HMO Conversion Cost in London (2026 Guide)

How much does an HMO conversion cost in London in 2026?

There is no single headline number, because an HMO conversion ranges from cosmetic to structural. At the light end — a house that already works spatially, needing fire doors, hard-wired alarms, room upgrades and a compliant shared kitchen — you might budget an illustrative £2,000–£4,000 per room in build works. At the heavy end, where you are adding en-suite shower rooms, reconfiguring walls, building fire compartmentation between floors and installing a new kitchen, per-room costs climb to £15,000–£30,000 or more. A typical five- or six-bed London HMO conversion therefore spans a very wide band depending on standard.

The reason the range is so wide is that an HMO is priced by compliance, not just by decoration. Two houses of identical size can cost tens of thousands apart depending on how much fire separation, sound insulation, electrical upgrading and bathroom provision the scheme needs to be licensable. The single most useful thing you can do before buying or budgeting is establish the standard the council will require, because that — not the finish — sets the true cost floor.

What does an HMO licence cost, and do I need one?

Any HMO occupied by five or more people forming two or more households must hold a mandatory HMO licence, and a large number of London boroughs run additional or selective licensing schemes that pull smaller HMOs — three or four occupants — into the net as well. The licence is a statutory fee paid to the council, and it is one of the most variable figures in the whole project: London borough HMO licence fees in 2026 commonly fall in the £900–£2,000+ range per property, and they must be renewed, typically every five years.

The licence is not a formality. To grant it the council checks the property against its HMO standards — room sizes, amenity ratios, fire safety and management arrangements — and can refuse or attach conditions if the property falls short. That is why the build specification and the licence are two sides of the same coin: you design and build to the standard, then the licence certifies that you met it. Getting the standard wrong means expensive remedial work after completion, so it belongs at the drawing stage, not the letting stage.

• Mandatory licensing: any HMO with 5+ occupants in 2+ households
• Additional/selective licensing: many London boroughs also license smaller 3–4 person HMOs
• Licence fee: commonly £900–£2,000+ per property in London, renewable (typically 5-yearly)
• The council inspects against its HMO standards before granting or renewing

How does Article 4 change the planning cost?

Nationally, converting a small family house (Use Class C3) into a small HMO for up to six people (Use Class C4) is permitted development — no planning application required. But most inner-London boroughs have removed that right across all or part of their area using an Article 4 direction, precisely to control the spread of HMOs. Where Article 4 applies, the C3-to-C4 change of use needs a full planning application, and larger HMOs (seven or more people, a sui generis use) need planning everywhere.

This matters to the budget in two ways. First, it adds a planning application fee and, more importantly, planning risk — boroughs with Article 4 directions often also apply concentration policies that refuse new HMOs where too many already exist nearby, so the consent is not guaranteed. Second, it makes the change-of-use drawings and planning statement genuinely important: a well-argued application that demonstrates the standard and addresses concentration and amenity concerns is what turns a risky consent into an approval. Assuming permitted development when an Article 4 direction is in force is the single most expensive mistake a would-be HMO landlord can make.

Which space and amenity standards drive the cost?

The biggest hidden cost driver in any HMO is the standards the property must meet, because they dictate how much building work is actually needed. National minimum room sizes set a floor — a room slept in by one adult must be at least 6.51m², and by two adults at least 10.22m², with rooms under 4.64m² not usable as sleeping accommodation — and many London boroughs set higher figures in their own HMO standards. Undersized rooms cannot simply be let, so the layout has to be designed around compliant room sizes from the start.

Amenity ratios then dictate the kitchens and bathrooms. Councils typically require a set ratio of bathrooms and WCs to occupants and a suitably sized, equipped shared kitchen, which is what pushes larger HMOs towards adding a second bathroom or a bank of en-suites. Layer on fire safety — fire doors, protected escape routes, compartmentation between floors, interlinked alarms and sometimes emergency lighting — and you have the three systems that separate a cheap cosmetic refresh from a genuine, licensable HMO conversion. Designing all three together, at the drawing stage, is what keeps the build efficient rather than reactive.

• Minimum room sizes: 6.51m² (one adult), 10.22m² (two adults); rooms under 4.64m² not usable for sleeping
• Amenity ratios: bathrooms/WCs and a shared kitchen sized to the number of occupants
• Fire safety: fire doors, protected escape route, floor-to-floor compartmentation, interlinked alarms
• Many London boroughs impose higher room-size and amenity standards than the national minimum

What do HMO drawings, change-of-use planning and building regs cost?

Separate from the build works, three professional items are needed: a measured survey and proposed HMO layout drawings that demonstrate compliant room sizes and amenity provision, the change-of-use planning application where Article 4 requires it, and building-regulations drawings covering fire compartmentation, means of escape, sound insulation and structural alterations. As an illustrative fixed-fee band these sit on top of the build, and they are the part of the project that determines whether the scheme is lawful, licensable and lettable at all.

It is best to treat this as two approvals plus a licence, all designed to the same standard. The planning consent decides whether you may use the building as an HMO; the building-regulations approval decides that the fire, escape and structural works are safe and is what building control signs off; and the licence certifies the finished property against the council's HMO standards. Designing all three from one coordinated set of drawings avoids the classic trap of a scheme that wins planning but then fails building control or licensing on room sizes or fire separation.

• Measured survey + proposed HMO layout demonstrating compliant room sizes and amenities
• Change-of-use planning application (C3 to C4, or to a larger sui generis HMO) where Article 4 applies
• Building-regulations drawings: fire compartmentation, means of escape, sound insulation, structure
• Coordination with the licence standard so the built scheme passes inspection first time

How can I keep an HMO conversion on budget?

Most HMO overspend is compliance discovered late, not materials. The reliable savings are: confirm the use class and Article 4 status before you buy, so you are not paying for a scheme the council will refuse; design the layout around minimum room sizes and amenity ratios from the first sketch, so no room has to be rebuilt to be lettable; resolve fire compartmentation and escape at the drawing stage rather than reacting to a licensing inspector; and commission one coordinated set of drawings that satisfies planning, building regs and the licence together. A cheap layout that ignores the standards is where HMO budgets — and yields — quietly collapse.