Section 257 HMO in Camden: Converted Flats and Block Licensing

Section 257 of the Housing Act 2004 creates a separate category of HMO that applies to entire buildings, not individual flats — and in Camden, the threshold for catching these buildings is lower than the national default. If you own or manage a converted block of flats, this is the licensing category that trips people up most often.

What Makes a Building a Section 257 HMO

A section 257 HMO is a building (or part of a building) that has been converted into self-contained flats where two conditions are met:

1. The conversion didn't comply with the Building Regulations 1991 (or whatever regulations were in force at the time of conversion) and still doesn't comply
2. Fewer than a certain proportion of the flats are owner-occupied

The first condition targets older conversions — typically Victorian and Edwardian houses divided into flats before modern building standards applied. If the conversion was done properly under the regulations in force at the time and still meets those standards, section 257 doesn't apply.

The second condition is where Camden differs from the national default.

Camden's 50% Threshold vs the National Rule

The national rule under the Housing Act 2004 uses a two-thirds threshold: a converted building is a section 257 HMO if fewer than two-thirds of the flats are owner-occupied. Camden's Additional HMO Licensing Designation 2025 sets a lower threshold — fewer than half (50%) of the flats need to be owner-occupied for the building to fall within the scheme.

In practice:

• A block of four flats where one is owner-occupied and three are rented: 25% owner-occupied — below Camden's 50% threshold
• A block of six flats where two are owner-occupied and four are rented: 33% owner-occupied — clearly caught
• A block of three flats where two are owner-occupied: 67% — above the threshold, not caught

The owner-occupier test counts flats where the leaseholder lives in the flat as their own home. Flats held by buy-to-let investors or rented out by their owners count as non-owner-occupied even if the investor is also a leaseholder in the block.

Who Holds the Section 257 Licence?

Here's the key difference from standard HMO licensing: the licence for a section 257 building is held by the freeholder or head leaseholder who controls the building's common parts — not by the individual flat landlords.

The licence covers the common structure: hallways, staircases, shared entrance, shared services. Individual flat landlords don't need a separate section 257 licence for their own flats.

However, if a flat within a section 257 building is independently let to three or more unrelated occupants sharing amenities, that individual flat also needs a separate section 254 HMO licence for itself. The two licence types can apply simultaneously — one for the building, one for the flat.

When Section 257 Doesn't Apply

The building regulations test matters. If the original conversion work was done to the standard required at the time and continues to meet it, section 257 doesn't bite — even if the building is 100% rented. Many post-1991 conversions that went through proper building control are exempt.

Purpose-built blocks of flats (designed from the start as flats, never converted from a house) are also outside section 257. This section targets conversions specifically.

What Freeholders and Head Lessees Should Do

If you're the freeholder of a converted block in Camden:

1. Check when the conversion was done and whether it went through building control at the time
2. Count how many flats in the block are owner-occupied versus rented
3. If the building was converted before 1991 building regulations, the conversion doesn't comply, and fewer than half the flats are owner-occupied — you almost certainly need a section 257 licence
4. The application goes through the same Camden online portal and costs the same as a standard HMO application (£1,570)

The Camden Landlord Licensing Guide includes a section 257 owner-occupier audit worksheet for working through the calculation and determining whether your block is caught.

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