Nationally Described Space Standards for Flats: The London Rules
The Nationally Described Space Standard (NDSS) sets the minimum internal floor area of a new home by its number of bedrooms, bedspaces and storeys: 37 to 39 m² for a one-person studio, 50 m² for a one-bedroom two-person flat, 70 m² for a two-bedroom four-person flat. It also sets minimum bedroom sizes, built-in storage and ceiling heights.
Nationally the standard is optional and only applies where a local plan adopts it. In London it applies to every new home through the London Plan, with a higher ceiling height of 2.5 metres. And homes created under permitted development, such as office-to-residential conversions under Class MA, must meet it anywhere in England.
Minimum floor areas for flats
These are the NDSS minimum gross internal areas (GIA), the same figures as London Plan Table 3.1. Single-storey flats use the first column; duplexes and maisonettes use the second.
| Bedrooms | Bedspaces (people) | 1-storey flat (m²) | 2-storey dwelling (m²) | Built-in storage (m²) |
|---|---|---|---|---|
| Studio / 1 bed | 1p | 39 (37 with a shower room instead of a bathroom) | N/A | 1.0 |
| 1 bed | 2p | 50 | 58 | 1.5 |
| 2 bed | 3p | 61 | 70 | 2.0 |
| 2 bed | 4p | 70 | 79 | 2.0 |
| 3 bed | 4p | 74 | 84 | 2.5 |
| 3 bed | 5p | 86 | 93 | 2.5 |
| 3 bed | 6p | 95 | 102 | 2.5 |
| 4 bed | 5p | 90 | 97 | 3.0 |
| 4 bed | 6p | 99 | 106 | 3.0 |
Larger homes (4 bed 7–8 person, 5 and 6 bed) and three-storey houses have their own figures in the standard.
Bedspaces drive the number, not just bedrooms. A two-bedroom flat with one double and one single room is a 2b3p (61 m²). Make the second room a double and it becomes a 2b4p (70 m²). That 9 m² difference, repeated across a building, changes the unit count.
The rules behind the numbers
The floor area is only the first test. The standard also requires:
| Element | Requirement |
|---|---|
| Single bedroom | At least 7.5 m² and at least 2.15 m wide |
| Double or twin bedroom | At least 11.5 m² |
| Bedroom widths | One double (or twin) at least 2.75 m wide; every other double at least 2.55 m wide |
| Built-in storage | As in the table, included in the GIA (with an allowance of 0.5 m² for fixed services such as a hot water cylinder) |
| Low headroom | Floor with headroom under 1.5 m isn't counted in the GIA, unless it's used only for storage |
| Storage under eaves | Storage with headroom of 0.9–1.5 m counts at 50% of its area; below 0.9 m it doesn't count |
| Built-in wardrobes | Count towards GIA and bedroom area, but mustn't reduce the room below its minimum width. Wardrobe area beyond 0.72 m² in a double (0.36 m² in a single) counts towards built-in storage |
| Ceiling height (national) | At least 2.3 m for at least 75% of the GIA |
| Ceiling height (London) | At least 2.5 m for at least 75% of the GIA |
GIA is measured to the internal faces of the walls around the dwelling. It includes partitions, structure, cupboards, ducts, stairs and voids above stairs.
What London adds
London Plan Policy D6 applies the space standard to all tenures and adds:
- 2.5 m minimum floor-to-ceiling height for at least 75% of each home's GIA.
- Private outdoor space of at least 5 m² for a one or two-person home, plus 1 m² for each extra occupant, with a minimum depth and width of 1.5 m. This doesn't count towards the GIA.
- Dual aspect homes to be maximised, and single-aspect homes only where they are shown to be the better option.
- Accessible housing under Policy D7: at least 10% of new-build homes to wheelchair user standard M4(3), and the rest to accessible and adaptable standard M4(2).
In March 2026 the government and the Mayor withdrew two parts of the GLA's housing design guidance as part of the emergency measures for London housebuilding: the guidance favouring dual-aspect homes and the limit on the number of homes around each core. Policy D6 itself, including the space standards, still applies.
London Plan Table 3.1 also makes clear that "new dwelling" includes conversions and changes of use, not just new build.
Permitted development: NDSS applies everywhere
Since April 2021, any new home created through permitted development in England must meet the NDSS. That includes office-to-residential conversions under the Class MA prior approval route, which is why so many early prior approval schemes that relied on very small flats are no longer possible. Every habitable room must also have adequate natural light, which the council must assess. Our permitted development and prior approval team checks both before a scheme is drawn.
Where schemes fail the standard
From the builder's side of the table, these are the places where layouts that look fine at planning stage fall short:
- The second bedroom width. A double bedroom that's 2.45 m wide is a single room in the standard's eyes, and the flat drops a bedspace.
- Storage forgotten or double-counted. Storage has to be shown and dimensioned. Space taken by a cylinder or plant needs the 0.5 m² allowance, not the whole cupboard.
- Ceiling heights in conversions. An office floor with a slab-to-slab height that suited a raised floor and a suspended ceiling can struggle to give 2.5 m once acoustic floors, services and fire separation go in. Measure it before you count homes.
- Roof spaces and mansards. Area under 1.5 m headroom doesn't count. A new top floor needs the headroom drawn early, especially in a conservation area where the roof profile is fixed.
- Columns and risers. Structure and service risers sit inside the GIA, but they also eat bedroom widths and kitchen runs. A layout that works on paper can fail once the real structural grid is overlaid.
- Outdoor space on conversions. Adding balconies to an existing façade may need planning permission and structural work. Where it isn't possible, agree the approach with the council before the layout is fixed.
How space standards decide the scheme
The space standard is often what decides how many homes a building can hold. It's a design input, not a box to tick at the end.
At 74 Allitsen Road in St John's Wood, a vacant four-storey corner building with an existing GIA of 458 m², our team prepared a schedule of accommodation for each of four design options and tested each against London Plan space standards. The result ranged from four apartments up to seven, with the difference coming from the basement and the roof. Historic floor-to-floor heights, blocked openings and a restrictive basement all shaped what was possible.
That's the order we recommend for any conversion or new build:
- Survey the building, including floor-to-ceiling heights and the structural grid.
- Fix the unit mix by bedspaces, not just bedrooms.
- Test every layout against the standard, room by room.
- Only then price it and run the appraisal.
A development feasibility and site appraisal does exactly that before the design is committed. For buildings changing use, see our commercial to residential conversion service and our guide to Class E and what it covers. If you're adding floors, our airspace and upward extension team works to the same standards. And rented schemes are no different: see our build to rent London guide.
Want to know how many homes your building can really hold? Send us the address. We'll look at the floor plates, the heights and the planning route.
