Cost to Convert House to HMO London 2026 | Full Guide

Converting a house to an HMO in London costs £8,000–£20,000 for a compliance-led conversion of a typical four-bedroom property, and £20,000–£40,000 or more for a larger six-bed-plus conversion that also involves refurbishment and adding rooms. The figure depends on how much fire-safety work, partitioning and kitchen or bathroom upgrading the property needs, plus the borough's licensing fees. This guide breaks the conversion into priced work packages so landlords can budget the whole project, not just the licence.

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

An HMO conversion ranges enormously because "conversion" can mean anything from upgrading an already-suitable house to fire-safety standard, through to gutting a tired terrace and partitioning it into extra lettable rooms. We price the work, not the label. A compliance-led conversion of a four-bedroom house in reasonable condition, where the rooms already exist and meet minimum sizes, typically costs £8,000–£20,000. The money goes on fire doors, a Grade D1 interlinked alarm system, emergency lighting, fire separation and any kitchen or bathroom upgrades needed for the tenant numbers. A larger or more involved conversion, six bedrooms or more, or where you are creating extra rooms with new partitions and adding a second kitchen or bathroom, runs £20,000–£40,000 or higher once general refurbishment is included. The table shows realistic whole-project ranges by HMO size, assuming a property that needs genuine compliance work rather than a token upgrade. Licensing fees, which vary by borough, sit on top and are covered later.

HMO size	Compliance-led conversion	With refurb / added rooms
4-bed (rooms exist)	£8,000 – £20,000	£20,000 – £30,000
5-bed	£12,000 – £24,000	£25,000 – £38,000
6-bed	£18,000 – £32,000	£32,000 – £50,000
7-bed+ (large HMO)	£24,000 – £40,000+	£45,000 – £70,000+

The work packages inside an HMO conversion

An HMO conversion is a bundle of separate work packages, and seeing them itemised is the only way to understand a quote or compare two. Fire doors are usually the largest single line: every bedroom, kitchen and escape-route door becomes a certified FD30S doorset or upgrade, commonly £2,500–£6,000 across a house. The fire alarm system, a Grade D1 interlinked mains-powered system with detection in every room and the escape route, runs £1,200–£3,000 installed. Emergency lighting to the escape route adds £700–£2,500 depending on the number of fittings. Fire separation and compartmentation, boxing protected routes, fire-rating ceilings and sealing penetrations so a fire in one room cannot spread, ranges £1,500–£6,000. Partitions to create or divide rooms cost roughly £1,000–£2,000 per standard wall, more for fire-rated or acoustic specifications. Kitchen and bathroom upgrades to serve more tenants, often a second kitchen or an extra shower room, add £8,000–£25,000 where required. The table summarises the packages. Few conversions need every line at the top of its range, which is precisely why a survey-led, itemised quote beats a single headline figure.

Work package	Typical London cost (2026)
Fire doors (whole house)	£2,500 – £6,000
Grade D1 interlinked alarm system	£1,200 – £3,000
Emergency lighting to escape route	£700 – £2,500
Fire separation / compartmentation	£1,500 – £6,000
Partitions (per extra room)	£1,000 – £2,000
Additional kitchen / bathroom (each)	£8,000 – £25,000

Room sizes and partitions: creating compliant lettable rooms

The single biggest driver of conversion cost is whether you are adding rooms or just upgrading existing ones, and that decision is governed by minimum room sizes. London councils enforce national minimum HMO room sizes: a room for a single adult must be at least 6.51 square metres, and one for two adults at least 10.22 square metres, with rooms under 4.64 square metres not lettable at all as sleeping accommodation. Some boroughs apply stricter local standards, so the licensing authority's figures always govern. Where you are subdividing a large reception room or a generous bedroom into two lettable rooms, you need partitions, and in an HMO those partitions are part of the fire strategy: typically 30-minute fire-rated, properly sealed at the perimeter, and acoustically treated so sharers do not leave over noise. We build these at roughly £1,000–£2,000 per wall, more for fire and acoustic specifications, and we design the layout around the minimum-size rules so every new room actually counts toward your rent roll. The trap to avoid is creating rooms that are technically built but fall below the minimum size or block light and ventilation to neighbouring rooms; an undersized room is unlettable and a wasted spend. We confirm sizes against the borough standard before a stud goes up.

The landlord ROI: why HMO conversion pays

HMO conversion is, for most London landlords, the highest-return refurbishment decision available, which is why the up-front cost is best read as an investment rather than a bill. The arithmetic is straightforward. A four-bedroom house let to a single family on an assured shorthold tenancy might achieve one rent. The same house let room-by-room as an HMO to four or five sharers typically generates 40–80% more gross rental income, because you are letting by the room in a market with deep demand from young professionals and students. Against that uplift, a compliance-led conversion of £8,000–£20,000 is frequently recovered within twelve to twenty-four months of the additional income. Even a larger £30,000–£40,000 refurb-and-convert, with added rooms, commonly pays back inside three years while permanently raising the property's income and, often, its value. The caveats matter. HMO conversions can require planning permission (an Article 4 direction removes permitted-development rights in many London boroughs), and the running compliance, annual gas safety, five-yearly electrical inspection, fire risk assessment reviews, is ongoing. But done properly, with the fire safety and room sizes right from the start, HMO conversion remains the strongest yield play in London residential property. Our landlord guidance pages set out the compliance picture in full.

Licensing fees and what else sits outside the build

Beyond the building work, an HMO conversion carries costs that landlords routinely forget to budget, and they are not trivial. The HMO licence itself is the obvious one, and its cost varies significantly by borough: London council HMO licence fees commonly run £500–£1,500 or more for a five-year mandatory licence, with some boroughs charging per habitable room. Additional and selective licensing schemes, which many London boroughs operate, can bring smaller HMOs into scope too, so always check the specific council's current scheme and fees before committing. Planning permission is the second potential cost. Where an Article 4 direction applies, you cannot rely on permitted development to convert from a family dwelling (use class C3) to a small HMO (C4), and a planning application is needed, with fees and professional drawings adding £1,000–£3,000 and time to the programme. Larger HMOs (sui generis) almost always need planning. Then there are the assessments: a fire risk assessment for the converted HMO, an Electrical Installation Condition Report, and a gas safety certificate. Budget £300–£800 for these collectively at the outset. None is large individually, but together they are the difference between a conversion that passes its first council inspection and one that triggers an enforcement notice.

Frequently Asked Questions

How much does it cost to convert a house into an HMO in London?

A compliance-led conversion of a four-bedroom London house costs £8,000–£20,000 in 2026, covering fire doors, a Grade D1 alarm system, emergency lighting and fire separation. Larger six-bed-plus conversions involving added rooms and refurbishment run £20,000–£40,000 or more, with borough licensing fees on top.

What is the biggest cost in an HMO conversion?

Fire safety is the largest cost block. Fire doors across a house typically run £2,500–£6,000, a Grade D1 interlinked alarm system £1,200–£3,000, emergency lighting £700–£2,500 and fire separation £1,500–£6,000. Where extra kitchens or bathrooms are needed, those become the single largest lines at £8,000–£25,000 each.

What are the minimum room sizes for an HMO?

Nationally, a room for one adult must be at least 6.51 square metres and a room for two adults at least 10.22 square metres, with rooms under 4.64 square metres not usable as sleeping accommodation. Some London boroughs apply stricter local standards, so always confirm against the licensing authority before partitioning.

Does converting to an HMO need planning permission in London?

It can. Where an Article 4 direction applies, common across London, you cannot rely on permitted development to convert a family home to a small HMO and must apply for planning, adding £1,000–£3,000 and time. Larger HMOs almost always need planning. Check your borough's position before starting.

Is converting a house to an HMO worth it financially?

For most London landlords, yes. Letting by the room typically raises gross rental income 40–80% over a single family let, so a compliance-led conversion of £8,000–£20,000 is often recovered within one to two years of the extra income, while permanently increasing the property's yield.

Cost to Convert a House to an HMO in London: 2026 Guide