Prehung Door Jamb Too Wide – Solutions and How to Fix

Pre-hung door casings generally come with the door and the surrounding trim framework, designed to basically plug-and-play. What this means is, your door and casing fit right into the frame/gap on the wall and the rest is a matter of nailing it in place. But what do you do when the frame is too wide?

If your pre-hung door is too narrow, what you have to do next largely depends on how narrow. If it’s a matter of a few millimeters, it’s nothing that a few, strategically placed shims can’t iron out. If it’s a lot more narrow than the frame, you’ll have to get innovative. 

This kind of thing happens often with new homeowners refurbishing or upgrading the cosmetic appeal of their homes. They go out and buy pre-hung doors assuming that everything is universal. Once they get home, they realize their mistake pretty quickly. 

Prehung Door Jamb Too Wide

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Carefully Measure Everything

This is a bit of a “pre” pre-hung door purchase piece of advice. But, even after you’ve made the purchase only to discover the frame is too wide, you still need to sit down and measure everything. Hanging a door isn’t something you want to get wrong. 

The slightest variation means more legwork on your part. Pre-hung doors come with a small advantage, however, because they are already fitted inside of the casing. All you have to do is remove the hinges and door so you can fit the casing inside the frame. 

For the most part, standard door widths are 32” to 36”, not including narrower doors designed for installation in closets and utility sheds. The opening, or frame the door has to fit in, should be around 38”.

Why the extra two inches for a maximum door size of 36”? Because door frames are accounting for the extra width of the casing as well. So, if you have a 36” wide door, measure the top and bottom of the door jamb to ensure they are 38”, give or take ½”.

Can You Cut a Prehung Door Jamb?

Yes, you can. If your door and casing are too large for the opening, in terms of width, you will have to. If the door jamb is too wide for the casing, however, you will have to add to the framework to narrow it down. 

When narrowing the door frame down, the only thing you may have to cut is the sheetrock, simply because it’s in the way. Most likely, you won’t have to do that either. It all depends on the location of the door jamb and what you have to do to get the frame prepped for the door and door casing. 

How Do You Narrow a Door Jamb?

There’s a lot that goes into this. In cases where the frame is just a hair too wide, you can get away with adding some shims in between the actual frame and the jamb. Simply tap them in with a hammer to narrow the opening a few millimeters, then cut the shims and sand them down. 

You can also add an extra hinge plate. Of course, both methods are only if you need to slightly narrow the opening. If you need to seriously narrow the opening, everything has to come out. That means you need to pry out the baseboards, existing trim work, and the entire jamb from along the frame. 

The jamb often has to be removed by inserting a reciprocating saw between the frame and the jamb (in the same spot you would insert the shims) and cutting the nails holding the jamb to the frame. Once the jamb is removed, the real fun begins because you have to frame a door.

This is assuming your pre-hung door only comes with a casing and not an entirely new frame. You can get either. If you have a pre-built frame, all you need to do is add enough to the existing framework, along with extra sheetrock, to accept a narrower frame. 

If you don’t have a door jamb, it’s best and cheapest to build your own, sized to accept your door casing, with the door opening narrowed to accept the door jamb.

  • Measure and insert the number of top plates, sole plates, and king studs needed (if applicable)
  • Nail your jack studs in place to narrow the door opening
  • Fit your jamb into place and secure
  • Extend your sheetrock to match the additional jack studs
  • Insert the door casing in the narrower opening
  • Mount your door

How Wide is the Jamb on a Pre-Hung Door?

That depends. Some pre-hung doors only come with a casing and not a jamb. Most times, the jamb is already in place, installed in the door opening when the home was built. Including the jam with the door, you come up with a variety of sizes, depending on the door. 

  • 28” x 80” door = 30” x 82 and ¼”
  • 30” x 80” door = 32” x 82 and ¼”
  • 32” x 80” door = 34” x 82 and ¼”
  • 34” x 80” door = 36” x 82 and ¼”
  • 36” x 80” door = 38” x 82 and ¼”

Final Thoughts

Hopefully, the only thing you’ll need to do is add a few shims between the frame and the door jamb. It’s the easiest way.

Unfortunately, it hardly ever turns out that way. If you have to do some extra, just prepare to carefully measure out everything, unless you enjoy repeating the same work over and over. 

Got the opposite problem? Read our article on what to do if your prehung door won’t close.