How to Hang an Internal Door: Hinges, Clearances and Fire Doors

Quick Answer: A standard internal door is hung on three 100mm (4") butt hinges with a 2mm gap to the top and sides and a 5–10mm gap at the bottom (or up to 20mm over carpet), with the door swinging clear of the frame and latching cleanly. Fire doors (FD30/FD60) must be hung on three CE/UKCA-marked hinges to BS EN 1935, fitted with intumescent strips and (where required) cold smoke seals, with a maximum 3mm gap to the frame head and stiles and around a 10mm threshold gap, all in accordance with BS 8214 and Building Regulations Approved Document B.

Summary

Hanging a door looks simple and rarely is. The frame is almost never perfectly square, the door is rarely the exact size of the opening, and the difference between a door that swings shut on its own and one that springs open or binds on the carpet comes down to a few millimetres of hinge placement and a true hinge knuckle line. It is a fundamental second-fix carpentry skill, and getting the clearances, hinge recessing and latch alignment right is what separates a tidy job from callbacks.

The job splits into two clearly different worlds. An ordinary internal door is a craft job with generous tolerances — get the gaps even and the latch working and you're done. A fire door is a regulated safety component: clearances are tight and prescribed, the hinges and ironmongery must be fire-rated and correctly certified, intumescent seals must be continuous, and the gap around the door is the difference between the door holding back fire and smoke for its rated period or failing. Treat the two the same and you'll either over-engineer a cupboard door or, far worse, fit a non-compliant fire door.

This guide covers door and frame sizing, hinge selection and recessing, setting clearances, latch and handle fitting, and the specific, non-negotiable requirements for fire doors under BS 8214 and Approved Document B. It's written for a carpenter on site with a router or chisel and a packet of hinges, not for a spec sheet.

Key Facts

• Standard UK internal door sizes — 1981 × 762 × 35mm (2'6"), 1981 × 838 × 35mm (2'9") most common; also 686, 711, 813mm widths; metric 2040 × 826/926mm
• Standard hinges — three 100mm (4") steel/stainless butt hinges per door; two acceptable on light cupboard doors only
• Fire door hinges — minimum three hinges, CE/UKCA marked to BS EN 1935 (Grade 11–13), intumescent hinge pads where the door's data sheet requires
• Top hinge position — approx 150mm down from the top of the door
• Bottom hinge position — approx 225mm up from the bottom of the door
• Middle hinge — central, or 150mm below the top hinge on heavier/fire doors to resist warping
• Standard gap (head & stiles) — 2mm (a £1 coin / 2mm spacer)
• Bottom gap — 5–8mm to hard floor; up to 10–20mm over carpet/threshold
• Fire door gap (head & stiles) — 3mm maximum (typically 2–4mm), checked with feeler/gap gauge
• Fire door threshold gap — typically ≤10mm to floor; ≤3mm to a non-combustible threshold (and limited gap for cold smoke seals)
• Intumescent strips — expand at ~200°C+; 15×4mm or 20×4mm typical, fitted in groove in door edge or frame
• Cold smoke seals — required where the door provides smoke control (FD30S/FD60S), e.g. doors to escape corridors
• Self-closer — required on most fire doors; controlled door closer to BS EN 1154
• Door thickness — internal 35mm; FD30 typically 44mm; FD60 typically 54mm
• Trimming limit — most fire doors allow only a few mm trim per edge (check the manufacturer's data — typically max 3mm per long edge, varies by door)

Quick Reference Table

Detailed Guidance

Sizing the Door to the Opening

Measure the frame height and both widths (top and bottom — frames are rarely parallel) and the diagonals to check for square. Choose the nearest oversize door and plan to trim down. The rule is plane equally from both stiles to keep any lipping/veneer balanced and the door centred.

Account for the gaps in your final size: a door should finish 2mm smaller all round than the opening (3mm max for a fire door). For the bottom, decide the floor finish first — hard floor 5–8mm, carpet 10–20mm, threshold strip to suit. Mark the door against the opening with it stood in place on wedges at the correct height before cutting.

For fire doors, trimming is strictly limited. Most are built with a lippings/timber edge that allows only a small reduction — commonly a maximum of around 3mm per long edge and very little off the top/bottom — and the manufacturer's installation data sheet is the authority. Over-trim a fire door and you expose the core, breach the certification, and it must be scrapped.

Selecting and Recessing the Hinges

Use three 100mm butt hinges for a standard 35mm door; always three (never two) for heavier doors, fire doors, and any door over ~20kg. Positions: top hinge ~150mm from the top, bottom hinge ~225mm from the bottom, third hinge central (or 150mm below the top on fire/heavy doors to resist warping).

Recessing (hanging the hinges):

1. Stand the door in the frame on wedges, packed to the correct gaps, and mark hinge positions across both door edge and frame together so they align exactly.
2. Set a marking gauge to the hinge width (depth into the timber) and the hinge thickness (the recess depth — the leaf must sit flush, not proud or sunken).
3. Chop or rout the recess. A flush hinge gives a 2mm knuckle gap; recess too deep and the door is "hinge-bound" and won't close; too shallow and it springs open.
4. Pilot-drill and fix one screw per leaf first, test the swing, then fully fix.

A door that springs open is usually hinge-bound (recesses too deep) or the hinge knuckles aren't in line. A door that binds on the latch side is usually recessed too shallow. Adjust with a thin packer behind a leaf rather than re-chopping where possible.

Setting the Clearances

The classic method: hang the door, then close it onto wedges/spacers to set the gaps. Use a 2mm spacer (a coin or proper gauge) around the head and hinge/latch stiles for a standard door. The gaps should be even and parallel top to bottom — an inconsistent gap signals the frame is out of square or the door isn't planed true.

The lock/latch stile usually needs a slight back-bevel (lean the plane ~2–3°) so the leading edge clears the frame as it swings shut. The bottom gap is set by the floor finish; remember the door must clear the carpet and any thresholds without scuffing.

Fitting the Latch, Strike and Handles

1. Mark the latch height — typically 990–1000mm to the centre of the handle spindle (align with other doors in the property).
2. Bore the edge hole for the latch body (usually 22–25mm) and the face hole for the spindle (usually 16–22mm), squarely.
3. Mortise the latch faceplate flush into the door edge.
4. Close the door and mark where the latch meets the frame; mortise the strike/keep plate so the latch seats and the door pulls up snug against the stop without rattling.
5. Fit handles/knobs to BS EN 1906 (lever furniture); on fire doors all ironmongery must be compatible with the fire rating.

A door that won't latch is almost always a misaligned strike plate — file or repack the keep rather than the latch.

Hanging a Fire Door Correctly (BS 8214 / Approved Document B)

A fire door is a certified assembly — leaf, frame, intumescent seals, hinges, closer and ironmongery all working together. The carpenter's job is to install it without breaking that certification:

• Gaps: 3mm maximum around the head and stiles (checked with a gap gauge), and the threshold gap per the door's data sheet (commonly ≤10mm to floor; tighter where a cold smoke seal is fitted). Too large a gap and fire/smoke pass; too tight and the door binds.
• Hinges: minimum three, CE/UKCA marked to BS EN 1935, with intumescent hinge pads behind each leaf if the certification requires them.
• Intumescent strips in a groove in the door edge or frame, continuous and unbroken, the correct size for the rating (commonly 15×4mm or 20×4mm). They expand at high temperature to seal the gap.
• Cold smoke seals (brush or fin) where the door is rated FD30S/FD60S — typically doors onto protected escape routes/corridors.
• Self-closer to BS EN 1154 on most fire doors, adjusted to close and latch fully from any angle.
• Frame fixing: packed solid (intumescent-compatible packers, not random offcuts) and fixed at the correct centres so the frame can't distort in a fire.
• Gaps around the frame to the wall packed with the correct material as the door's certification specifies.
• No oversized cut-outs — letterplates, vision panels and locks must be those the door is certified for; cutting an unapproved hole voids the rating.

Always keep and follow the manufacturer's installation data sheet, and label/record the installation so it can be inspected. In flats and HMOs these doors are life-safety critical — see the fire safety articles below.

Frequently Asked Questions

How big should the gap be around an internal door?

For a standard internal door, aim for 2mm around the top and both sides (a parallel, even gap) and 5–8mm at the bottom over a hard floor, increasing to 10–20mm over carpet or a threshold. For a fire door the gaps are tighter and prescribed: a maximum of 3mm around the head and stiles and the threshold gap given in the door's data sheet (often ≤10mm). Uneven gaps usually mean the frame is out of square or the door isn't planed true.

Can I trim a fire door to fit?

Only within the strict limits the manufacturer specifies — typically a few millimetres per long edge and very little off the ends. The permitted reduction is on the door's installation data sheet. Over-trimming exposes the core, breaches the third-party certification and makes the door non-compliant — it would have to be replaced. Never trim a fire door "to make it fit" without checking the data sheet first.

How many hinges does a door need?

A standard internal door uses three 100mm butt hinges — top ~150mm down, bottom ~225mm up, one central. Two hinges are only acceptable on light cupboard or wardrobe doors. Fire doors require a minimum of three hinges, CE/UKCA marked to BS EN 1935, and heavy/tall doors may need a fourth. The middle hinge is often set 150mm below the top hinge to resist warping on heavier doors.

Why does my door keep swinging open by itself?

Almost always hinge-bound — the hinge recesses are cut too deep, so the closed door is under tension and springs back open, or the frame/floor isn't level so gravity pulls it open. Pack a thin shim behind the hinge leaf to bring the door off the bind, check the hinge knuckles are in a straight line, and confirm the frame is plumb. If the floor is genuinely sloping, rising butt hinges or a closer may be the answer.

Do all flat entrance doors need to be fire doors?

In blocks of flats, the flat entrance door is typically required to be a fire door (commonly FD30S — 30 minutes plus smoke seals) to protect the common escape route, under Building Regulations Approved Document B and the building's fire strategy. Requirements depend on the building, its height and layout, so always check the fire risk assessment and Approved Document B. See the related fire safety articles for HMO and flat-specific rules.

Regulations & Standards

• BS 8214:2016 — Timber-based fire door assemblies: code of practice for installation and maintenance

• Building Regulations Approved Document B (Fire safety, Volumes 1 & 2) — fire door requirements and resistance periods

• BS EN 1935 — Single-axis hinges: performance and classification (CE/UKCA marking of hinges)

• BS EN 1154 — Controlled door closing devices (self-closers)

• BS EN 1906 — Lever handles and knob furniture

• BS 476-22 / BS EN 1634-1 — Fire resistance test methods for door assemblies (basis of FD30/FD60 ratings)

• BS 8000-5 — Workmanship on building sites: carpentry, joinery and general fixings

• GOV.UK — Approved Document B (fire safety) — fire door regulatory requirements

• BSI — BS 8214 fire door installation — installation code of practice

• BWF Fire Door Alliance — trade body guidance on fire door fitting and inspection

• FIRAS / third-party certification — installer certification schemes

• HSE / GOV.UK — Fire safety in the workplace — duty-holder responsibilities

• door frames — fitting and squaring door frames and linings

• fire doors — fire door specification, ratings and certification

• first fix second fix — where door hanging sits in the carpentry sequence

• internal door fitting pricing guide — pricing door hanging and fire door installs