You may be confusing casings with jambs. It would be unusual to change jambs and leave in the original cheap doors.

Since you don't like the doors to begin with, by all means change them.

Whether you use pre-hung or doors alone largely depends on who's doing the labour. I'm old school and can't see replacing jambs and casings that are perfectly fine. But whether I'm installing them or having them done, from scratch definitely takes longer than ripping out the old and setting in a pre-hung unit.

For instance, many older doors are not standard sizes. So if you start with a typical hollow slab, you may have to reduce the width and height of each door, then glue them back together. Jambs may have to be recut and filled to accommodate the new locks.

OTOH, with pre-hung doors, you have to paint the jambs and casings and caulk and paint the intersection with the wall.

Are you wanting new doors or do you just want what you have to work better? A poorly closing door doesn't always mean replacement. Have someone come in and look at what you have. They may be able to make some minor changes and get the existing doors working properly.

Sometimes a hinge adjustment will help the existing doors close properly.

I used to do door installation/repair as part of my remodeling business.

You did not include enough info to make a good recommendation.

Is the problem caused by settling of the house, improper door?frame installation, moisture causing door warpage, or cheap doors degrading?

There are several possible corrections.

Replace the doors with prehung assemblies---can be expensive.

Rehang the current doors/frames---simply uninstall the existing door frames and reinstall plumb and square. Usually less expensive due to not needing new doors---but useless if not done correctly.

Replacing door slabs(leaving the old frames.---usually the most expensive method, due to more labor costs.

I meant to say casings, not jams, The doors cannot be closed tightly, even pulling on the door knob will no longer close the door. When we first moved in a year ago, you could close the doors if you pulled on the door hard, or shoved it closed on the other side of the door.

As others have noted, if it's function alone you want to improve, the doors can definitely be adjusted with sometimes surprisingly small changes. (That's assuming there are no major changes going on in the house and the frames are still pretty much plumb and level. Usually, all you need is to move the receiver plate a bit so the latch catches.

A trim carpenter or a capable handyman used to working with old homes--if there is such a thing anymore--can do the job.

Post some pics.

This post was edited by worthy on Fri, Oct 18, 13 at 19:32

Sounds like a simple adjustment of the stop should fix them.

My house was built in 1952. Not one interior door closes properly. Would I be better off to just buy doors, or buy pre-hung doors. The woodwork around the existing doors is fine. I think the door jams were replaced at some time.

Just have them adjusted so they work. There are lots of tweaks a capable guy can do. I just did 8 doors in a 40's-era house that would be rented. The owner's (who were about to move overseas for a couple years), had one regret when I was done...that they didn't do it sooner so they could have enjoyed them earlier.

Where do you live? I live in Texas; and when it gets really really dry our bathroom door doesn't close properly along with other problems (cracks in walls, etc.), even though we water lawn and foundation regularly. Do the doors close during winter when it is colder?

If you like the doors then have someone adjust them so they function to your satisfaction.

There are many tweeks that can be done.

As others have stated it might be something simple.

I personally don't like pre-hung because I've found that most have been forced through jigs at the factory and once popped lose from there packaging don't fit too well.

New slabs to fit the old openings would be my preferred way to go if you want new doors.

If the doors, frames and trim look presentable, they probably just need a little attention. Have a good carpenter or handyman come in and go over the doors. Many times, the problems are simple - ham-fisted amateur repairs, latch adjustments, loose hinge screws and so forth. Try that before you go to the expense of replacing them.