HMO Conversion London: Planning, Building Regs and Costs

An HMO (House in Multiple Occupation) is a property let to three or more tenants who are not related and who share facilities (kitchen, bathroom, WC). The precise definition under the Housing Act 2004 is more technical, but this captures the core principle.

• Types of HMO:
• •**3–5 person small HMO**: 3–5 people sharing. May or may not require a licence depending on the council.
• •**Large HMO (mandatory licence)**: 5 or more people sharing across 3 or more storeys. Requires a mandatory HMO licence from the council.
• •**Additional licensing areas**: many London boroughs have introduced 'additional licensing' schemes covering smaller HMOs (sometimes from 3 people). Over 20 London boroughs now have additional licensing schemes covering most of their area.
• •**Selective licensing**: some London boroughs operate selective licensing for all private rented property in certain areas — distinct from HMO licensing but relevant to landlords.

**Why London HMOs require careful planning**: London is unusual in the scale of Article 4 Directions removing Permitted Development rights for HMO conversions. Most inner London boroughs, and many outer London boroughs, require a planning application to change a family dwelling (Use Class C3) to an HMO (Use Class C4 or Sui Generis for larger HMOs). This planning requirement is the most common surprise for new HMO investors in London.

**Use Classes**: a family home is Use Class C3. An HMO for 3–6 people is Use Class C4. An HMO for 7+ people is Sui Generis (no permitted development rights).

Normally (without an Article 4 Direction), changing from C3 to C4 is Permitted Development — no planning application needed. However, most London boroughs have applied Article 4 Directions that remove this PD right, meaning a planning application is required.

• **Article 4 Direction London boroughs**: the following boroughs (among others) have Article 4 Directions requiring planning permission for C3→C4 change of use:
• •Camden, Islington, Hackney, Tower Hamlets, Newham, Waltham Forest, Redbridge, Barking and Dagenham, Greenwich, Lewisham, Southwark, Lambeth, Wandsworth, Merton, Sutton, Croydon, Bromley, Bexley, Havering, Barnet, Enfield, Haringey, and many others

In practice, if your London property is in a residential borough, assume an Article 4 Direction applies and a planning application is required. Check the council's website or contact the planning department to confirm for the specific address.

• **Planning application considerations**:
• •The application must demonstrate that the HMO conversion meets the council's HMO planning policy — typically in terms of the impact on the local area (concentrations of HMOs), parking, amenity for future occupants (room sizes, shared facilities)
• •Room sizes: most London councils apply minimum room sizes for HMO planning. Typically: single room minimum 6.5m²; double room minimum 10.2m². Some councils require larger rooms.
• •Shared facilities: adequate kitchen and bathroom provision per number of occupants is a planning and licensing requirement
• •Parking: some boroughs require no net increase in on-street parking demand — this can be a challenge in CPZ areas

**Planning timescales**: 8–13 weeks for a standard householder/change of use application in London.

An HMO conversion triggers a broader and more demanding set of Building Regulations requirements than a standard residential refurbishment. The key requirements:

• **Part B — Fire Safety**:
• Fire safety is the most critical Building Regulations element in any HMO conversion. Requirements:
• •Fire detection and alarm system (Grade D1 or D2 minimum — interlinked mains-powered smoke alarms in all rooms, heat detectors in kitchen and garage)
• •Fire doors (FD30S — 30-minute fire-resistant with intumescent and smoke seals, and automatic self-closing device) on all habitable room doors, kitchen, staircase enclosure doors
• •Protected escape route: the staircase must be a protected route from the highest floor to the front door. All openings into the protected route must be via FD30S fire doors. All pipes and cables penetrating the fire compartment walls around the stair must be fire-stopped.
• •Emergency escape lighting: required on staircase and in corridors where natural light is not available in an emergency

• **Part E — Sound Insulation**:
• Sound insulation between bedrooms in an HMO must meet specific values (Dnt,w + Ctr ≥ 45dB for airborne sound; L'nT,w ≤ 62dB for impact sound). In an existing Victorian terrace with timber joist floors, achieving Part E requires:
• •Resilient bars and acoustic plasterboard on ceiling
• •Acoustic floor system (acoustic mat + floating floor above)
• •Party wall upgrade (dense mineral wool in stud partition between rooms)

• **Part F — Ventilation**:
• •Extractor fans in all bathrooms and kitchens meeting the minimum extract rates (30 l/s for kitchen, 15 l/s for bathroom)
• •Background ventilation (trickle vents in windows) in all habitable rooms

**Part L — Thermal Performance**: If the refurbishment involves replacing windows or reroofing, the new elements must meet current U-value requirements.

**Gas Safety**: gas installations must be inspected and certified. Annual Gas Safety Certificate required for any rental property.

Separate from planning and Building Regulations, most London HMOs require one or more licences from the local council.

• **Mandatory HMO Licence**: required for HMOs with 5 or more occupants across 3 or more storeys. The licence application requires:
• •Confirmation that the property meets the minimum room sizes (6.51m² single, 10.22m² double — the statutory minimums from the Housing Act 2004 and the Management of HMO Regulations 2006)
• •A floor plan and schedule of accommodation
• •Confirmation of fire safety measures (fire alarm system, fire doors, emergency lighting)
• •Confirmation that gas, electrical, and fire safety certificates are current
• •Management arrangements for the property
• •The applicant (or manager) must be a fit and proper person — no relevant criminal convictions etc.

**Additional Licensing**: many London boroughs (see planning section above) have additional licensing schemes covering smaller HMOs (3–4 occupants). The application requirements are similar to mandatory licensing.

**HMO licence cost in London**: typically £500–£1,500 per property depending on the council and number of occupants. Licences are typically valid for 5 years.

• **Annual obligations under an HMO licence**:
• •Annual gas safety check (GAS certificate)
• •5-yearly electrical installation inspection (EICR)
• •Annual fire alarm test and maintenance log
• •Emergency lighting check (6-monthly)
• •Maintenance of the common parts

**Penalties for unlicensed HMOs**: operating an unlicensed HMO carries a fine of up to £30,000 per property. Tenants can apply to a rent repayment tribunal to reclaim up to 12 months' rent. This is a significant financial risk for landlords who are unaware of or ignore licensing requirements.

HMO conversion costs depend on the number of rooms, the existing condition of the property, and the specification required to meet licensing and planning standards.

**Typical HMO conversion costs (London, 2026, excluding VAT)**:

| Property size | Rooms | Scope | Estimated cost | |---|---|---|---| | 3-bed terrace | 5 rooms | Light conversion (redecorate, fire doors, fire alarm) | £18,000–£35,000 | | 3-bed terrace | 5 rooms | Full conversion (rewire, re-plumb, replaster, fire doors, alarm, ensuite) | £60,000–£100,000 | | 4-bed semi | 6 rooms | Full conversion with en-suites | £90,000–£140,000 | | 5-bed house | 7 rooms | Full conversion with en-suites, sound insulation upgrade | £130,000–£200,000 |

• **Key cost elements in an HMO conversion**:
• •Fire doors (FD30S, supply and installation): £650–£1,200 per door
• •Fire alarm and detection system (interlinked, Grade D1): £3,500–£8,000 installed
• •Emergency lighting: £1,500–£4,000 installed
• •Sound insulation upgrade (acoustic floor and ceiling): £80–£160/m²
• •En-suite shower rooms (per room): £6,000–£15,000
• •Full rewire (HMO-specific, Part P compliant): £9,000–£16,000
• •Kitchen upgrade (shared HMO kitchen, larger than standard): £12,000–£25,000
• •Planning application: £258 fee + architect £2,500–£5,000
• •Structural engineer (if structural changes): £600–£2,000
• •HMO licence: £500–£1,500 (council fee)

**Note**: second-fix materials (tiles, sanitaryware, kitchen units) are client-supplied under rcbGroup's standard terms. This can significantly reduce the cost quoted above or require a separate allowance depending on the arrangement.