Internal Doors: Sizes, Styles, Materials and Fitting

Internal doors are one of the last elements specified on a renovation but one of the most impactful on how a finished space feels. They affect sound transmission, fire safety, thermal comfort, and the overall design coherence of a home. Choosing the wrong door — or fitting a good door badly — is a common and visible mistake.

Standard Sizes and Non-Standard Openings

UK standard door sizes are 1981mm high by 762mm or 686mm wide (roughly 6'6" x 2'6" or 2'3"). Most doors available from builders' merchants and DIY stores are these sizes. Older UK properties — particularly Victorian and Edwardian houses — often have non-standard openings: taller, wider, or both. Before ordering doors, measure the opening carefully (height and width in at least three places, as openings in older properties are rarely perfectly square).

Bespoke or non-standard doors are available from specialist suppliers but cost significantly more. Alternatively, standard doors can be cut down to fit narrower openings — but not by more than about 10mm per side without compromising the internal structure (particularly relevant for hollow core doors).

Solid Core vs Hollow Core

Hollow core (cardboard honeycomb filling) doors are cheap and light but transmit sound poorly, feel insubstantial, and are damaged easily. They're adequate for low-traffic rooms where cost is the priority.

Solid core doors are substantially heavier, dampen sound significantly better, and feel and perform like proper doors. The cost difference from a builder's merchant is relatively modest (perhaps £50–£100 per door). For bathrooms, bedrooms, and any door where sound privacy matters, solid core is the right choice.

Fire Doors

Building regulations require FD30 fire doors (30 minutes fire resistance) in specific locations: between a garage and the house interior; in a loft conversion (protecting the new escape route); and in houses of multiple occupation. Fire doors must be self-closing, with intumescent strips, and cannot be cut down or modified without recertification. If building regulations apply to your project, check which doors require fire rating.

Costs