Is splitting a flat into two viable?
Feasibility depends on five things: minimum unit size (London Plan minimum 37 m² for a 1-bed/1-person, 50 m² for 1-bed/2-person studio); independent access (separate front door from common parts, not through the other flat); independent services (separate gas/electric meters or all-electric); compartmentation (FD30s separating walls and floors); and bin/cycle storage provision. Most original flats over 80 m² with two reception rooms can be split; smaller flats rarely meet minimum sizes.
Planning and freeholder consent
Creation of an additional dwelling is always a material change of use requiring full planning permission — typical fee £528 (London 2026), 8–13 week determination, refusal risk highest in Article 4 areas. Freeholder consent (Licence to Alter) is also required and often refused on shorter leases or for share-of-freehold blocks. Tenant/occupier consent (other flats in the block) may be sought. CIL liability may apply for the new dwelling.
Construction cost breakdown
Typical 90 m² flat split into 1×50 m² + 1×40 m² flats: planning + party wall + Licence to Alter £8k–£20k; full strip-out and reconfiguration including FD60 compartment floor/walls, two new kitchens, two new bathrooms, M&E split with independent meters, new entrance door for the new flat £85k–£165k. Sound insulation upgrades to Part E (Approved Document E acoustic standards for new dwellings) typically £3k–£8k.
