Slab vs pre-hung door reference

Pick a slab or a pre-hung door from the one thing that decides it — the condition of the existing jamb.

Typical published planning values / code minimums — NOT a certified design or a compliance sign-off. Actual egress compliance and energy performance depend on your local building code (AHJ), climate zone, the exact product’s NFRC-rated U-factor & SHGC and the installation; confirm against local code and the manufacturer’s NFRC label, and consult a pro. Structural headers for enlarged openings, whole-building heat-load / HVAC sizing and code certification are set by code and a professional — not engineered here.

Your result

RecommendationSlab

SituationExisting jamb sound & square

WhyA slab (door only) reuses the good jamb and is cheaper

With Existing jamb sound & square, a Slab is usually the call — A slab (door only) reuses the good jamb and is cheaper. A slab is cheaper if the existing jamb is sound and square; a pre-hung is the reliable exterior choice. A labeled planning guide, not a verdict.

Calculator inputs

When you replace a door you are choosing between two things. A slab is the door leaf alone: you reuse the existing jamb and hinges and hang the new leaf in place. A pre-hung door is the leaf already hung in a brand-new jamb, with weatherstrip and (for exterior units) a threshold — you pull the whole old assembly and set the new one in the rough opening.

Almost the entire decision comes down to one question: is the existing jamb sound and square? If it is, a slab is cheaper, faster and less disruptive. If it is warped, rotted, out-of-square or you are changing the door size, a pre-hung is the reliable choice — especially outdoors, where a new threshold and weatherstrip matter.

Formula

This is a decision reference, not an arithmetic tool. The rule it applies:

jamb sound & square → Slab (cheaper, reuse the jamb)
jamb damaged / out-of-square / resizing → Pre-hung (new jamb, weatherstrip, threshold)

It is a LABELED planning guide — inspect the actual opening before you commit.

Worked example

Sound jamb. An interior bedroom door with a straight, solid, square jamb — the tool returns Slab: buy the leaf, transfer the hinge and knob-bore locations, and hang it. Cheapest path.

Damaged jamb. An exterior door whose jamb is water-stained and racked out of square — the tool returns Pre-hung: a new jamb resets the geometry and brings fresh weatherstrip and a sealed threshold, so the door hangs plumb and seals against the weather.

Trade-offs and what to check

Slab — cheapest and least disruptive, keeps existing trim and jamb, but demands a square, sound jamb and careful transfer of the hinge mortises and lock bore. A DIY-friendly choice indoors.

Pre-hung — costs more and disturbs the trim, but resets the whole assembly to plumb and square and includes weatherstrip and threshold. The reliable exterior choice and the right call whenever the door size changes.

Check the jamb with a level and a square at the head and both sides before deciding.
Look for rot and water damage at the sill and lower jamb of exterior doors — a common reason to go pre-hung.
Changing size? Any change to the opening means a pre-hung and possibly framing — check the door rough-opening calculator.
Match the handing and swing for either choice.

Frequently asked questions

Should I buy a slab or a pre-hung door?

If the existing jamb is sound and square, a slab is cheaper, faster and keeps the trim. If the jamb is warped, rotted or out-of-square — or you are changing the door size — choose a pre-hung, which brings a new jamb, weatherstrip and threshold. For an exterior door in an older opening, pre-hung is usually the safer call.

Is a slab door cheaper than a pre-hung?

Yes, generally. A slab is just the door leaf, so it costs less and reuses the jamb, hinges and trim. A pre-hung includes a new jamb and hardware and more labor to set. The saving only holds if the existing jamb is in good shape.

Can I put a slab in any doorway?

Only where the jamb is square and solid and the new leaf matches the size, handing and hinge/lock positions. If the jamb is damaged or out-of-square, a slab will hang and seal poorly — that is when a pre-hung is worth the extra cost.

Which is better for an exterior door?

Pre-hung is usually better outdoors because it brings a fresh, square jamb, weatherstrip and a proper threshold, which are critical for weather sealing. A slab can work outdoors only if the existing exterior jamb and threshold are sound.