HMO Conversion Cost London 2026: Full Budget Breakdown
Once you know whether your property needs planning permission, the next question is what the conversion actually costs. This is the budget breakdown: light conversion vs full conversion with en-suites, per-room cost logic, fire safety works, licensing fees, and the rent uplift you are buying with all of it.
TL;DR - The Quick Answer
There are two conversion routes and the cost difference between them is large. A light conversion - shared kitchen, shared bathrooms, new fire doors and alarms, no structural work - runs roughly £40,000-£75,000 for a 4-6 bed London property. A full conversion with en-suites in every bedroom, which usually means new partition walls, extra plumbing runs and a bigger structural scope, runs roughly £90,000-£150,000 for a 5-6 bed property. On top of construction you need to budget for building regulations and fire safety works (often already included above but sometimes billed separately), a mandatory HMO licence (£900-£2,000 in most London boroughs, more in some), and a planning application if your borough has an Article 4 direction removing permitted development rights. Minimum room sizes are fixed by law: 6.51 sqm for a single occupant, 10.22 sqm for two. This article is the direct sequel to our borough-by-borough Article 4 guide - read that first if you have not already confirmed whether your property needs planning permission at all.
Light Conversion vs Full Conversion With En-Suites
Before you can price an HMO conversion, decide which route you are actually building. These are not just design preferences - they are two different construction jobs with very different costs, and they usually target different tenant markets.
Light conversion
A shared house with private bedrooms and shared kitchen and bathroom facilities. Work is mostly compliance-driven: fire doors, an interlinked alarm system, escape route improvements, possibly a second bathroom if the tenant-to-facility ratio requires it, and cosmetic refurbishment of each room. Little or no structural work. This is the cheaper, faster route and suits properties targeting young professionals or students who are used to sharing.
Full conversion with en-suites
Every bedroom gets its own shower room. This usually means new stud partitions, new plumbing and drainage runs to multiple points across the property, additional extraction, and a bigger electrical load. It commands a rent premium per room and is standard for the professional HMO market and larger 6+ bed schemes, but it costs roughly double the light-conversion route for the same property. For a wider look at when internal reconfiguration needs its own consent, see our guide on converting a house to flats, which covers the related but distinct C3-to-multiple-C3-units route.
Neither route changes the planning position on its own. Whether you need planning permission at all depends on occupant numbers and your borough's Article 4 status, not on whether you fit en-suites - see our HMO planning permission guide for the three scenarios. What the conversion route does change is your build cost, your target rent, and how much building regulations and structural work you are taking on.
Which route suits a given property is usually more about the building and the local letting market than personal preference. A tight Victorian terrace with a narrow footprint may not have the wall runs to support six separate wet rooms without eating heavily into bedroom floor areas, pushing rooms below the 6.51 sqm minimum. A wider Edwardian semi or a purpose-converted flat over a shop is often easier to fit en-suites into without compromising room sizes. Before committing to the full conversion route on the strength of a higher achievable rent, get a measured survey and check the layout actually clears the minimum room sizes covered further down this guide - a full en-suite spec that fails on room size is not a viable scheme at any budget.
Cost Tiers: Basic, Mid and High Spec
Published figures for HMO conversion costs vary considerably between sources, and London typically runs 15-30% above the national average quoted by most refurbishment guides. The ranges below are triangulated across several independent UK HMO refurbishment and property-investment sources rather than a single quote, so treat them as planning ranges rather than a fixed price for your project.
| Tier | Light conversion (4-6 bed, shared facilities) | Full conversion (5-6 bed, en-suites) |
|---|---|---|
| Basic | £40,000-£50,000 | £90,000-£105,000 |
| Mid | £50,000-£65,000 | £105,000-£130,000 |
| High | £65,000-£75,000+ | £130,000-£150,000+ |
Construction cost only. Excludes acquisition, professional fees, licensing and planning costs (see the budget checklist further down). London and inner-London figures sit at the top of these ranges; outer boroughs and properties in reasonable starting condition sit at the bottom.
| Tier | Light conversion (4-6 bed) | Full conversion with en-suites (5-6 bed) |
|---|---|---|
| Basic | £40,000-£50,000 | £90,000-£105,000 |
| Mid | £50,000-£65,000 | £105,000-£130,000 |
| High | £65,000-£75,000+ | £130,000-£150,000+ |
Source: Triangulated from independent HMO refurbishment cost guides (Renovat Construction, HMO Checker, House Manage), 2026 • Data as of 2026
Large HMOs of 7 or more bedrooms (which are always Sui Generis and always need planning permission) push well past these ranges, commonly £150,000-£250,000+, because the extra bedrooms usually come with an extension, loft conversion or more extensive structural reconfiguration rather than a simple fit-out.
What Pushes a Project From Basic to High Spec
The tier your project lands in is driven less by finish quality (tiles, taps, kitchen units) than by the state of the existing building and how much of it needs to change to get there:
- Existing services: a property with an old consumer unit, lead or lime-based plumbing, or a single distribution board will need a full rewire and re-plumb before any HMO-specific work starts, pushing the whole project towards the high end regardless of finish
- Layout efficiency: a property that already has generously sized rooms and a workable circulation pattern needs less internal reconfiguration than one where rooms must be re-split to clear the minimum room size thresholds
- Number of new wet rooms: each additional shower room needs its own drainage run, extraction and waterproofing - the more en-suites, the steeper the curve from basic to high spec within the same tier band
- Access and location: inner London properties with restricted parking, terraced streets and limited storage for materials commonly run 15-30% above outer-London equivalents for identical scope
Per-Room Cost Logic: Where the Money Goes
Thinking in cost-per-bedroom is the fastest way to sanity-check a quote. Independent refurbishment guides converge on a mid-spec per-room figure of roughly £8,000-£15,000 for a light-touch bedroom fit-out (partition work where needed, fire door, decoration, flooring, wiring for smoke/heat detection, furniture), before any en-suite is added.
What sits inside the per-room figure
The en-suite line is the single biggest lever on total cost. Adding a shower room to every bedroom in a 6-bed property adds roughly £21,000-£48,000 on top of the light-conversion base cost, which is most of the gap between the £40k-£75k and £90k-£150k tiers above. Structural work (removing chimney breasts, forming new openings, a rear extension to gain an extra bedroom) sits outside this per-room logic entirely and should be quoted separately by a structural engineer or contractor.
How Long Does an HMO Conversion Take?
Build time follows the same light-vs-full split as cost. A light conversion of a 4-5 bed property with no en-suites and limited structural change commonly takes 8-12 weeks on site. A full conversion adding en-suites to every bedroom, with the associated plumbing and electrical work, commonly takes 12-16 weeks. Where the scheme also involves a loft conversion, an extension, or significant structural reconfiguration to hit room-size minimums, allow 16-24 weeks.
None of this includes the time before the contractor starts on site. If your borough has an Article 4 direction, add the 8-13 week planning determination period (longer if the application goes to committee). Add further weeks for building regulations sign-off, sourcing a contractor, and the HMO licence inspection before you can legally let the rooms. A realistic total from decision to first tenants moving in, on a full conversion in an Article 4 borough, is commonly 5-8 months once every stage is sequenced rather than run in parallel.
Fire Safety and Building Regulations Costs
Fire safety is not optional and it is not covered by planning permission - it is a building regulations requirement assessed separately by building control, and it is also checked by the housing team when they inspect for your HMO licence. Getting it wrong is the single most common reason licence applications stall.
Two separate legal frameworks sit behind this. Building Regulations Approved Document B sets the physical construction standard - fire doors, compartmentation, escape routes. The Regulatory Reform (Fire Safety) Order 2005 separately requires the person in control of the property (usually the landlord or managing agent) to carry out and act on a fire risk assessment on an ongoing basis, not just at the point of conversion. Both apply to every HMO regardless of size, and both are checked independently of your planning position.
What's required
- FD30 fire doors to every bedroom and the kitchen
- Mains-wired, interlinked smoke and heat alarms on every storey
- Protected escape route from every bedroom to a final exit
- Emergency lighting on escape routes (larger or multi-storey HMOs)
- Fire risk assessment and fire extinguishers/blankets in the kitchen
Typical costs
Wider building regulations compliance across a full conversion (structural checks, sound insulation between lettable rooms, ventilation, drainage) commonly adds £5,000-£20,000+ on top, depending on the extent of physical alteration. See our HMO licence vs planning permission guide for how building control, the housing department and the planning department each assess the same property differently.
Minimum Room Sizes and Amenity Standards
These are not council guidance you can negotiate around - they are mandatory licence conditions under the Licensing of Houses in Multiple Occupation (Mandatory Conditions of Licences) (England) Regulations 2018, in force since 1 October 2018. A licence will not be granted, and an existing licence can be revoked, if a sleeping room falls short.
| Room use | Minimum floor area |
|---|---|
| Single occupant, aged 10+ | 6.51 sqm |
| Two occupants, aged 10+ | 10.22 sqm |
| One occupant, under 10 | 4.64 sqm |
Floor area is measured excluding any part of the room where the ceiling height is below 1.5m. A room below 4.64 sqm cannot be used as sleeping accommodation at all. Individual councils can and sometimes do apply higher local standards on top of these national minimums, so always check your specific borough's HMO standards document before finalising layouts.
Kitchen and bathroom ratios
Alongside room sizes, national amenity standards (widely applied by London councils and endorsed by the National Residential Landlords Association) set minimum shared-facility ratios: at least one bathroom per 5 occupants, and a shared kitchen of at least 7 sqm for up to 5 occupants with at least one cooker, sink and fridge provided per 5 tenants (a fridge/freezer per 4 is commonly required). These ratios are exactly why a light conversion sometimes needs a second bathroom added even without en-suites - if you are letting to 6 tenants sharing one bathroom, you are already outside the standard ratio.
Design early, not after quoting. A layout that fails the 6.51 sqm/10.22 sqm test cannot be fixed by better project management on site - it means one bedroom is lost or two rooms need combining, which changes your rent roll and your build cost simultaneously. Get room-by-room measurements checked against these standards before you commission drawings, not after.
Mandatory Licensing Fees
Every HMO with 5 or more occupants forming 2 or more households needs a mandatory licence from the council's housing team, regardless of planning status - this is a completely separate requirement, covered in full in our licence vs planning permission guide. The fee itself varies substantially by borough and by scheme type.
| Scheme | Typical London range | Notes |
|---|---|---|
| Mandatory HMO licence | £900-£1,800 | Base fee; some boroughs also charge per habitable room |
| Additional licensing | £700-£2,000 | Council-specific, only where the borough has designated a scheme |
| Selective licensing | £500-£900 | Applies to all private rentals in a designated area, not just HMOs |
Source: Independent HMO licensing fee guides and named borough fee schedules (2026); range spans several London-specific research sources • Data as of 2026
A handful of boroughs sit noticeably above these ranges. Tower Hamlets, for example, raised its additional HMO fee by roughly 75% from April 2026 and charges a base fee plus a supplement per habitable room on top - always check the current fee schedule on the specific council website rather than relying on a borough-wide average. For which boroughs currently run additional or selective schemes alongside their Article 4 status, see our full borough-by-borough Article 4 and licensing guide.
Budget the licence fee alongside the build, not after it. Councils typically inspect before granting a licence, and a property that fails on room sizes, fire safety or amenity ratios will need remedial work before the licence is issued - which is a much more expensive fix once tenants are already in place.
Planning Permission vs Licensing: Two Separate Bills
It is worth restating this clearly because it directly affects your budget line items. Planning permission (needed for a small HMO only where your borough has an Article 4 direction, and always needed for a large 7+ person HMO) and an HMO licence (needed wherever the occupant thresholds are met, with or without Article 4) are assessed by different council departments, cost different fees, and follow different timelines.
- Planning application fee: £610 for a change of use application (from April 2026); £274 for a Lawful Development Certificate confirming permitted development rights
- HMO licence fee: £900-£2,000 depending on borough and scheme (see above), covering 5 years
- Building regulations fee: roughly £400-£900 for the building control application itself, on top of the compliance works
Budgeting for only one of these is the most common costing mistake we see. For the full decision tree on which of the three you need for your specific property, read our HMO planning permission guide.
How Article 4 Changes Your Viability Numbers
Over 20 London boroughs now have an Article 4 direction covering small HMO conversions, most of them borough-wide - see the full list here. Where a direction applies, it does not add much to your direct costs (the planning fee itself is £610), but it changes your viability in three ways that matter more than the fee:
- Timeline risk: an 8-13 week determination period (longer with committee referral) sits between you and being able to let the property, during which you are paying the mortgage or bridging cost with no rental income
- Refusal risk: unlike permitted development, an Article 4 application can be refused - commonly on HMO concentration policy (many boroughs cap the proportion of HMOs within a given radius), parking, or waste management grounds
- Retrofit risk: converting first and applying for retrospective consent is a real strategy some landlords use, but if refused you may be required to revert the property to a single dwelling, undoing some of the conversion spend
Before exchanging on a property you plan to convert, confirm the Article 4 status and, ideally, look at recently approved HMO applications nearby to gauge the council's current appetite. A refused application does not just cost the £610 fee again on resubmission - it costs the void months either side of the decision.
Common Budgeting Mistakes
Most cost overruns on HMO conversions trace back to one of a small number of avoidable mistakes, not unforeseeable bad luck:
- Pricing the construction only: the licence fee, planning fee, building control fee and contingency together commonly add 15-25% on top of the headline build figure, and are routinely left out of first-pass budgets
- Designing rooms before checking minimum sizes: committing to a floor plan before confirming every bedroom clears 6.51 sqm (or 10.22 sqm for a double) means paying twice - once for the original design, again for the rework
- Assuming the licensing fee is the same everywhere: London borough fees vary by a factor of two or more, and a handful of boroughs charge a per-room supplement on top of the base fee - budget for your specific council, not a national average
- Skipping the Article 4 check before exchange: discovering after completion that full planning permission is required, in a borough where HMO applications are commonly refused on concentration policy, is the most expensive mistake on this list
- No contingency: older properties routinely reveal issues (damp, inadequate structural bearing, outdated wiring) once stripped back - a 10-15% contingency on the construction figure is standard practice, not a nice-to-have
A Note on Financing
HMO mortgages are treated as a specialist product by lenders, not a standard buy-to-let. Deposit requirements commonly cited by mortgage brokers sit around 20-25% for a small HMO (3-4 beds), rising to 25-30%+ for a standard 5-6 bed licensed HMO and higher again for large (7+) Sui Generis HMOs. Rates, criteria and available lenders change frequently and depend heavily on your circumstances, the property, and whether it is already a licensed HMO or being converted.
This is general market information, not financial advice. Speak to a mortgage broker or independent financial adviser about current products and whether an HMO conversion is the right use of your capital before committing to a purchase or a scheme.
ROI: Rent Uplift vs a Single Let
The reason landlords take on the extra complexity of an HMO is rent per room, summed across several tenants, usually beating what the same property achieves as a single-family let. Industry sources commonly cite gross HMO yields in the 7-10% range against 4-6% for an equivalent single let, which is a meaningful uplift on paper.
The gap narrows once running costs are counted. HMOs carry higher operating costs than single lets - all bills usually included, higher wear and tear, licensing renewal, more frequent turnover, and active management - commonly cited as 30-45% of gross rent, against roughly 15-25% for a single let. Several independent HMO investment guides put realistic net yields closer to 5-7% once these costs are deducted, still generally ahead of a single let on the same property but by a smaller margin than the headline gross figures suggest.
There is also a resilience argument worth weighing separately from yield: losing one tenant in a 5-bed HMO typically costs you a fifth of the rent roll while you re-let that room, whereas losing your only tenant in a single let stops 100% of the income. Treat any specific yield percentage quoted to you, by us or anyone else, as an estimate based on comparable lettings, not a guarantee - actual achievable rent depends on location, room specification, and the local student or young-professional rental market at the time you let.
Illustrative arithmetic only, not a quote or a forecast: a 5-bed property let as a single family home might achieve a certain monthly rent. The same property let room-by-room as an HMO sums five individual room rents, and even at a modest per-room rate the total commonly exceeds the single-let figure once all five rooms are occupied. The gap is the theoretical case for converting. Whether it clears your conversion cost, licence fee and higher running costs within a sensible payback period depends entirely on real rents achievable on your street, which you should verify against actual comparable HMO lettings nearby rather than a generic percentage.
Full Budget Checklist
Pulling every line item from this guide together, here is what to budget for on a typical 5-6 bed London HMO conversion, beyond the construction cost itself:
An HMO conversion in London in 2026 typically costs £40,000-£75,000 for a light conversion with shared facilities, or £90,000-£150,000 for a full conversion with en-suite bathrooms in a 5-6 bed property, construction only. Mandatory minimum room sizes are 6.51 sqm for a single occupant and 10.22 sqm for two, set by the Licensing of Houses in Multiple Occupation (Mandatory Conditions of Licences) (England) Regulations 2018. HMO licence fees in London typically run £900-£2,000 for a 5-year term depending on borough and scheme. Planning permission is required in Article 4 areas (over 20 London boroughs) and always for large HMOs of 7+ occupants (Sui Generis). Costs vary by source, property condition, borough and specification - treat all figures as planning ranges.
Frequently Asked Questions
How much does it cost to convert a house to an HMO in London?
A light conversion (shared kitchen and bathrooms, minimal structural work) for a 4-6 bed London property typically costs £40,000-£75,000. A full conversion with en-suite bathrooms in every bedroom for a 5-6 bed property typically costs £90,000-£150,000. These are construction costs only - budget separately for planning fees (if applicable), an HMO licence, and building regulations. Costs vary by property condition, specification and exact London location, and figures published by different sources differ, so treat these as planning ranges rather than a fixed quote.
What is the difference between a light HMO conversion and a full conversion with en-suites?
A light conversion keeps shared kitchen and bathroom facilities and mainly involves compliance work - fire doors, interlinked alarms, minor refurbishment - with little or no structural alteration. A full conversion adds an en-suite shower room to every bedroom, which usually requires new partition walls, additional plumbing and drainage runs, and a larger electrical load. The full conversion route roughly doubles the construction cost compared to a light conversion on the same property, commonly adding £3,500-£8,000 per room for the en-suite alone.
What is the minimum room size for an HMO in the UK?
Under the Licensing of Houses in Multiple Occupation (Mandatory Conditions of Licences) (England) Regulations 2018, a sleeping room for one occupant aged 10 or over must be at least 6.51 sqm, and a room for two occupants aged 10 or over must be at least 10.22 sqm. A room for one child under 10 must be at least 4.64 sqm, and any room under 4.64 sqm cannot be used as sleeping accommodation. Floor area below a 1.5m ceiling height does not count. Some councils apply higher local standards on top of these national minimums.
How much does an HMO licence cost in London?
Mandatory HMO licence fees in London commonly range from £900-£1,800 for the 5-year term, though this varies significantly by borough. Additional licensing schemes (where a borough has designated one) typically run £700-£2,000, and selective licensing around £500-£900. Some boroughs also charge a supplement per habitable room on top of the base fee. Always check the current fee schedule on your specific council's website, as several boroughs raised fees substantially for the 2025/26 and 2026/27 cycles.
Do fire safety works add much to HMO conversion costs?
A typical fire safety package for a 6-bed HMO - FD30 fire doors on bedrooms and the kitchen, an interlinked mains-wired alarm system, emergency lighting, and a fire risk assessment - commonly costs £3,000-£10,000. Wider building regulations compliance across a full conversion, including sound insulation and ventilation, can add £5,000-£20,000+ depending on the extent of structural work. Fire safety is assessed separately by building control and by the council's housing team when processing your HMO licence.
Does Article 4 affect the cost of converting to an HMO?
Article 4 itself does not add much in direct fees - a change of use planning application costs £610. What it changes is risk: an 8-13 week (or longer) determination period during which you have no rental income, the possibility of refusal on policy grounds such as HMO concentration or parking, and the risk of needing to revert the property if a retrospective application after conversion is refused. Over 20 London boroughs now have Article 4 directions covering HMOs, most of them borough-wide.
Is an HMO more profitable than a single let in London?
Gross yields are commonly cited in the 7-10% range for HMOs against 4-6% for an equivalent single let. However, HMOs carry meaningfully higher running costs - commonly 30-45% of gross rent against 15-25% for a single let - due to bills, higher turnover, licensing and active management. Net yields are typically closer to 5-7% once these costs are deducted. HMOs generally still outperform on yield but by a smaller margin than the headline gross figures suggest, and actual returns depend heavily on location and letting demand.
What deposit do I need for an HMO mortgage?
Specialist HMO lenders commonly require a minimum 20-25% deposit for a small HMO (3-4 beds), with most standard licensed HMOs (5-6 beds) requiring around 25%, and large or Sui Generis HMOs (7+ beds) sometimes requiring 30% or more. Rates and criteria vary by lender and change over time. This is general market information, not financial advice - speak to a mortgage broker for current products relevant to your situation.
Summary
Two decisions drive most of your HMO conversion budget: which conversion route you build (light vs full en-suite), and whether your borough's Article 4 status adds a planning application to the process. Construction cost is only part of the picture - licensing, fire safety, building regulations and contingency routinely add 15-25% on top of the headline build figure.
Before committing to a purchase or a layout, confirm three things: the Article 4 status of the property (see our borough guide), whether your proposed room layout clears the 6.51 sqm/10.22 sqm minimums, and the current licensing fee and scheme for that specific council. Get those three answers before you commission drawings or exchange contracts, and the rest of the budget in this guide should hold up.
If you are weighing an HMO conversion against other routes for the same property - a straightforward loft conversion for extra space without a change of use, or splitting the building into self-contained flats instead of a shared house - it is worth comparing the planning risk and cost of each before you commit. Our note on what happens when a house is converted into flats without planning permission is a useful companion read if flats rather than an HMO are on the table.
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