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I'd like to add a door into the entrance of a passageway which leads into the bedrooms. The entrance dimensions are 87 1/4 X 39 3/4 and is drywall. it seems the standard door widths are 36 X 80, so it seems I will need to add a frame. I've looked at some doors and the "assembled" height/width seems to be 1.75 inches over the doors widths - what does this mean? What would be the best method of building a frame to support a door on this size, especially the top as I have just over 6 inches I'll need to build up. What would the internal dimensions need to be to support a door 36 X 80? enter image description here

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Is this a load bearing wall? Are you comfortable with the idea of restructuring the wall to support load properly if it is? Are you aware that if don't structure the wall properly and it's load bearing that you can cause many tens of thousands of dollars of damage to your house? –  The Evil Greebo Jun 16 at 16:01
    
So you have an opening already, and you'd like to add a door? –  Tester101 Jun 16 at 16:21
    
@ TEG - not load bearing. Just going to add frame and then door to that. –  Andrew Findlay Jun 16 at 18:01
    
@ Tester101 - yes thanks –  Andrew Findlay Jun 16 at 18:02
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2 Answers 2

The recommended rough opening for a 36" x 80" door, is 38 1/2" x 82". So you're basically looking at something like this.

Door opening

Basically, you'll have to fill the purple area with framing. Which means you might have to either use thin planks on the sides, or cut into the walls to install framing.

The rough opening (blue) around the jamb (brown) will be left open, and shims will be used to make sure the jamb is perfectly level and plumb. This area will be covered by the casing, once the door is trimmed out.

Finally the door (green) will be fitted within the jamb.

The 1 3/4" you're seeing as "assembled" dimensions, includes the door, the small gap between the door and the jamb (3/16"), and the jamb itself (11/16"). This is typical of prehung doors.

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A couple of thoughts: Doors are available in different sizes. You may find it easier to work with one a little narrower, both for framing and trimming. Prehung doors are available to open to the left or right - get one that is hinged appropriately. Doors put stress on what they are attached to - make sure your framing is sturdy and properly attached to existing framing. Door jambs sometimes come overlong so you can trim them to put the bottom of the door at the height you want, to clear floor coverings etc. Installing door assembly square/plumb/level is vital for the door to work smoothly. –  user20029 Jun 16 at 17:49
    
@ tester101 - so I have 5 1/4" to build at the top. Could I use a piece of custom cut timber anchored to the ceiling for this? If so, what type of wood would work best, i.e. strong but not too heavy? –  Andrew Findlay Jun 16 at 18:07
    
You can build it up with regular 2x4s. Remember to frame it so there is a small gap above the door assembly to allow for adjustment of the assembly in the rough opening. Shim as needed when installing the door assembly. Also, if there is no suitably located framing in the ceiling above the door, there is no point in trying to nail there. Just attach the header securely to the studs at each end. Make sure the framing you put there will work to attach the drywall/trim to once the door assembly is in place. –  user20029 Jun 19 at 15:33
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I am not sure what your exact situation is but I did something very similar in my last house. We had a hallway that led to 4 bedrooms. The kitchen was right by the entrance to the hallway so it became very noisy.

Again I was right around the same dimensions as you too - think mine was about 38" wide.

What I did was install a pocket door. These come in practically any size and I remember getting a 40". In my situation I had to cut out part of my wall, create a header going across, cut out a super small section of the other side to place end of header with support blocking, and some minor drywall repair. It took a few hours total to install door. Another couple to do finish work.

On the side that the door hits I installed two pieces of trim that went to door top trim. Door went inside trim pieces. So I lost less than a half inch of hallway width. I did lose about 6 inches of hallway height - just at the entrance.

Reason why I mention the pocket door scheme is because hallways are open for a reason. You need to get furniture through. If you create another smaller door you might have trouble getting stuff in. I know when I sold my house most people didn't even notice the pocket door until we showed them and then it was them playing with it telling me it was cool. If you post some pictures I can give you an idea on how it would be framed.

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@ DMoore - pocket doors will not work. I have a bathroom on one side and a bedroom on another. –  Andrew Findlay Jun 16 at 23:20
    
Where the hallway starts, is that the beginning of the bathroom or the bedroom or are you in the middle of the room? –  DMoore Jun 17 at 16:44
    
DMoore - this is the middle of both rooms, one on each side. –  Andrew Findlay Jun 19 at 18:55
    
That is fine. If it is where the rooms meet, it is probably easier. I would need to see pictures of the room corners. But if you don't have a closet or electrical then this isn't a huge deal. –  DMoore Jun 19 at 19:04
    
added image. As you can see, bedroom to left. The bathroom is on the right. I'm going to frame per Tester101's suggestion and put a standard door in. –  Andrew Findlay Jun 19 at 19:18
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