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OK so I got about 20 interior prehung 6-panel doors with trim from Lowe's for $50 a piece. I was buying a lot of stuff they wanted to get rid of. Now putting up 8 news doors in a house. All of the jambs are 4 inches...

Well when I bought the doors they told me that they were fine for 2x4 construction. Didn't tell me that it would be 2x4 with 1/4 inch drywall. The problem is that I have 1/2" drywall, making the jamb a 1/2 inch too wide.

Are the 4 inch jambs common and what is the easiest way to add the outer strip?

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  • I'm not sure what the problem is. Are you not putting up drywall? – Chris Cudmore Oct 7 '13 at 19:39
  • Drywall is already up and we have a couple of doors up. Jamb is 4 inches. 2x4 - is 3.5 inches wide. Then 1/2 inch drywall on each side. Leaves me 1/2 inch gap on non-hinge side. – DMoore Oct 7 '13 at 19:49
  • Can you center the door so there's 1/4" on each side and try to make the casing fit? – Chris Cudmore Oct 7 '13 at 19:59
  • @ChrisCudmore - I could on some but others will open 180 degrees and I am afraid of the hinges hitting trim if that makes sense. Also I would have to fill that 1/4 inch gap or my trim will be slanted in towards the door. – DMoore Oct 7 '13 at 20:17
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    Where they special order or clearance? I have installed many prehung doors from lowes. The instock door jamps are always 4 5/8 wide. – Justin K Oct 7 '13 at 20:26
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There is no reason that you can't make jamb extenders these are routinely used in prehung windows. The casings and whatever you use to bridge the gap to the jamb are just trim and have no structural component.

The trick is to avoid using the exact same thickness. When two pieces are meeting in a plane, it is best to have a slight reveal, an offset (usually between 1/8 and 3/16 inch). This way you have an intended step, not an almost exact match (that is never quite exact).

jamb extender

You can glue the edge of the extender to the edge of the jamb (maintaining the reveal) and pin the face of the extender to the underlying stud.

Most stock prehung doors use jambs that are 4 9/16 inches, wide enough for 2x4 framing (1.5x3.5 actually) and two 1/2 inch drywall faces.

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  • This is exactly what we did in my house where we ran into this problem. 90% of carpentry is hiding mistakes. Just use some poplar and trim nails to extend the jamb, use some wood filler and sand it lightly, and by the time you've primed and painted no one will ever notice. – Karl Katzke Oct 8 '13 at 15:12

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