For homeowners, landlords and small developers
Converting a House into Flats in London: Planning, Rules and Process
Sviatoslav JerdetchiiCEO & Founder of Craftex. Updated , 5 min read
The short answer
Converting a house into flats in London always needs planning permission, and most boroughs only allow it for larger houses. Every new flat must also meet the space standards and Building Regulations.
- Check your borough's minimum size: 130 m² is a common threshold.
- Test every flat against the London Plan space standards before you design.
- Budget for fire separation and sound insulation between flats.
- Agree the 5% VAT rate and the CIL position before you sign a contract.
The first question isn't how to lay out the flats. It's whether your borough will let the house be split at all.
To convert a house into flats in London, you always need planning permission. Most boroughs only allow it for larger houses, and many want one family-sized flat kept. Every new flat must meet the space standards. The work also needs Building Regulations approval.
This guide takes you through each test in order. Own a house that could become flats? Book a site visit and we'll check it with you.
Planning permission to convert a house into flats is always needed
The law treats using one house as two or more homes as a material change of use. There are no permitted development rights for it. So a house conversion always needs a full planning application.
A listed building also needs listed building consent. Unconsented works to a listed building are a criminal offence.
Step 1: check your borough allows the conversion
Each borough sets its own rules in its local plan, mostly to protect family homes. Two examples show the pattern.
| Borough policy | Minimum size | Family unit | Other tests |
|---|---|---|---|
| Lambeth, Policy H6 | Homes under 130 m² as originally built are protected | A family-sized home at ground floor with garden access, where practicable | No parking permits for new units in a CPZ; cycle and bin storage |
| Brent, Policy BH11 | At least 130 sq m, or reasonably extendable to it | At least one 3-bedroom home, ideally with a garden | Site at PTAL 3 or above |
Other boroughs use similar tests with different numbers. Some limit how many conversions a street can have. Check the local plan, any supplementary guidance and any Article 4 direction. Look at recent decisions on similar houses nearby. If the policy is unclear, a pre-application enquiry is often worth it.
Step 2: test the flats against the space standards
Every new flat, including one made by conversion, must meet London Plan Policy D6. That means the Nationally Described Space Standard: minimum floor areas, bedroom sizes, built-in storage and a 2.5 m ceiling for most of the flat. Private outdoor space is expected where possible.
In a period house, this is where schemes fail. A tall ground floor and a low loft rarely give equal flats. Stairs, a new lobby and fire separation all take space. Our guide to nationally described space standards has the full table.
At 74 Allitsen Road in St John's Wood, we studied a vacant four-storey corner building of 458 m². Our team drew a schedule of accommodation for four design options. We tested each one against the London Plan space standards. The options ranged up to seven flats. Testing the numbers first tells you whether a scheme works.
We used Craftex for a shop-to-flat conversion in Chelsea — turning an old retail space into two rental units. Access wasn’t the easiest, but the guys handled it well, no drama. Quote was clear, no hidden extras, and they actually stuck to it, which is rare. Finish came out solid, exactly what we needed for rentals. Joe (PM) kept things ticking and communication was always on point. All in all, smooth job — would use them again for sure.👍
Step 3: heritage, neighbours and the outside
- Conservation area. New doors, front bins and bike stores, roof changes and rear extensions are judged against the area's character.
- Extensions. A loft or rear extension that makes the scheme work usually goes in the same application.
- Party walls. Work to shared walls or new foundations near neighbours brings in the Party Wall Act.
Step 4: Building Regulations for a house to flats conversion
Creating flats in a house is a material change of use under the Building Regulations too. These are the main requirements.
| Area | What it means in practice |
|---|---|
| Fire safety | Fire-resisting separation between flats and to the common stair, fire doors, a protected escape route, smoke alarms |
| Sound | Sound insulation in separating floors and walls, normally proven by testing before completion |
| Structure | New openings, steel beams and new loads checked by an engineer |
| Ventilation | Kitchens and bathrooms ventilated to current standards |
| Energy | Insulation and heating upgrades for the work done |
| Drainage and water | New soil stacks and supplies routed through the building |
| Services | Usually separate meters and heating for each flat |
Fire separation and sound insulation through an old timber floor drive cost most often. They also eat ceiling height. Survey before you design.
Step 5: the costs that are easy to miss
Community Infrastructure Levy. Any new home is potentially liable for the Mayor's and the borough's CIL. But floorspace in lawful use for six continuous months in the three years before permission can be deducted. That often brings a straight conversion down to little or nothing. A long-empty house can lose the deduction. See our guide to CIL and Section 106.
VAT. A conversion that changes the number of homes qualifies for the reduced 5% VAT rate on the building work. One house into three flats is a typical case. The contractor must apply it correctly, so agree it before the contract. The empty-homes route is covered in VAT on empty homes refurbishment.
Tenure. Selling flats usually means granting long leases and setting up a freehold or management company. Plan the service charge and insurance. If you'll keep and let them, check your borough's licensing rules and your lender's criteria for converted flats.
The conversion process, start to finish
- Feasibility. Survey, measured drawings, borough policy check, outline layouts, cost and value.
- Pre-application advice. Optional, but useful where policy is tight.
- Planning application. Drawings, design and access statement, heritage statement if needed, cycle and bin details.
- Technical design. Structure, fire strategy, acoustics, services and the Building Regulations application.
- Party wall notices. Served early enough not to hold up the start.
- Tender and contract. A lump-sum price on a full specification.
- Construction. Strip-out, structure, separation, services and fit-out.
- Testing and sign-off. Sound tests, completion certificate, fire and electrical certificates.
- Sale or letting. Leases, management and warranties.
Before you commit to a conversion
We take house and building conversions from feasibility and site appraisal through planning to construction. We also refurbish prime homes across London. Herbert Crescent in Knightsbridge was a 450 m² refurbishment over 32 weeks, with the neighbours protected throughout. For prime houses, see our home renovation and refurbishment service.
Own a house in London that could become flats? Book a site visit and we'll tell you how many homes it could take.
House to flats checklist
- Check the original floor area against the borough threshold.
- Read the borough's conversion policy and recent decisions on your street.
- Test the layouts against the London Plan space standards.
- Check listed status, conservation area and Article 4 directions.
- Survey floors and walls for fire and sound upgrades.
- Confirm the CIL in-use evidence and the 5% VAT position.
- Price the build on a full specification, not a rate per m².
