I recently put a new door into my existing front interior door opening, but it used a standard jamb size. The existing doorway was much wider, as the original owner kept the original wood siding on, plus added foam insulation and vinyl siding on-top of that. when I placed the new door in, I kept the back side of the door jamb flush with the inside of the door, so that the trim on the inside of the house would match back up (its an old plaster and lathe house, and didn't want to do a bunch of patch work on it).

Now, on the exterior side, there is a gap between where the doorjamb ends, and where the vinyl siding starts. To cover it from the front, I placed a 2x4 face-wise into the opening, leaving a smaller gap between the back of the 2x4 and the door jamb (about a 3/4" gap).

Since I don't want to remove the door and risk damaging the plaster on the interior, my plan is to put the jamb extension on the OUTSIDE of the door. I know this isn't conventional, but since the transition already sticks out the needed space, I think I can put the jamb on the exterior side flush enough so that I can put brick-moulding on it and cover up any gaps between the brick molding and the original siding. Since jchannel will butt right up next to the brick molding, followed by siding, I think that will work.

Considering the situation, is that the best option?

If I am able to include pictures, and some are needed to explain better, I will be happy to provide some.

Here are the pictures:

This is looking outside, facing the left hand door jamb

Here is another picture. It's the best I can get you at the time as I am not at home. It's from the outside (door swings in)

Updated image

Edited:: The after




In the first two, I hadn't extended the original siding yet. The last one shows how it looks now (Except the second light is now mounted)

  • These aren't the best pictures, but.. the gap between the 2x4 in the front and the front of the jamb is the old wood siding. I am considering cutting the threshold flush at the bottom (where it tapers out around the current jamb), and adding the jamb to the front of it, thus filling in the gap (after I remove the 2x4 that wont be needed)
    – Ex0r
    Nov 10, 2017 at 15:24
  • You're not asking a very specific question, but for me to answer with confidence I'd want to see the interior and exterior trim situations. I wonder why you can't put the extension jamb to the interior just as you've put the standard jamb in place.
    – isherwood
    Nov 10, 2017 at 15:28
  • IMHO, it is a big mistake holding the door frame to the inside. There is a part of the framing exposed more than needs to be from the jamb AND SILL falling short of the siding line.
    – Jack
    Nov 10, 2017 at 15:53
  • @isherwood To answer your question, because the house is old, and it's no longer 100% square. It's easier to cover up a gap between the exterior and the back of the brick molding using the jchannel and siding than it is to cover up a gap between the wall and the interior trim. The way it sits now, the interior trim is flush with the wall like it should be.
    – Ex0r
    Nov 10, 2017 at 16:14
  • @Jack I am not sure what you mean by holding it to the inside. The doorframe is attached to the rough opening of the home. The opening is standard size, they just never removed the original siding so the protruding part on the exterior is wider than the jamb. If I removed all the vinyl siding and then all the wood siding, then reattached the vinyl siding the door jamb would fit exactly how it should.
    – Ex0r
    Nov 10, 2017 at 16:15

1 Answer 1


There wasn't an answer on this post, only a bunch of comments, so I had to create a new answer to it. I was able to get this by removing the old 2x4s and ripping down filler pieces to go in between the jamb and the exterior face boards. It turned out really nice and is all buttoned back up.

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