Door supply is one of the most visible pieces of the millwork trade. When a builder orders doors for a production home or a light commercial fit-out, the order usually arrives as complete prehung units rather than bare slabs. Behind that delivery is a millwork operation that assembles jambs, bores hinge pockets, preps locksets, and packages the finished unit for the jobsite. The same production discipline that goes into custom cabinetry and millwork applies to doors, and the scale of that work has grown as distributors add door lines to regional facilities.
A millwork facility that prehangs doors for dealers in its market can turn around orders in days instead of weeks. Builders gain a predictable supply of consistent units, and dealers avoid stocking dozens of jamb profiles and hinge configurations. For anyone planning new construction or a remodel, understanding how this part of the supply chain works explains why prehung doors cost what they do, how long they take to produce, and where the quality control actually happens.
What a Prehung Door Unit Includes
A prehung door is a door slab already attached to its frame. The millwork shop delivers the slab, the jamb, and the hardware prep as one assembly that a carpenter lifts into a rough opening and shims level. The final fit and finish still depend on solid carpentry and trim work at the site, but the heavy lifting, hinge alignment, lockset boring, and jamb assembly, happens in the shop where jigs hold the tolerances.
Components of a prehung unit
Each part of the unit has a specific role, and each one adds handling time in production:
- Door slab: solid wood, hollow core, or composite, sized to the opening.
- Jamb legs and head: the frame pieces that surround the slab.
- Hinges: mortised into the slab edge and the jamb.
- Lockset prep: bored holes for the handle, deadbolt, and strike plate.
- Weatherstripping and stops: applied around the perimeter to seal the gap.
- Casing or brick mold: attached in the shop or shipped loose, depending on the order.
Why dealers and builders order prehung
Dealers carry fewer SKUs when they order prehung units, because hinge location, lockset prep, and jamb profile are standardized at the factory. Builders save framing time, since each opening receives a ready-to-install assembly instead of a pile of loose parts. The trade-off is planning: a prehung order must specify door size, swing direction, jamb depth, and hardware prep before production starts, and changing any of those details after the order goes in means waiting for a new production slot.
Slab Doors vs Prehung Units: Comparing the Trade-Offs
The alternative to prehung is a slab door delivered without a frame. Slabs fit into frames built on site, which suits custom openings and historic renovations where standard jamb sizes do not apply. Prehung units dominate new construction because they cut installation time and reduce the chance of field errors.
Labor and skill requirements
Hanging a slab door properly means building the frame, mortising hinges, boring for the lockset, and fitting the slab with consistent gaps. Experienced carpenters do this well, but the work is slow and unforgiving. Prehung units move that skill into the millwork shop. The same logic drives other factory-applied components in residential construction: engineered joists can arrive with factory-applied subfloor adhesive already in place, so crews skip a messy site step and get a more consistent bond between framing and sheathing.
Cost, lead time, and quality control
Slab doors cost less per unit, but the total installed price depends on the carpenter’s hourly rate and the time spent fitting. Prehung units carry higher material cost and modest lead time, with the payoff in predictable labor. Quality control also shifts: a millwork shop can reject a defective slab before it ships, while a jobsite only discovers problems after installation. The comparison below summarizes the main differences.
| Factor | Slab door | Prehung unit |
|---|---|---|
| Material cost | Lower per door | Higher per unit |
| Site labor | Frame, hang, bore on site | Shims and screws only |
| Skill required | Experienced carpenter | Standard carpentry |
| Quality control | At the jobsite | In the millwork shop |
| Best fit | Custom openings, renovations | New construction, standard sizes |
How a Door Prehanging Line Works, Step by Step
A door prehanging line organizes the work into stations. The sequence below reflects how most millwork operations run, whether the line sits inside a large distribution facility or a dedicated secondary location near a building material yard.
The prehanging process
Production follows a fixed order so that each station builds on the one before it:
- Cut and assemble the jamb: legs and head are cut to length, then joined with fasteners or adhesive.
- Mortise the hinges: hinge locations are marked from a template and routed into the jamb and the slab edge.
- Bore the lockset prep: holes for the handle, deadbolt, and latch are drilled with a door boring machine.
- Install stops and weatherstripping: the stop strips are fastened and the seals applied around the opening.
- Hang the slab: hinges are screwed into the jamb and slab, and the door is checked for fit.
- Wrap and stage: the unit is wrapped for transport and staged for shipment or pickup.
Tolerances matter at every station. A hinge mortise cut a fraction of an inch off leaves a door that binds or sags, and a lockset bore in the wrong position forces field rework. Millwork shops control this with templates, boring machines, and inspection checkpoints between stations, so a defect gets caught before the unit is wrapped instead of after it is hung.
Secondary locations and drop-ship models
Not every market supports a full door plant. Many distributors run the bulk of their door business as drop-ship orders and non-machined slabs, then add a prehanging line where demand justifies it. A secondary facility near an existing distribution center lets the operator test the market before committing to a larger plant. The same pattern shows up across millwork categories: shops that produce fireplace mantels and custom trim often start with a small fabrication space and scale with demand.
Standard Door Sizes and Rough Openings
Prehung production runs on standard sizes. Residential interior doors are most commonly 30, 32, and 36 inches wide at 80 inches tall, while exterior units run 36 inches wide and 80 or more inches tall. Knowing these dimensions helps when ordering prehung units and when framing the rough openings that will receive them.
Common residential dimensions
| Door size | Door height | Rough opening width | Rough opening height |
|---|---|---|---|
| 2 ft 6 in | 6 ft 8 in | 32 in | 82.5 in |
| 2 ft 8 in | 6 ft 8 in | 34 in | 82.5 in |
| 3 ft 0 in | 6 ft 8 in | 38 in | 82.5 in |
| 3 ft 0 in exterior | 6 ft 8 in | 38.5 in | 82.5 in |
Jamb depth and swing considerations
The rough opening is only half the story. Jamb depth must match the wall thickness, typically 4-9/16 inches for 2×4 walls and 6-9/16 inches for 2×6 walls, and swing direction has to be specified for each opening. Millwork shops confirm these details on the order form before production, because a unit built with the wrong jamb depth cannot be fixed in the field.
Lead time and inventory
Inventory levels at a millwork facility determine how fast an order ships. Facilities that stock common sizes in depth can fill orders immediately; special sizes, fire-rated doors, and custom hardware push the order into production and add lead time. Builders planning a project should confirm stock levels early, since a door line added at a secondary location usually starts with the most common sizes first and expands as the market responds.
Planning Millwork Work in New Construction and Remodels
Door supply fits into a broader millwork schedule that includes casing, baseboard, crown molding, and cabinetry. Coordinating these trades avoids the classic failure mode where doors arrive before the openings are framed square, or after the floors are finished and the units no longer fit. Small gaps and transitions show up when door and trim schedules slip, and creative interior molding details are one way to handle them cleanly.
Coordinating doors with cabinetry
Doors and cabinets often share production capacity at a millwork shop, and both need accurate site dimensions. Kitchens in particular combine cabinet fronts, drawer hardware, and door swings in tight spaces, so the millwork order should be locked before rough-in. Even small additions, such as hidden charging stations inside kitchen drawers, need to be specified before the boxes are built, because retrofitting them after installation means cutting into finished cabinets.
A practical sequence keeps the schedule predictable: frame and rough-in first, measure openings after the framing is square, then place the door and millwork order. Allow time for production and delivery, and stage the units in a dry area at the site. Doors stored on their edges in a conditioned space hold their square better than units leaned against a wall in the weather.
The demand for finished millwork tracks the pace of housing construction, and that pace now includes more first-time buyers entering the market through rent-to-own housing programs and other alternative paths. As those buyers move into new homes and remodels, the same doors, casings, and cabinet packages keep flowing through regional millwork operations. Understanding how prehung doors are made, how long they take, and what drives their cost puts a builder in a position to order with confidence instead of guessing.