Door frames, linings and casings: the difference
Three words, two products, and a fair amount of inconsistency between suppliers. The distinction that actually matters on site is whether the doorstop is planted on or machined in, and how much weight the section is being asked to carry.
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What is the difference between a door frame, a door lining and a door casing?
A lining is a plain flat board that finishes a stud or masonry opening, with a separate doorstop planted onto it. A frame is a heavier rebated section with the stop machined in, used for external and fire doors. Casing usually means the same thing as lining, often sold as a kit.
What is a door lining?
A lining is a flat board fixed inside a structural opening to line it — three pieces, two legs and a head, forming the finished reveal the door hangs in. The doorstop, the strip the door closes against, is a separate length of timber planted onto the face of the lining once the door is hung.
Planting the stop on afterwards is an advantage on internal work. It lets you set the stop against the door as it actually hangs, which absorbs a surprising amount of an opening being slightly out of true.
What is a door frame?
A frame is a heavier section with a rebate machined into it, so the stop is part of the timber rather than nailed to it. It is stronger, more weather-resistant and better able to carry a heavy leaf, which is why it is the normal choice for external doors and for fire doors, where the frame is part of the tested assembly.
The trade-off is that a rebated frame gives you no adjustment. The stop is where the machine put it, so the frame has to go in square and plumb.
So what is a casing?
In most UK supplier catalogues, casing is another word for lining, and it very often means a lining supplied as a kit: legs, head and loose stop, cut and ready to assemble, sometimes with architrave included. There is no universal distinction between the two terms, so read what is in the pack rather than inferring it from the name.
| Term | Doorstop | Typically used for |
|---|---|---|
| Lining | Planted on separately | Internal doors in stud or masonry openings |
| Frame | Rebated into the section | External doors, fire doors, and heavy or structural openings |
| Casing | Usually planted on — read the pack | Generally a lining sold as a kit, sometimes with architrave |
What are the other parts called?
- Doorstop: the strip the door closes against. Planted on a lining, machined into a frame.
- Architrave: the moulding covering the joint between the lining and the plastered wall. Cosmetic, and the thing that makes a rough opening look finished.
- Head: the horizontal member across the top of the lining or frame.
- Legs or jambs: the two vertical members.
- Threshold or sill: the bottom member, on external frames.
- Reveal: the finished face of the opening once it is lined.
What width lining do I need?
The lining width has to match the finished thickness of the wall, including the plaster or plasterboard on both faces. Too narrow and the architrave will not sit flat; too wide and the lining stands proud of the wall.
- Measure through the opening from finished face to finished face, in three places.
- Take the largest reading, since a lining can be scribed back but not stretched.
- Choose the lining width that matches or slightly exceeds it, and plane the excess flush after fitting.
Do fire doors need a special frame?
Yes. On a fire doorset the frame is part of the tested assembly, along with the seals and the ironmongery, so it must be suitable for the rating and fixed as the manufacturer's instructions require. Hanging a certified fire door leaf in an ordinary internal lining does not produce a fire door.
Common questions
Is a door lining the same as a door frame?
No. A lining is a flat board with the doorstop planted on separately, used for internal doors. A frame is a heavier section with the stop rebated into it, used for external doors, fire doors and heavier leaves.
What is a door casing?
In most UK catalogues a casing is a lining, usually supplied as a kit with the legs, head and loose stop ready to assemble, and sometimes with architrave. The terms are used interchangeably, so check what is in the pack.
How do I know what width door lining to buy?
Measure through the opening from finished face to finished face, including plaster on both sides, in three places. Take the largest reading and choose a lining that matches or slightly exceeds it, then plane it flush after fitting.
Can I use an internal lining for a fire door?
Not unless it is suitable for the rating and covered by the door's test evidence. On a fire doorset the frame or lining is part of the tested assembly, so it must be specified and fitted according to the manufacturer's instructions.
Does the architrave come with the lining?
Sometimes. Kits sold as casings often include it, and linings sold as bare timber usually do not. Read the pack contents before ordering, because matching architrave later to an existing profile is harder than buying it together.
Ready to order?
Every door lists its sizes in both imperial and metric, so you can check yours against what you measured before you commit.