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What approach can be used to fabricate and install a door jamb on a 2.5" thick wall? The wall is composed of 2x4 on side (1.5") and two sheets of 1/2" drywall.

Edit: I have an old 5 panel door that fits the rough opening and old casing that I'd like to use if I can.

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I can think of two options using the prehung doors available in HI stores:

You can pull the door apart (they come in two pieces for the installation) and cut about 3/4" off of the inset part of the door. Since this side goes into the channel on the other half of the door, you'll never see it if the cut isn't pretty. I believe there's at least 1/4" of play in that channel, but measure first.

Second option is to get some strips of 1/2" wood to install behind the trim around the door. Hang the door as you normally would, but leave it 1/2" out from the walls. Then, before nailing the trim into the wall, place the 1/2" strips of wood behind the trim around the doorway.

The first option is a bit tricky since the door is very weak when disassembled and the trim makes the corners difficult to cut around. The second option comes in handy when you realize the problem after you've already installed the door (we all forget to measure first sometimes), but I don't think it looks as good to have trim sticking out like that.

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  • I may be having trouble visualizing but in the first option it sounds like you're describing adjusting the size of a door rather than making/installing a jamb for a thin wall. Can you please clarify?
    – jlpp
    Commented Jun 3, 2011 at 2:33
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    @jlpp: he's talking about a split-jamb door, I believe. The jamb has two parts; the stop is attached to one side, and the other side slides in behind it. See here
    – Niall C. ♦
    Commented Jun 3, 2011 at 2:42
  • Niall C nailed it. If you go to a HI retailer, it will be difficult to find any other type of door for an interior install, these are pretty much the default. There's a technique to installing them, so if you don't find a good tutorial online, be sure to ask.
    – BMitch
    Commented Jun 3, 2011 at 2:59
  • I added an edit to the question. I have a door and casing that I'd like to use. In this scenario, would it make sense to put together a custom door frame?
    – jlpp
    Commented Jun 3, 2011 at 11:35
  • For using an older non split-jamb door, you can use the second option. Just realize that the trim will look thicker than other doors because of the extra 1/2" strip.
    – BMitch
    Commented Jun 3, 2011 at 11:40
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I saw this posting today and thought of this question. What about just finishing the opening and using a sliding door?

http://freshome.com/2011/06/03/ingenious-door-sliding-system-for-saving-valuable-space-in-your-home

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  • Nice idea. This wall doesn't have the space for it but I'll keep it in mind for future consideration. Thanks.
    – jlpp
    Commented Jun 5, 2011 at 13:08
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I decided to try building my own jamb since I had some boards, some casing, and a door already. Not sure if I did it in the best way but it looks and works ok so far. I ended up using some lengths of 3/4" poplar and ripping them down to 2.5". I cut the side jambs to be an inch shorter than the rough opening and the top jamb (lintel?) to be 1/2" narrower than the rough. This leaves ~1/4" around the jamb for squaring and plumbing. I then measured for the hinges, allowing for 1/8" on the top and sides of the door for expansion. Translating this measurement to one of the side jambs, I made three mortises for the hinges. Then I butted the side jambs into the top jamb and screwed them together. I then put the assembled jamb into the rough opening and leveled the top, shimming where necessary. Then I plumbed one jamb with shims and measured the distance between jambs to get the second plumb, top to bottom, again using shims. Once everything was square I put screws into the jambs, through shims, into the wall studs. Finally I installed the hinges on the jamb and then had help holding the door and installing the hinges to the door. Altogether it turned out pretty well. The door gap is not perfectly even on the top jamb. I think that's because the boards I used for the jamb were not perfectly flat.

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