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Flat Conversions
🏢 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
🧭 Do I Need Planning Permission?
A simple decision tree for flat conversions
1️⃣ Are you changing the number of dwellings?
- Yes — turning 1 house into 2+ flats → Planning permission required.
- No — number of units stays the same → Go to Step 2.
2️⃣ Are you changing the building’s use class?
Examples:
- C3 house → C3 flats
- C3 house → C4 small HMO
- C3 house → Sui Generis large HMO
- Yes → Planning permission required (unless you already have a lawful use certificate).
- No → Go to Step 3.
3️⃣ Are you making external alterations?
Examples:
- New doors or entrances
- Dormers, rooflights, extensions
- Altering the façade
- Converting a garage or loft with visible changes
- Yes → Planning permission required (or householder planning permission).
- No → Go to Step 4.
4️⃣ Is the property in a protected area?
- Conservation area
- Article 4 direction
- Listed building
- National park / AONB
- Yes → Planning permission almost certainly required.
- No → Go to Step 5.
5️⃣ Are you creating new self‑contained units with their own:
- Kitchen
- Bathroom
- Independent access
- Separate utilities
- Yes → Planning permission required (material change of use).
- No → Go to Step 6.
6️⃣ Are you only altering internal layouts?
Examples:
- Moving walls
- Reconfiguring rooms
- Adding ensuites
- Upgrading insulation
- Yes → Planning permission NOT required, but Building Regulations approval IS required.
- No → Go to Step 7.
7️⃣ Are you converting between HMO types?
- C3 → C4 (small HMO)
- C4 → C3
- C4 → Sui Generis (large HMO)
- Yes → Depends on your council. Many require planning permission due to Article 4.
- No → Go to Step 8.
8️⃣ Are you unsure or the situation is unusual?
Examples:
- Mixed‑use buildings
- Commercial → residential
- Outbuildings
- Basement conversions
- Yes → You should request pre‑application advice or a Lawful Development Certificate.
- No → You likely do not need planning permission.
⭐ Final Summary
If you are creating new flats, you need planning permission. If you are only changing internal layouts, you don’t — but Building Regulations still apply.
We have extensive experience, with successful planning and building regulations applications, for flat conversions, get in touch today!