Prehung vs Slab Door: Which to Buy for a Replacement
Standing in the door aisle wondering whether you need the whole frame or just the door? Here is how a carpenter decides, what to measure, and how to read the handing.
Prehung vs slab comes down to the jamb. A prehung door arrives hung in its own jamb with hinges; a slab is the bare door. Buy prehung when the jamb is damaged, out of square, or the door is exterior. Buy a slab when the jamb and casing are sound and you want to keep them. JMB Builders installs either across the Twin Cities metro, labor only, priced per door, quoted from photos within one business day.
- Priced per door, labor only, either type
- We check what you plan to buy before you buy it
- Quote from photos in 1 business day
- Licensed MN contractor BC809005
A prehung door is a door already hung on hinges in its own jamb. You buy the whole assembly, the old jamb comes out, the new one goes in. A slab is just the door: no jamb, no hinges, no holes for the knob. It gets fitted to the jamb you already have. Both end up as a door that swings and latches. Which one to buy depends on what is wrong with the door you have now.
The rule of thumb: if the problem is the door, buy a slab. If the problem is the frame, or the door is exterior, buy prehung. A hollow-core bedroom door with a hole in it and a fine jamb is a slab job. A front door with a rotted bottom jamb, an old threshold and no kerf for weatherstrip is a prehung job, every time. In between are the judgment calls, and a photo of the opening settles most of them.
JMB Builders installs both across the Twin Cities metro as a labor-only job. Send us photos before you shop and we tell you which to buy, what size, and which hand. Then buy it wherever you like and we install it.
What you supply
- A photo of the door from the side it swings away from, one of the hinge side of the jamb, and the bottom of the jamb if exterior
- Measurements: slab width, height and thickness; jamb width (the depth of the frame from wall face to wall face)
- For a prehung: the rough opening if you can get to it, or the old jamb's outside dimensions
- The door you decide on, after we confirm size and handing
- Paint or stain — painting is quoted as a separate line, or leave it primed and caulked and paint it yourself
What JMB supplies
- A yes-or-no on prehung vs slab from your photos, and the size and hand to order
- For a slab: hinge mortising, lock bore, edge planing, and hanging in your existing jamb
- For a prehung: old jamb out, new unit set plumb, shims, fasteners, foam, sill pan and flashing on exterior doors, casing on both sides
- Interior casing in a standard profile or matched to the rest of the house
- Painting or staining of the new door and casing when you want it done, quoted as its own line
- Photos of the finished door in your job folder
How it is priced: per door
Quoted in writing from your photos within one business day. What moves the number:
- Slab fitted to an existing jamb vs. a prehung unit replacing the jamb and casing
- Interior vs. exterior: an exterior prehung adds a sill pan, flashing, foam and exterior trim
- Hollow-core vs. solid-core or solid wood, which takes longer to plane and hang
- A slab whose hinge and lock locations do not match the jamb, so mortises have to be filled and recut
- Rot or damage at the old jamb that changes a slab job into a prehung job once we see it
- Casing: reuse the existing, standard profile, or matched to the house
- Number of doors in the same visit
Send the photos and measurements before you buy. We would rather tell you the size is wrong on Tuesday than on install day.
How long it takes
A slab fitted to an existing jamb: two to three hours. An interior prehung: an hour or two. An exterior prehung: about half a day. Several interior doors in one day.
How your project works
- 1
Send photos and measurements
The door from both sides, the hinge edge, the jamb, and the tape measure on width, height and jamb depth. Exterior doors: a close-up of the bottom of the jamb and the threshold.
- 2
We tell you what to buy
Prehung or slab, the size, the jamb width, the handing, and anything to watch for on the label. Within one business day, along with the install quote.
- 3
You buy it
Menards, Home Depot, Lowe's, a lumberyard or online. Buy the lockset and hinges at the same time so the finish matches and everything is on site.
- 4
We install it
Slab: mortised, bored, planed and hung in your jamb. Prehung: old frame out, new unit set plumb and square, sealed, cased and adjusted until it latches clean.
Situations and options
Buy a prehung when
The jamb is split at the hinges or the strike, rotted at the bottom, out of square, or painted shut. The door is exterior and the old frame has no kerf weatherstrip or a worn-out threshold. You are changing the size or the swing. Or the old door is so far from standard that no slab will fit without a lot of work.
Buy a slab when
The jamb is solid and square and the casing is worth keeping: stained trim, tile that runs to the casing, a wall you do not want to patch. The door itself is the problem: a hole, a warp, hollow-core you want to upgrade to solid, or a style change. The new slab is the same size and thickness as the old one.
What to measure for a slab
The old door's width, height and thickness, edge to edge. The distance from the top of the door to the top of each hinge, and the hinge size. The height to the center of the knob bore. Match those and the new slab drops in with minimal cutting. Send a photo of the hinge edge and we read it for you.
What to measure for a prehung
The rough opening (the framing behind the casing), width and height; if you cannot get to it, the outside of the old jamb. The jamb width, wall face to wall face: one size for a 2x4 wall, another for a 2x6. And the handing, because a prehung cannot be flipped once it is built.
Reading the handing
Stand on the side of the door that it swings away from you: outside for an entry door, in the hall for a bedroom door. If the hinges are on your right, it is a right-hand door. On your left, left-hand. Exterior doors add inswing or outswing. Write it down and check it against the label before you buy.
Prehung vs Slab Door: Which to Buy for a Replacement: questions, answered
What is the difference between a prehung and a slab door?
A prehung door comes already hung on hinges inside its own jamb, with the hinge mortises cut, the lock bored, and on exterior units a sill, threshold and weatherstrip built in. A slab is the door alone: no jamb, no hinges, sometimes no bore for the knob. A prehung replaces the whole frame; a slab is fitted into the frame you already have.
Should I buy a prehung or slab door for a replacement?
Buy a slab when the jamb and casing are solid and square and only the door is the problem: damaged, warped, hollow-core you want to upgrade, or a style change. Buy a prehung when the jamb is split, rotted, out of square or painted shut, when the door is exterior, or when you are changing the size or swing. If you are not sure, send a photo of the opening and the hinge side of the jamb and we tell you.
How do I measure for a slab door?
Measure the old door itself: width, height and thickness, edge to edge. Then note the hinge positions, measured from the top of the door to the top of each hinge, and the hinge size. Note the height to the center of the knob bore. A new slab in the same size with hinges in the same places goes in with very little cutting. If the old door is gone, measure the inside of the jamb and subtract for the gaps; better yet, send us a photo.
How do I measure for a prehung door?
You need the rough opening, the jamb width and the handing. The rough opening is the framing behind the casing, a little bigger than the door unit; if you cannot see it, measure the outside of the old jamb and tell us. The jamb width is the thickness of the wall from finished face to finished face, and the store sells one size for 2x4 walls and another for 2x6 walls. The handing is which side the hinges are on when the door swings away from you.
Which way does my door swing, left hand or right hand?
Stand on the side the door swings away from you. For an entry door, that is outside. For a bedroom door, it is in the hallway. If the hinges are on your right, it is a right-hand door; on your left, left-hand. Exterior doors also say inswing or outswing. Different stores print the handing differently, so send us a photo of the door from that side and we confirm it against the label before you buy.
Should an exterior door always be prehung?
Almost always. An exterior prehung comes with a sill and threshold, kerf weatherstrip and a jamb that matches the door, and the whole unit gets a sill pan and flashing when it goes in. Fitting an exterior slab to an old jamb means living with the old threshold, the old weatherstrip and whatever rot is under them. The exception is a solid exterior jamb from a recent install with a damaged door; then a slab can make sense, and we tell you from the photos.
Get a written quote for this job
Three photos and a sentence is enough. You hear back within one business day. Or text the photos to 763-204-2099.
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Read morePage reviewed September 24, 2026 · JMB Builders LLC, MN license BC809005 · All doors pages
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