Internal Doors: Types, Sizes & How to Choose

Replacing internal doors is one of the most cost-effective ways to refresh a home. A new door immediately changes the feel of a hallway or landing, and unlike decorating, the result is physically permanent rather than something that fades or marks over two or three years.

Prices range from about £30 for a plain hollow-core flush door to upwards of £400 for a solid hardwood panelled door, with the main cost drivers being core construction, material, and whether you want glazing. Fitting adds £80–£150 per door for a carpenter, more if the frame needs adjustment or the opening is non-standard.

Door Types

Flush Doors

The simplest and cheapest option. A flush door has a flat face on both sides, typically a hardboard or MDF skin over a lightweight core. They look contemporary and clean in minimalist interiors but can feel insubstantial if the core is hollow.

Hollow-core flush: A cardboard honeycomb fills the interior. Very light, inexpensive (£30–£80), and easy to hang. The main drawback is poor sound and thermal insulation, and they’re easily damaged, a firm knock can crack the skin. Suitable for utility rooms and spaces where noise is not a concern.

Solid-core flush: The interior is filled with solid MDF, particle board, or timber. Much heavier (40–55 kg), noticeably more soundproof, and far more durable. Costs £80–£220. A worthwhile upgrade for bedrooms and bathrooms.

Panelled Doors

A panelled door has a visible frame (stiles and rails) with recessed or raised panels between. The classic 4-panel door is ubiquitous in Victorian and Edwardian terraces; 6-panel designs are common in Georgian properties.

Panelled doors are almost always solid throughout, so they offer good sound attenuation without needing to specify a solid core specifically. They suit period properties naturally but are also used in contemporary homes where a more traditional feel is wanted.

Costs range from £90–£150 for a softwood-effect moulded door (MDF skin, not real timber) to £250–£600 for a hardwood option in oak or walnut.

Glazed Doors

Any of the above door types can include glass panels, which borrow light between rooms. Useful in narrow hallways and kitchens where borrowed light makes a real difference to liveability.

A glazed door is a critical location under the Building Regulations: the glass has to break safely, which means Class 3 to BS EN 12600, or Class 2 where a pane in a door or side panel is more than 900mm wide.¹ Toughened or laminated glass meets that; clear float glass does not and is not compliant. In England the rules sit in Approved Document K, which absorbed the old Approved Document N on 6 April 2013.¹ Wales still publishes a separate Part N.²

Glazed doors cost roughly £20–£100 more than the equivalent solid door. Frosted, Georgian-bar and decorative leaded options are all available at premium.

Bi-fold and Sliding Doors

Where space is tight, awkward alcoves, under-stair cupboards, en-suite bathrooms, bi-fold or sliding doors allow a full opening without a swing arc. These are sold as complete kits with the track hardware included. Budget £150–£400 per door set.³

Standard UK Sizes

UK internal door sizes follow a set of common standards, though older properties rarely align with them.

Thickness is almost always 35 mm for hollow-core and 44 mm for solid-core or fire doors.

The 826 mm metric leaf exists because of accessibility rather than fashion. In a new dwelling, every door to a habitable room and to the room containing the WC has to give a minimum clear opening width set against the corridor it opens off: 750 mm off a 900 mm corridor approached head-on, 775 mm off a 1,050 mm corridor where the approach is not head-on, and Approved Document M notes that a standard 826 mm leaf up to 44 mm thick satisfies the 775 mm figure.⁴ Those widths bind new dwellings only. They do not apply to an extension, and swapping doors in an existing house does not trigger them, though it is worth knowing that clear opening width is measured to the face of the open door and the opposite stop, so it always comes out narrower than the leaf you ordered.⁴

Pre-1919 properties in particular have openings that rarely match any standard dimension, heights of 2,032 mm (6′ 8″) or odd widths between 700–750 mm are typical. Always measure the existing opening accurately before ordering: measure width at top, middle and bottom (take the smallest) and height on both sides (take the smallest). A joiner can trim a timber door by up to 6 mm per edge without compromising structural integrity; beyond that you’ll need a bespoke door or a new lining.

Material Comparison

Fire Door Requirements

Under Approved Document B of the Building Regulations, certain internal doors must be fire-rated. The most common trigger for domestic properties is a house converted into flats, or a loft conversion that puts a new storey more than 4.5 m above ground level.

For a standard single-family house, fire doors are typically required:

• Between an integral garage and the dwelling: minimum E 30 Sa, the modern classification behind the FD30S label, fitted with a self-closing device, with the wall and floor between garage and house at least REI 30 from the garage side.⁵
• On rooms opening onto the stairway once a conversion creates a storey above 4.5 m, where Approved Document B asks for fire doors of at least E 20 and partitions of at least REI 30, upgrading existing doors where necessary.⁵
• On any room opening onto the escape route in an HMO or converted flat

See our separate guide on Fire Doors: FD30 vs FD60 for full detail on specifications and where they’re mandatory.

What Does Fitting Cost?

A straightforward door hang, existing frame and lining in good order, standard door size, takes a carpenter 1–2 hours and costs £80–£150 per door. Fitting a new door lining as well adds another hour and £40–£80. Rehanging on an existing frame (removing old door, planing new door to fit, mortising new hinges, fitting handle) costs around the same.

Budget extra for:

• New ironmongery (hinges, handle/latch, or lock): £15–£80 per door depending on finish
• Fire door fitting (requires correct intumescent strips and smoke seals): £150–£220 per door
• Non-standard openings needing frame adjustment: £50–£150 extra
• Painting both faces and edges: £40–£80 per door if hired separately

How to Choose

Match the property’s architecture. Panelled doors in a Victorian terrace look right; flush doors look like a shortcut. Conversely, ornate panelled doors in a glass-and-steel extension look incongruous.

Prioritise weight and core in bedrooms. Solid-core doors genuinely reduce noise transfer. In a family home with teenagers or light sleepers, the premium over hollow-core pays back immediately.

Consider door furniture before buying the door. Some cheaper doors don’t have a solid-timber zone for the lock mortise, check the manufacturer’s spec sheet for lock block location. If you’re fitting a deadlock, you need a continuous solid stile, not a hollow core with a 100 mm block.

Check swing direction. Building Regulations leave most internal door swings to the designer, with one trap worth knowing: a door in a house may swing across a landing at the bottom of a flight of stairs, but only if at least 400 mm of the landing stays clear of the swing.¹ Beyond that, doors should swing away from narrow corridors and not trap anyone in a small room, and fire-escape routes have their own requirements.

The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.