Why do property documents show different area measurements?

Almost every week someone brings us three documents for the same apartment showing three different areas, and the same question: which one is true? The answer starts by taking the problem apart. The documents do not contradict each other because one of them lies; they differ because each was created to measure something distinct, under its own rules.

The areas that appear in the documents

Gross private area. The surface for the exclusive use of the unit, measured to the outer face of its enclosing walls and including half the thickness of walls shared with neighbouring units. This is the area used in valuation and in most market comparisons.

Gross dependent area. Ancillary spaces accessed from the unit or the building: garage, covered parking space, storage room, attic or usable basement. They are not worth the same per square metre as private area, so they should never be added to it without weighting.

Usable area. The habitable interior, measured without walls. It is always smaller than the gross private area and matches what you actually walk on. Listings usually quote gross private area; buyers mentally compare usable area. Half the disappointment on viewings starts here.

Construction area. A planning concept, used in permitting and in density calculations. It includes every floor and, depending on the municipal regulation, balconies, porches and technical areas. It measures whether the building fits what the plan allows, not what a unit is worth.

Plot area and footprint. For houses and land, plot area comes from the registry description and the tax record; the footprint is the projection of the building on the ground. Two plots of identical size can carry very different development capacity.

Where the discrepancies come from

In practice, differences almost always come from the same five causes:

1. Age of the tax record. Many records were filled in decades ago, under earlier measuring conventions, and were never updated.
2. Undeclared works. An enclosed balcony, a converted attic or a basement turned into storage change the real area without changing the paperwork.
3. Different measuring convention. The drawings measure to wall centrelines, the tax record to the outer face, the agent measures whatever a tape can reach.
4. Registry transcription. The land registry certificate repeats what was reported when the entry was made, including any errors present at the time.
5. Improper additions. Garage and storage added to private area produce a bigger number that is useless for comparison.

Which area does the valuer use

A defensible report does not pick the most convenient area: it measures and discloses. We measure the property on site, compare it with the drawings and the documents, and state the area used in the calculation together with its source. Where a material discrepancy exists, it is recorded in the report as a qualification, with an estimate of its impact on value.

This has practical consequences. An 8 % difference in the private area of a two-bedroom flat in Funchal can mean tens of thousands of euros in the bank valuation, which translates directly into the equity the buyer must put up.

When the documented area is larger than the real one, the buyer carries the risk. When it is smaller, the seller does, selling cheaply what they actually own. In both cases, measuring settles more than arguing.

How to correct a wrong area

• If the error is in the tax record: file an amendment declaration (IMI Model 1) with drawings and a descriptive report supporting the correct area.
• If the error is in the registry: request rectification of the property description, usually supported by a technical document evidencing the new measurement.
• If the difference results from building works: deal with the legality of the works first, the area second. Correcting the number without correcting the planning status merely documents the irregularity.
• If the difference is one of convention: there is nothing to correct, only something to explain. A clear technical note in the file stops the same issue from halting the mortgage three weeks later.

Check this before you sign

• Does the tax record area match the land registry?
• Does the listing add garage and storage to the living area?
• Do approved drawings exist in the municipal file, and do they match what you see on site?
• Have there been alterations to the unit that appear in no document?
• Does the bank valuation state which area it used?

If you answer "I do not know" to two of these, it is worth measuring before signing. A survey costs a fraction of renegotiating after completion.