🏢 Flat Conversions: Planning Permission & Building Regulations

A clear, practical guide for UK projects

Converting a house into flats is perfectly achievable, but it’s one of the most regulated types of residential development. Two separate regimes apply:

• Planning Permission – concerned with use, appearance, impact on neighbours, parking, amenity, local policy
• Building Regulations – concerned with safety, structure, fire protection, sound insulation, drainage, ventilation, energy efficiency

You almost always need both.

1. 🧭 When Planning Permission Is Required

You will almost always need planning permission to convert a single dwelling into multiple flats because it is a material change of use (C3 → C3 multiple units).

Local authorities typically assess:

Key Planning Considerations

• Amenity standards
  • Minimum space standards (nationally described space standards, if adopted)
  • Natural light to all habitable rooms
  • Private outdoor space (sometimes required)
• Impact on neighbours
  • Noise, overlooking, loss of privacy
  • Over-intensification of use
• Parking & transport
  • Off‑street parking requirements
  • Cycle storage
  • EV charging (in some boroughs)
• Waste & recycling storage
  • Dedicated, accessible bin storage
• Design & external changes
  • New entrances, stair cores, dormers, rooflights, extensions
  • Conservation areas and listed buildings require extra scrutiny
• Housing mix policies Some councils restrict conversions to protect family housing stock.

When Planning Permission Might Not Be Needed

Very rare, but possible if:

• The building is already lawfully in multiple occupation
• You are converting between certain HMO categories (C4 ↔ Sui Generis)
• You have an existing certificate of lawful us

2. 🔥 Building Regulations for Flat Conversions

Even if planning permission isn’t required, building regulations approval is mandatory.

Critical Building Regs Areas

Fire Safety (Part B)

• 30–60 minute fire‑resistant compartmentation between flats
• Protected escape routes
• FD30S fire doors
• Mains‑linked smoke/heat alarms
• Fire separation to lofts, basements, stairwells
• Emergency lighting (in some cases)

Sound Insulation (Part E)

• Acoustic separation between units
• Pre‑completion sound testing unless using an approved Robust Detail

Structure (Part A)

• Load‑bearing walls removed? → Structural engineer required
• Floor strengthening for new layouts

Drainage & Sanitation (Part H)

• New bathrooms/kitchens need compliant drainage runs
• Ventilation of soil stacks

Ventilation (Part F)

• Extract fans in kitchens/bathrooms
• Background ventilation (trickle vents)

Energy Efficiency (Part L)

• Upgraded insulation
• SAP calculations for each new flat
• Efficient heating systems

Access (Part M)

• Reasonable provision for access to and within the building
• Requirements vary depending on storeys and entrances

Electrical Safety (Part P)

• All electrical work must be certified by a competent person

3. 📝 Other Requirements

Building Control Route

You can choose:

• Local Authority Building Control (LABC)
• Approved Inspector / Building Control Approver

Licensing

If the flats will be rented:

• HMO licensing may apply
• Selective licensing in some boroughs

Freeholder Consent

If leasehold, you may need:

• Freeholder consent
• Party Wall notices
• Updated leases