For developers and landlords

House to Flats
Conversion

Converting a house into flats is one of the most common small development projects in London and one of the most frequently refused. The number of units a house will take is almost never the number the floor area suggests, because amenity, refuse, cycle storage and sound separation all take space before you draw a single flat.

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Period house suitable for conversion into flats

The planning position

Always a full application, never permitted development

Subdividing a single dwelling into flats is a material change of use from Class C3 to multiple C3 units. There is no permitted development route for it. A full planning application is always required, and it is assessed on the full planning merits rather than a limited scope.

That matters because it means design, amenity, parking, refuse and neighbour impact are all in play, not just the change of use itself. Many boroughs also have policies resisting the loss of family sized housing, which can weigh against converting a large house into small units regardless of how well designed the scheme is.

The local plan position on unit mix is one of the first things to check, and it varies significantly between boroughs.

What we do

Establishing realistic unit yield first

The question every client asks is how many flats they will get. We answer it with a test layout rather than a rule of thumb, because the constraints that reduce yield are physical and specific to the building.

Once the yield is established and stands up against local policy, the planning application and the technical package follow.

  • Unit yield assessment against local policy and space standards
  • Test layouts before you commit to a purchase
  • Amenity space, refuse and cycle storage strategy
  • Sound separation and fire strategy design
  • Full planning application and supporting statements
  • Building regulations and technical design
  • Construction delivery under one contract

Before you bid

Check the site constraints first

Enter a site postcode and we check it against the national planning dataset for conservation areas, Article 4 directions, listed status, green belt and flood risk. Free, and it takes under a minute.

Check a site

What reduces the yield

Where the space actually goes

Space standards. Most authorities apply the nationally described space standards, which set minimum floor areas by bedroom and occupancy count along with minimum bedroom sizes and storage. A studio and a one bedroom flat have different floors, and undersized units get refused.

Amenity space. Ground floor units are usually expected to have private outdoor space, and upper units may need shared provision. That takes garden, which reduces what is available for anything else.

Refuse and cycle storage. Both need dedicated, accessible, weatherproof provision. On a narrow terrace with no side access this is a genuine constraint and it frequently forces a unit out of the scheme.

Circulation. A common stair and entrance hall eats floor area on every storey it passes through, and it has to satisfy means of escape.

Fire and sound

The technical requirements that shape the plan

Separating floors and walls between flats must achieve the sound insulation performance required by building regulations, and in an existing building with timber floors that usually means a build-up which raises floor levels or lowers ceilings. On a Victorian house with limited headroom that can be the difference between a compliant flat and an unusable one.

Fire strategy shapes the plan more than anything else. Protected escape routes, compartmentation between units and the position of the common stair all constrain where walls can go. Designing the layout first and resolving fire afterwards is how conversions end up needing redesign.

We design both alongside the layout rather than after it.

Article 4 and HMOs

A common point of confusion

Converting a house into self contained flats is not the same as converting it into a house in multiple occupation. They are different use classes with different requirements, and the Article 4 directions that many boroughs have made apply to HMO conversion, not to flat conversion.

If your intention is a shared house rather than self contained units, the route and the constraints are different. Our site constraints checker flags Article 4 directions on any address free, and we will tell you which regime you are actually in.

Working with us

Test the yield before you buy

A site appraisal from £1,000 gives you a test layout, a realistic unit count and the local policy position on unit mix, before you commit to a purchase. On conversions that number drives the whole appraisal, so getting it right at bid stage matters more than almost anything else.

If it proceeds we take it through planning, technical design and construction under a single contract.

Site Feasibility Appraisal

Know whether the site works, from £1,000

Unit capacity, planning strategy, constraint mitigation and an indicative programme to determination. Delivered in 10 working days. The fee is credited against our fees if you appoint us for the application.

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Common Questions

House to flats conversion - answered

Do I need planning permission to convert a house into flats? +
Yes, always. Subdividing a single dwelling into self contained flats is a material change of use and there is no permitted development route for it. A full planning application is required and it is assessed on the full planning merits, meaning design, amenity, refuse, parking and neighbour impact are all in scope.
How many flats will my house convert into? +
Fewer than the floor area suggests. Space standards set minimum unit sizes, amenity space takes garden, refuse and cycle storage need dedicated provision, and a common stair consumes floor area on every storey. The only reliable answer comes from a test layout, which is what a site appraisal provides.
Will the council object to losing a family home? +
Possibly. Many boroughs have local plan policies resisting the loss of family sized housing, and those can weigh against converting a large house into smaller units regardless of design quality. The policy position varies significantly between boroughs and it is one of the first things to check.
What are the space standards? +
Most authorities apply the nationally described space standards, which set minimum internal floor areas according to the number of bedrooms and occupants, along with minimum bedroom sizes and built-in storage. Units that fall below them are routinely refused, so they set a hard floor on how many flats a building can take.
Is a flat conversion the same as an HMO conversion? +
No. Self contained flats and a house in multiple occupation are different use classes with different requirements. Importantly, the Article 4 directions that many boroughs have made apply to HMO conversion, not to flat conversion, so the constraints are not the same. It is worth being clear which one you are actually proposing.
What sound insulation is required between flats? +
Separating floors and walls must meet the performance set out in building regulations. In an existing building with timber floors that usually requires a build-up which either raises floor levels or lowers ceilings. On a Victorian property with limited headroom this can determine whether a flat is viable at all.
Do the flats need outdoor space? +
Usually. Ground floor units are typically expected to have private amenity space and upper units may require shared provision. Requirements vary by borough but they consistently reduce what is available for the rest of the scheme, which is why they need factoring in at appraisal stage rather than at design stage.

For developers and landlords

Considering a conversion?

Send us the address and what you are hoping to achieve. We will tell you what the building will realistically take and what the local policy position looks like.

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