outswing doors and 3/4" jambs, your 36" slabs would need:

1/2" + 3/4" + 1/4" + 36" + 1/4" + 36" + 1/4" + 3/4" + 1/2" = 75-1/4"

If, however, you don't use floating jambs, disregard the jamb thickness and the outer (1/2") gaps. You'd then simply have:

1/4" + 36" + 1/4" + 36" + 1/4" = 72-3/4"

An astragal doesn't usually add to r.o. in a simple shed scenario. It simply mounts to the face of one slab and laps over the opposing slab. There's really no need for it to be mounted to the edge of the slab. If you do want to use an astragal between the slabs for more stable latching, take that width into consideration.

Also, you mention that there's no space needed for your hinges. Even if you're using strap hinges you don't want the slabs tight to the jambs. That would be a recipe for binding and noise.

  • Excellent. Correct there are no jambs since the hinges are exterior, so the second calculation looks correct. Commented Jun 17, 2020 at 13:35

I would suggest that you purchase a set of prehung exterior shed doors that suit your design and budget. This is the simplest approach since the doors can be pre-drilled for the type of hardware (door handles, latches) that you want. The manufacturer will give you the dimensions for your rough opening which is going to be about 1 1/2 inches wider than your doors plus the jambs - although this dimension varies.


Pick your door before framing. If you search Home Depot's website you will find both 74 in. x 81.625 in. for 36" wide doors and 72 in. x 80 in. for 6' wide rough opening.

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    Pre hung doors look to be $500+ which is more than I'm willing to spend on them. So I'll have to build these myself Commented Jun 14, 2020 at 20:23

I have built lots of barn doors with 2x4 and plywood. The additional width comes down to the thickness of the doors and the type of hinges, drop on pin & strap style usually need close to 3” these are handy because the door can be removed when fully open providing the extra few inches clearance to get equipment in and out. T style are also popular not removable but take up less room still the thickness of the door affects the needed opening , is the door going to be insulated ? A thicker door will be needed,

  • How does door thickness affect R.O.?
    – isherwood
    Commented Jun 16, 2020 at 16:28
  • Where the hinges attach and with a 4” vs 2 “ you need more space for the swing and a wider RO.
    – Ed Beal
    Commented Jun 16, 2020 at 17:19

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