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I'm ordering some prehung doors to replacing the doors in my home. I tried to measure quite precisely and I found that several of my rough openings are a bit smaller than the sizes available. For example, they are 31 3/4, 25 3/4, and 29 5/8 instead of 32", 26", and 30". The manufacturer I'm using can't adjust the width.

The slabs are 30, 24, and 28", and various places on the internet suggest that the jamb are probably 3/4", so it seems like there should be room, but I'm still nervous.

How much work is it going to be to make doors and 32", 26", and 30" work? Is it going to require a bunch of planing etc. ?

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  • When your size is wrong you have to order custom. Or fix the opening. I purchased a house that was built by a mobile home manufacturer all the doors were 2” short so we reframed the openings , most folks would not notice but at 6’5” and 6’8” we notice little things like this. – Ed Beal Jun 12 '20 at 14:13
  • Possibly take a picture of the rough opening. Usually a jack stud is present on each side of the opening. I have had to remove one or both of these and replace with slightly smaller thickness jack studs. 1/4” less on each gains you 1/2” greater width. – Kris Jun 12 '20 at 17:05
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Generally the size specified is the "nominal" size. The actual size is a bit smaller.

If you ordered from a big-box store, measure an in-stock 32" door of the same brand across the outside of the jamb to see if it will actually fit within your 31 3/4" opening. My bet is that it will. If there is no in-stock version, ask the sales person for the actual dimensions. BTW- don't forget to check for height, too, just to be on the safe side.

You do want a little bit of wiggle room between the door jamb and the framing so you can get the door level, plumb and shimmed, but, so long as the existing opening is square, you can get away with minimal wiggle room.

If the opening's not square, you're going to have some work on your hands, or you're going to have to cancel this order and get smaller and/or custom doors.

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  • Yes, i all depends on how much care was taken in building the wall ( R.O. ) – Alaska Man Jun 12 '20 at 17:20
  • I second the importance of the rough opening being square. If it is a parallelogram, you can have trouble even if the width measurements are OK. – Jim Stewart Jun 12 '20 at 18:00
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You should frame your openings to conform to the recommendations of the door manufacturer. If you deviate from that, you must know EXACTLY what you are doing since the chances are high that they won't fit properly or you will not be able to shim them as needed if there is not enough clearance.

If your openings are pre-framed, as you seem to have, then that's going to be a problem and you may need to do some searching of different manufacturers to find doors that will fit your openings. But this is certainly difficult to impossible.

Why can't you fix your framing? If you have gone through the trouble to remove the old doors, you have certainly exposed the current rough openings. It will be a LOT less trouble to reframe the openings than to live with poorly installed doors.

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  • My house is 125 years old. Reframing a door opening to fit a new door can present quite a challenge. Since the OP indicates "replacing" doors, he may well be in the exact same boat. If this was new construction, then it's the GC's problem to deal with reframing the openings, but that does not seem to be the case here. – FreeMan Jun 12 '20 at 12:43
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I put in some exquisitely finished solid oak doors that my wife ordered. The company could also supply a special jig for installation which allowed installation without shims. I didn't get it but I always wished I had. My rough openings had all kinds of irregularities and I was a novice. The shimming process was for me a nightmare.

The way this system works is the jig is adjusted and clamped in place. Small wood blocks (3 or 4 on each side) are affixed on the sides of the rough opening using hot melt glue, then the blocks are shaved down using a router through openings in the jig. The claim is the prehung door slips in perfectly without shims and is nailed or screwed through the blocks.

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