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Why is my flat smaller than the paperwork says?

Because the registered area of a flat is, as a rule, a gross area: walls and often a share of the stairwell and corridors count towards it. Your floor is always smaller.

The paperwork's area and the floor's area are two different figures

When you measure your flat with a tape measure, you measure internally: wall to wall, room by room. That is the floor — what you can stand on, lay parquet on, and put a bed in.

The area in the official building record, in the sales listing and in the lease is usually a gross area. It is larger because it counts things you cannot stand on:

• The exterior walls, or part of them.
• The internal partition walls inside the flat.
• For owner-occupied flats: often a share of the building's shared access areas — stairwell, lift, corridor.

That last item is the one people don't know about, and it is often the single biggest reason a flat is "missing" square metres. Exactly how access areas are allocated and registered is technical and varies from building to building — ask whoever manages the property if you want to know how it is done in yours.

The sums in a block of flats

A flat is registered at 84 m². You measure the rooms and add them up:

• Living room 26.4 m² · bedroom 13.8 m² · bedroom 10.2 m² · kitchen 9.6 m² · bathroom 5.1 m² · hallway 6.3 m²
• 71.4 m² of floor, total.

12.6 m² — 15 % — is "missing". Here is roughly where it goes:

• Exterior walls: an old block of flats often has 35–50 cm exterior walls. With two exterior walls of 9 m each, 45 cm thick: 2 × 9 × 0.45 ≈ 8.1 m² — but only the share that belongs to the flat counts. Reckon on a few square metres.
• Partition walls: 30 linear metres × 0.12 m ≈ 3.6 m².
• Share of stairwell and corridor: the rest.

The numbers won't land on the decimal, and they don't need to — the point is that 12–13 m² disappears into walls and shared areas, not into an error.

Blocks of flats lose more than houses

There are two reasons the difference is bigger in a flat than in a house.

The walls are thicker. A block of flats built before 1930 can have a ground-floor exterior wall of 45–60 cm. That eats square metres along the whole facade.

There are more walls per square metre. An 84 m² flat often has just as many rooms as a 120 m² house. More rooms means more partition walls, and every partition wall is square metres that count on paper but not underfoot.

Rule of thumb: walls cost roughly the thickness times the linear metres of wall. 30 metres of wall at 12 cm is 3.6 m². That sounds small, until you realise it is an entire child's bedroom.

How to find your own explanation

• Measure the thickness of the exterior wall at a window reveal: from the inner wall face to the outer. In old buildings it is often surprisingly thick.
• Measure room by room at the floor, in two places in each direction — walls in older buildings are rarely parallel. Add the areas together; that is your floor.
• Find out which field the figure sits in in the official building register. Living area, total area and share of shared area are not the same figure.
• Ask the building's management whether a share of the access areas is included in the flat's registered area, and how much. It is a normal question, and the answer is usually found in the building's own paperwork.

When is it worth pursuing?

If walls and a share of shared area can explain the difference, there is nothing to chase. That is simply how the system is put together, and it applies to every flat in the building the same way — including the ones you are comparing your price per square metre against.

If there are many square metres left over that neither walls nor shared area can explain — or if a room, a loft space or a cellar room is included in the figure without actually being part of the flat — then it is no longer a sum. Then it is a registration that needs checking with the authority that maintains the official building register — and with the building's management, if you own your flat.

If you are a tenant, and the area stated in the lease determines your rent, that question belongs with someone who advises on tenancy matters. It is not something a tape measure settles on its own.

The figure you actually need to use for something

Use the registered area when you talk to the outside world: price per square metre, insurance, listing, valuation. That is the shared yardstick.

Use your measured floor area when you are buying something. Order parquet for 84 m² because that is what the paperwork says, and you end up with 12 m² too much — which is expensive timber to have sitting in the hallway. The same goes for paint, underfloor heating, tiles and carpet.

And use the rooms' areas one by one when you ask for a contractor's quote. "The flat is 84 m²" is not a job anyone can price. "Living room 26.4 m², two bedrooms at 13.8 and 10.2 m² — all floors sanded" is.

How to get the floor area without a spreadsheet

HouseSense measures internally, wall to wall, and gives you the area per room and in total: scan the flat with your iPhone's LiDAR, or draw it on the screen's squared paper with your finger. Walls that meet each other become one shared wall, so two rooms never count the same square metres twice — and you get a measured floor plan you can send on as a PDF.

What the app gives you is the floor. What the paperwork gives you is the gross area. You need both, and they are not meant to be the same.