Door Linings & Frames Explained

Door linings and door frames are two different things, and confusing them at the timber merchant leads to ordering the wrong product and rework on site. This guide explains the distinction, covers common sizes and materials, walks through installation, and gives 2026 UK pricing so you can budget accurately from the start.

Door Lining vs. Door Frame: What’s the Difference?

A door lining (also called a door casing in some regions) is a simple three-piece surround that lines the opening in a timber-frame or masonry wall. It consists of:

• Two vertical side jambs (legs)
• One horizontal head jamb (top)

The lining sits inside the structural opening, fixed to the surrounding studwork or masonry with screws and packers. The door is then hung directly from the lining, hinges are cut into the lining’s face or rebate.

A door frame (or door set) is a more robust, factory-machined unit, typically used for external doors or fire doors. It includes a substantial rebated section that the door closes against and is engineered to support greater weights, provide weatherseal, and offer fire resistance. Frames are usually supplied with a sill for external applications.

In practice: interior domestic doors in the UK almost always use linings. External doors and fire-rated doors use frames. A carpenter quoting for “hanging internal doors” will almost always assume linings unless specified otherwise.

Standard Sizes

UK door openings follow standard rough opening (RO) dimensions, and linings are specified to suit.

Lining Width

The critical dimension: the lining must span the full wall thickness so the face of the lining leg sits flush with the plasterboard or plaster surface on each side. Standard wall thicknesses and corresponding lining widths:

Most timber merchants stock linings in a handful of standard widths rather than every size, and sell wider boards for cutting down on site.

Lining Height and Length

• Head jamb: cut to the door width plus the housings or rebates at each end; lining sets are sold to suit a stated door width, such as 686/762 mm or 838 mm doors
• Side jambs: cut to the door height plus the head clearance and the gap at the floor; commonly sold at around 2.0–2.1 m

Standard UK imperial door sizes are:¹

• 762 × 1981 mm (2’6” × 6’6”), the most common interior door
• 838 × 1981 mm (2’9” × 6’6”)
• 686 × 1981 mm (2’3” × 6’6”), narrower, used in en-suites and WCs

Lining Materials

Softwood (Redwood / Whitewood)

European redwood (Scots pine) or European whitewood, which is a commercial grouping of Norway spruce and silver fir.² The default material for painted interior door linings. Usually supplied with a slight moisture content tolerance, allow to acclimatise for 48 hours in the building before fitting.

• Grain can telegraph through paint if not primed correctly
• Easy to cut and fix; works with standard hand tools
• Available primed or unprimed; primed is worth the small premium

MDF (Medium Density Fibreboard)

Increasingly popular for painted applications. Very stable, with no grain, giving a smooth paint finish. Heavier than softwood, which matters when handling 2.1 m lengths. Does not tolerate moisture; not suitable for bathrooms or external-adjacent openings. Also less robust for hinge fixing: pilot holes are essential to prevent splitting.

Hardwood

Oak, ash, or sapele for clear-finished (varnished/oiled) linings. Significantly more expensive. Often used in heritage properties or high-specification joinery.

Engineered / Veneered

A substrate (such as MDF or finger-jointed softwood) faced with a hardwood veneer. Good stability, lower cost than solid hardwood, used in mid-range joinery.

Lining Types

Plain lining (no rebate): the simplest form. Architrave covers the joint between lining and wall surface. The door stop, a small planted bead the door closes against, is nailed to the lining face after hanging.

Rebated lining: factory-machined with a rebate, often about 12–15 mm deep, for the door to close into (fire-check lining sets are commonly sold with a 15 mm rebate).³ More common in fire-door applications where the rebate is part of the fire seal. Slightly more expensive but a neater finish and better acoustic seal.

Pre-machined / pre-hinged lining sets: the lining is machined with hinge recesses and strike plate positions already cut to match a specific door size. Labour-saving on site; worth the premium when hanging multiple identical doors.

Costs (2026 UK Trade Prices)

As a check on the softwood figures, a 133 mm softwood lining set with stops for 762 or 838 mm doors costs about £31 before VAT (£37 with VAT) at a builders’ merchant.⁴

Installation Overview

1. Check the rough opening: the width should allow for the door, both lining legs (commonly about 28–32 mm thick each), a 2–3 mm gap each side of the door and roughly 10 mm of packing each side; the height should allow for the door, the head lining, the gap above the door and the gap at the floor.
2. Mark the centre line of the opening and work outward symmetrically.
3. Fix the head jamb first using frame fixings (75–100 mm) through the lining and packers into the lintel or head stud. Check level.
4. Fix the side jambs: plumb using a spirit level; screw through the jamb at hinge, lock, and mid-point positions into the studwork or masonry packers.
5. Check the diagonal from corner to corner, both diagonals equal confirms the opening is square.
6. Hang the door: mark and cut hinge recesses, fit hinges, offer the door up, pack as needed.
7. Fix the door stop: once door is hung and closes freely, nail the stop bead in place with the door in the closed position to guarantee a consistent gap.
8. Fix architrave: cover the joint between lining and wall surface on both sides. Mitre the corners at 45°. Align the architrave face 3–5 mm back from the lining face (the “reveal”).

Building Regulations

For fire doors (needed at the door to an integral garage, on doors from habitable rooms onto the protected stair in a house with a floor more than 4.5 m above ground, such as after a loft conversion, and in conversions to flats), the frame and lining must be compatible with the door’s fire rating. Approved Document B asks for at least E 20 (FD 20) on doors forming part of the enclosure to a protected stair in a house, and FD30 doors are commonly used there.⁵ Between a house and an attached or integral garage it asks for E 30 Sa (FD 30S), with a self-closing device.⁵ The Sa suffix means restricted smoke leakage, so that door is normally fitted with smoke seals.⁵ The frame stop or rebate must be at least as deep as the door’s test certificate requires, and any intumescent strips or smoke seals the certificate relies on must be fitted, either pre-fitted to the door edge or set into the frame rebate.⁵ Check Part B of the Building Regulations and the door manufacturer’s installation instructions.⁵

For acoustic performance, pack the gap around the lining solidly and seal it with acoustic mastic, which limits sound leaking around the door.

Getting the lining specification right before ordering saves the frustrating scenario of a carpenter on site planing down a lining that’s 20 mm too wide, or worse, returning to the merchants mid-job.