Three words, and they are easy to read as three options on one menu. They are not. Sorting that out is most of what this page does, because once you see it, a whole category of confusing quotes becomes readable.
Three words, two decisions
“Slab” and “prehung” describe what you buy. A slab is the door panel on its own. A prehung unit is a door already hung in a frame — as Lowe’s buying guide puts it, “A prehung door comes with the door and hinges already installed in a frame. The frame includes the door jambs, or legs (the vertical elements), as well as the header that forms the top of the frame and connects the jambs.” (Lowe’s)
“Full-frame” describes what the installer takes out. That is a different question, and it has its own answer.
The two are independent, and you can see it in a single manufacturer’s own words. Pella states that all its front doors come pre-hung, and also that in a replacement “the existing door, frame and trim must be removed first”. The same page separately describes “a full-frame front door installation” as replacing “the door, frame and trim all at once”, and notes that with it “the size and shape of the opening can be changed” (Pella, updated 8/17/2026). Pella’s documented replacement example shows a prehung unit being used where the existing frame and trim are removed. That demonstrates that “prehung” and “full-frame” are not opposing labels; it does not establish every possible pairing.
One more word to clear up: “insert” is a window term. Marvin defines insert replacement as installing “within the existing window frame”, where “Only the old sash, hardware, and covers are removed and replaced” and “Existing trim and siding are not disturbed” (Marvin). Renewal by Andersen describes it as “also known as retrofitting… leaving the existing frame intact” (Renewal by Andersen). On the door side, the nearest equivalent to “keep the frame” is a slab replacement. We could not find any source that defines an “insert” door replacement, so we are not going to invent one — and if a quote uses the phrase, it is worth asking what it means by it.
Why this matters to you. A quote saying “prehung” still does not tell you the full removal scope. Asking only “is it prehung?” leaves the second question unanswered, so ask both.
What unit are you buying?
A slab is the panel alone. It goes into the frame that is already in your wall, reusing that frame’s jambs, header and its existing hinge and strike locations. It is the smallest-footprint version of the job: the trim, the casing and the sill stay where they are, and nothing behind them is disturbed.
It also inherits everything about the existing frame. If the frame is out of square, the new slab will be hung in an out-of-square frame. If the jamb bottoms are soft, they stay soft. A slab is a good answer when the frame is sound and you want a different door; it is not a way of fixing an opening.
A prehung unit arrives as a door already hung in its own frame, pre-drilled and pre-hinged, ready to go into an opening. What it needs is an opening to go into — which brings you to the second question.
How much of the opening is coming out?
At one end, nothing structural comes out: the frame stays, the trim stays, the sill stays, and only the panel changes. At the other, the existing door, frame, sill, interior casing and exterior trim all come out, leaving the rough opening — the framed hole in the wall — exposed, and the new unit goes into that.
In between, jobs vary by how much trim is disturbed and put back. The practical point is that this is a question about your wall, not about the product, and the answer is driven by what is found and what you want addressed. Removing the frame means the sill area and the jamb surrounds are open and visible, which is when anything wrong there can be dealt with. Keeping the frame means those areas stay as they are.
Each step up in removal scope adds labour, adds materials to put back, and adds finishing work — and therefore adds to the price. For what any of that actually costs, see our entry door cost guide, or the patio door cost guide for sliding and French doors. We do not publish cost figures on this page, and we are not going to tell you which factor moves the number most, because we have no source for that ranking.
The two jobs our sources describe
Two arrangements are documented by the sources cited on this page. They are not the only two a quote can describe — they are the two we can show you evidence for.
| A new panel in the frame you already have | A new unit in an opening stripped back | |
|---|---|---|
| What is supplied | A slab — the door panel alone | A prehung unit — a door already hung in its own frame |
| What is removed | The old panel | The old door, frame, sill, interior casing and exterior trim |
| What stays | Frame, jambs, header, sill, interior casing, exterior trim | The rough opening |
| What it cannot address | Anything wrong with the frame, the sill or what is behind the trim; an out-of-square opening | Changes to the size or shape of the opening |
If your quote describes neither of these — a slab going into an opening where the frame is coming out, say, or a manufacturer’s own retrofit system — that is worth asking about. We found no source describing those arrangements, which is not the same as saying they do not happen. Ask the installer what is being supplied and what is coming out, in those words.
And a new or enlarged opening is a different job altogether. Pella notes that with a full-frame installation “the size and shape of the opening can be changed”. That is structural work, it is where header and framing questions live, it has its own permitting, and it is not something to settle from a web page.
What you can tell by looking
You can learn a surprising amount from your own doorway in five minutes, without tools and without taking anything apart. Look, do not open up. Do not pull trim, do not drill, do not probe into framing. What is behind the trim is found out when the trim comes off during the work, and it is a question for your estimator, not a job for you.
- Does the door latch cleanly, or does it need a shove or a lift? A door fighting its frame suggests the frame is not square any more.
- Is there daylight anywhere around the closed door? Look from inside with the exterior light behind it.
- Is there staining at the sill or at the bottoms of the jamb legs? Water marks tell you where water has been sitting.
- Is the finish failing specifically at the bottom of the jamb legs? Failure concentrated in the lowest few inches is a different signal from failure spread evenly.
- Is paint blistering, or does the wood feel soft at the surface where you can touch it? Surface only — press with a thumb, do not dig.
- Is there an overhang, a porch roof or a gutter above the door? A door with no cover above it lives a harder life than one under a porch.
- Does splash reach the threshold? Look at the ground and the step directly outside after rain.
- Does the threshold still have visible adjustment screws, and do they look like they have travel left?
Each of these is an observation with a meaning, not a diagnosis. Several of them pointing the same way is worth mentioning to whoever quotes the job, in the words you used here.
When the existing frame cannot stay
Sometimes the visible signs point at the frame itself, and this is where the scope decision gets made for you rather than by you.
Practitioners discussing rotted jamb bottoms on the Fine Homebuilding forum make three points worth repeating as opinions rather than findings: that patching a rotted jamb bottom tends to look poor and eat a large part of a working day; that splicing in a new jamb leg can approach the cost of simply replacing the unit; and that the durable fix is usually keeping water off the door in the first place — gutters and overhang — rather than choosing a different door material (Fine Homebuilding forum thread, read 26 September 2026). These are experienced views from a public discussion, not a study, and we offer them as such.
On materials, one homeowner reported that a composite door still rotted through wood components at the bottom and edges, and that they were told rot was excluded from the warranty (Houzz thread, read 26 September 2026). That is one person’s account and we are not generalising it into a claim about how fiberglass doors are built — construction varies by product line. The useful thing to take from it is a question: ask what the jamb, the bottom rail and the edges of the unit you are being quoted are actually made of, and ask what the warranty says about rot. Our door warranty guide covers how to find the document that governs your purchase, which turns out to be less obvious than it sounds.
One question we cannot answer from any source we found: whether a wet or rotted subfloor beneath a threshold can be dealt with without removing the frame. We found no source saying it can and none saying it cannot. Put it to your estimator directly rather than assuming either way.
Sill pans, flashing and water management
A sill pan is a real, manufacturer-supported component. Therma-Tru’s installation guidance includes a sill-pan installation step and notes that “A Therma-Tru sill-pan kit and flexible flashing product can help ensure the opening is water-tight. This may also be required by building codes in some areas.” The same document also treats it as optional — “If installing without a sill pan, simply apply a full bottle of sealant to the sub floor…” — and gives the flashing rule plainly: “when installing flashing, always work from the bottom up and install it in an overlapping pattern” (Therma-Tru Project Center).
Read the scope of that source honestly, because we are: its own title is “How to install a door on a new construction project”, and it contains no removal steps. It is good evidence that sill pans and lapped flashing are part of manufacturer-sanctioned door installation. It is not evidence about what can or cannot be done in a replacement, and we are not going to stretch it into one.
What is fair to say: where the frame comes out, the sill area is exposed and the question of a pan and flashing is live. Where only a slab is replaced, it is not — nothing at the sill has been opened.
Turn all of this into questions for the quote rather than conclusions: Is a sill pan included? Is flashing included, and how is it lapped? If the frame is staying, how is water managed at the existing sill? Those belong in the quote audit — see how to audit a door replacement quote, Dimension 8.
What your quote must say
Whatever arrangement your quote describes, it should answer both questions in writing, and then itemise what follows from the answers.
| The quote should state | Why it matters |
|---|---|
| What unit is supplied — a slab, or a door already hung in a frame | This is the first question. A quote that names a slab or a prehung unit has answered it |
| What is being removed — the old panel only, or the frame, sill and trim as well | This is the second question. A quote can name the unit and still leave this one unsaid |
| If the frame is staying: how the new panel is fitted to the existing hinge and strike positions | An out-of-square frame is inherited, not corrected |
| If the frame is coming out: sill pan and flashing; new interior casing and exterior trim, and who finishes them | These are the lines a quote can leave to be discovered later |
| Which trim is disturbed, and how it is made good | “Made good” can mean anything from a bead of caulk to new casing |
| What happens if damage is found once the old unit is out | An allowance, an hourly rate, or nothing at all — all three exist |
| Hardware, finish, insulation and sealing at the perimeter, haul-away and disposal | Each is a separate line that may or may not be in the price |
Every one of these maps to a row in the quote audit sheet, which is the practical place to record what each of your quotes actually says.
Permits and inspections
Local, and genuinely different from place to place. There is no national rule in either direction. Some examples, in their own words:
- Chicago, IL — the permit covers replacement “in existing openings”, and “This permit does not authorize any increase or decrease in the size of existing wall or roof openings.” (City of Chicago)
- Minneapolis, MN — a permit is required to “replace entry door in existing wall opening” and to “install entry door in new or enlarged wall opening”. Reflects the 2020 Minnesota Residential Code; the document states it is not a complete set of requirements. (City of Minneapolis)
- Bloomington, MN — “A permit is required for ALL window replacements and exterior door replacements, including the door from the garage to the house.” (City of Bloomington, 2023)
- Piedmont, CA — “You need a permit if you are replacing exterior doors or windows.” (City of Piedmont)
- Litchfield Park, AZ — exempt “if the existing window and door opening width and corresponding window/door header does not change.” (City of Litchfield Park)
- Miami-Dade County, FL — for doors without glass, “The current Notice of Acceptance (NOA) of each door used” is required, along with design pressures; new openings need drawings “signed and sealed by a design professional”. Miami-Dade County specifically, not Florida generally. (Miami-Dade County)
Check your own building department before you assume either way.
On egress, if the subject comes up: requirements come from the code edition your jurisdiction has adopted, and they differ between states. North Carolina’s 2018 Residential Code requires the egress door to be “side-hinged” with “clear width of not less than 32 inches (813 mm) where measured between the face of the door and the stop, with the door open 90 degrees (1.57 rad)” and clear height “not less than 78 inches (1981 mm)” (NC Office of State Fire Marshal). Massachusetts, under 780 CMR 51.00, Tenth Edition Residential, Chapter 3, requires two: “A primary and secondary egress door shall be provided for each dwelling unit.” — primary 32 inches clear, secondary side-hinged 28 inches with sliding permitted, 78-inch clear height (Commonwealth of Massachusetts). Confirm the edition in force where you live.
Where this leads next
Once you know which unit you are buying and how much of the opening is coming out, the next questions are what it costs and whether your quotes agree. Figures are in the entry door cost guide and the patio door cost guide. Comparing quotes line by line is the quote audit. What the warranty covers, and which document governs your purchase, is the warranty guide. Back to doors for everything else.
Last verified: 26 September 2026. Manufacturer, retailer, code and municipal sources cited above were read on that date and are linked so you can check them. Community threads are individual self-reports, labelled as such, and are not verified. Written by Chris Horton. How we research and what we will not publish: our methodology.