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Prehung vs. Slab Door: Which Should You Buy?

What a prehung unit and a bare slab each include, when your existing jamb is sound enough for a slab, and how the installed cost really compares.

Prehung vs. Slab Door: Which Should You Buy? comparison

The Bottom Line

Prehung is the doors version of a full-frame replacement; a slab is the doors version of an insert. If the jamb is dry, square and unmodified and you are keeping the same size and swing, a slab is the cheaper, faster and entirely reasonable choice. If the diagonals are off by more than a quarter inch, a screwdriver sinks into the jamb or sill, or there is water staining on interior trim, the cheaper object becomes the more expensive job, and prehung is what actually fixes the opening.

Material information and relevant data are maintained by Remodel Your Home’s editorial research team. Learn about our editorial standards.

Slab Door vs. Prehung Door Unit

Buy a prehung door if the existing jamb is rotted, racked, or you want to change the door's size. The unit arrives already hung in a new frame with a new sill and weatherstripping. Buy a slab if the jamb is sound and square, because you keep the frame and only swap the door.

When a contractor quotes a new front door they are quoting one of two very different products. A slab is the door panel by itself: no frame, no hinges mortised, no sill. A prehung unit is the door already hanging in a brand-new frame, hinges mortised at the factory, sill and threshold attached, weatherstripping in place. Everything else about the quote (labor, warranty, how long you have no front door) follows from that one choice.

Prehung is the doors version of full-frame window replacement

In windows, an insert replacement drops a new window into the frame already in the wall, while a full-frame replacement strips the opening back to the rough framing and rebuilds it. The tradeoffs are identical. A slab is the insert: you reuse the existing frame and jamb, so it is cheaper, faster, less disruptive, and completely dependent on the existing frame being sound. A prehung unit is the full-frame: new frame, new jamb, new sill. It resets the opening, which makes it the only version that fixes rot, water damage, or an opening that has shifted out of square.

The reason full-frame wins arguments in windows is the reason prehung wins them in doors: an insert or a slab inherits every problem the old frame already has, and hides it behind something new.

Slab Door Overview

Just the panel. To install it a carpenter must make the new door match the frame already in your wall: mortise the hinge gains to line up exactly with existing hinge positions, bore lockset and deadbolt holes at existing heights, trim the edges so the reveal is even on all four sides, then bevel the latch edge so the door clears as it swings.

Slabs make sense in a specific situation: the jamb is dry and solid, the sill intact, the opening square, and you are keeping the same size and swing. That is a real and common situation, especially in newer homes or where a previous owner already replaced the frame.

Prehung Door Unit Overview

An assembled system. ProVia publishes exactly what ships: the door already assembled inside the frame, a pre-finished slab and frame with matching touch-up color, pre-cut casing, aluminum cladding for the brickmold, mull covers for transoms or sidelites, a pre-installed threshold, pre-installed hinges and accessories with the lockset packed separately, and an optional installation kit with insulation, caulk, screws and shims (provia.com/doors/prehung).

The practical point: the hard alignment work (hinge placement, reveal, latch geometry, threshold seal) was done in a factory on a jig, not on your porch. The installer's job becomes setting a known-square unit plumb and level and flashing it so water leaves the building.

It also means the jamb is part of what you are buying, and jambs differ. ProVia offers four frame materials with different warranty terms: FrameSaver full wood, PermaTech composite, FusionFrame composite, and a steel L-frame. The two composite frames are warranted against rot and decay for as long as the original purchaser owns and lives in the home, while the steel L-frame and its components carry five years (ProVia entry door warranty card, 1/28/26). If your old jamb rotted once, the material of the new one matters.

Slab Door vs. Prehung Door Unit Comparison

FactorSlab DoorPrehung Door Unit
What You GetThe door panel only: no frame, no sill, hinges not mortisedDoor already hung in a new frame, with sill, threshold, weatherstripping and mortised hinges
Jamb Condition RequiredSound, square, dry and unmodifiedAny: the frame is replaced
Fixes Rot, a Failed Sill or a Racked OpeningNo. The new door inherits every problem the old frame hasYes. This is the only version that resets the opening
Typical LaborAbout 2.5 crew-hours, but precision joinery: hinge gains, lockset bores and edge fitting all cut to match the old jambAbout 4 crew-hours, a set-and-flash sequence on a factory-square unit
Can Change Size or SwingNoYes
Weather SealYou keep the existing weatherstripping, sill and thresholdNew throughout, installed at the factory
Warranty ExposureManufacturer warranties are written around complete door systems, so the water-managing parts sit outside coverageThe whole system is covered as sold
Best ForA newer opening that is demonstrably dry and square, keeping the same size and swingA rotted, racked, water-stained or previously-modified opening, or any change of size

Frequently Asked Questions

A slab is the door panel by itself: no frame, no hinges mortised, no sill. A prehung unit is the door already hanging in a brand-new frame, hinges mortised at the factory, sill and threshold attached, weatherstripping in place. Everything else about the quote follows from that one choice.

Only if the jamb is sound, square and unmodified. Rot or soft wood on the jamb legs, a cupped or split sill, a racked opening, water staining on interior trim, or a jamb that has already been shimmed or planed to fit a previous door all rule it out.

Measure the diagonals corner to corner inside the frame both ways. Square openings match within about 1/8 inch, and 1/4 inch or more means racked. Then check the hinge jamb is plumb with a 4-foot level, read the reveal for an even gap, and press a screwdriver into the bottom of both jamb legs and the sill to probe for rot.

The slab is the cheaper object. The slab job frequently is not the cheaper job, because the fitting risk sits with labor rather than materials and every 1/8 inch the old jamb is off is absorbed by hand-planing, shimming or re-mortising. You also inherit the old weatherstripping, sill and threshold, which are the exact parts that fail first.

A prehung install runs about 4 crew-hours as a set-and-flash sequence on a factory-square unit. A slab-only hang is estimated at about 2.5 crew-hours, though it adds precision joinery: hinge gains cut to match the old jamb exactly, lockset and deadbolt bored to existing heights, edges fitted and beveled. Those hours are our own internal labor estimate rather than a published industry standard.

The reason is water rather than upselling. The parts keeping water out of the wall (sill pan, threshold, flashing behind the brickmold) are all part of the frame. An installer reusing your jamb is warranting their work on top of someone else's assembly and cannot see what is behind it.

Usually yes. Manufacturer warranties are largely written around complete door systems: slab, frame, sill, weatherstripping and glass together. Buy only the slab and the parts that manage water sit outside the warranty.

A slab only works on a jamb that is sound, square and unmodified. Any one of these rules it out: Rot or soft wood anywhere on the jamb legs, especially the bottom six inches where water sits. A failing sill or threshold. The sill manages water. If it is cupped, split, or the threshold no longer seals, a new slab will not fix it. A racked, out-of-square opening. Houses settle and the reveal goes wedge-shaped. Water staining on interior trim or the floor, which usually means the flashing behind the frame has failed and needs opening up. A jamb already shimmed, planed or patched to make a previous door fit.

Five minutes with a tape, a level and a screwdriver: Measure the diagonals. Door open, corner to corner inside the frame, both ways. Square openings match within about 1/8 inch; 1/4 inch or more means racked. Level the hinge jamb. A 4-foot level against the hinge-side jamb: plumb top to bottom, no bow in the middle. Read the reveal. Closed, an even 1/8 inch gap all round is square. A tapering gap is not. Probe for rot. Press a screwdriver tip firmly into the bottom of both jamb legs, the sill and the brickmold. If it sinks in, that wood is gone. Check the latch. If the door only latches when you lift or lean on it, the frame has moved. Fail any of those and you are buying a prehung unit, whatever the sticker price says.

The slab is the cheaper object. The slab job frequently is not the cheaper job. The fitting risk sits with labor rather than materials, because every 1/8 inch the old jamb is off is absorbed by hand-planing, shimming or re-mortising. You also inherit the old weather seal: the existing weatherstripping, sill and threshold, which are the exact parts that fail first and cause the drafts most people are replacing the door to fix. Hardware rarely lines up, because older hinge spacing and lockset heights routinely differ from what a stock slab is machined for. Factory finish usually is not included either: ProVia's warranty requires primed slabs be finished with a high-quality exterior-grade paint or stain within 90 days of installation. And warranty coverage narrows, because manufacturer warranties are largely written around complete door systems (slab, frame, sill, weatherstripping and glass together), so if you buy only the slab, the parts that manage water sit outside the warranty.

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