What does a wrong official floor area mean when selling?
The registered area is the basis for the listing, the price per square metre, and the buyer's comparison. If it is wrong, it is usually discovered late — and it is more expensive to correct mid-sale than before.
Short answer: A wrong registered floor area hits a sale in three places: pricing (price per square metre is worked out from the area), the listing (the sales particulars are usually built on the official record) and trust (a buyer who measures for themselves and finds something different starts doubting everything else in the listing). If there are unregistered changes to the property, an approval may also be missing. Fix it before the home goes up for sale — a correction has to be processed by an authority, and that takes time you won't have in the middle of a sale. Every country keeps this kind of record under a different name and with different rules for what counts — council records or the Land Registry in the UK, the county assessor in the US.
First: is the area actually wrong?
Most "wrong" areas aren't wrong. The property register usually measures externally — to the outside face of the external walls, with internal partition walls counted in — while a tape measure gives you the internal dimension, wall to wall. The difference is the walls themselves, typically 10-20%, and most pronounced in a small home with thick walls.
Work it out before you do anything else: the external walls take up roughly the wall thickness times the house's perimeter. A house measuring 8 × 12 m has a perimeter of 2 × (8 + 12) = 40 m; with 35 cm external walls that gives 40 × 0.35 = 14 m² — slightly on the high side, because the corners get counted twice, so call it a good 13. Partition walls add another 2-4 m² on top. Out of 96 m² measured externally, around 17% of the area disappears once you measure internally. If that accounts for the gap, there is nothing to fix.
If there is still 10-20 m² left over that the walls can't explain, something is unregistered — and that is relevant for the sale.
Where it hits in a sale
Pricing. The price per square metre in an area is worked out from the floor area. If the record understates it by 20 m², your home gets compared with smaller homes, and the asking price can end up set too low. If it overstates it by 20 m², the home looks cheaper per square metre than it is — and the buyer finds out at the first viewing, tape measure in hand.
The listing. It is usually built on the official record. If the agent is to write a different figure, there has to be a basis behind it — typically a survey from a licensed surveyor. Without that basis, the listing keeps quoting the wrong number.
The approval. Often the heaviest of the three. If an area isn't registered because there was never a building application — a garage turned into a room, a finished attic, an enclosed terrace — the question isn't just how many square metres there are, but whether they're legal. That question belongs with the authority, and it should be settled before the sale, not during it.
Trust. Hard to measure and easy to lose. A buyer who finds one thing that doesn't add up starts checking everything. Deals that fall apart often fall apart right there.
Why it has to be sorted before the listing goes live
A correction to a property record has to be processed by whichever authority maintains it. If the correction needs a surveyor's measurement or a building application, it takes longer — and you are not first in the queue just because you're in a hurry to sell.
If the problem instead surfaces when the buyer's advisor goes through the paperwork, you're under a time pressure you don't control. That is the situation where sellers accept a discount they shouldn't have had to give, just to keep the deal moving.
So: go through the property's official registration before you contact the agent. Read the field names, not just the numbers — living area, basement area, finished attic, conservatory, garage and carport are each their own field.
How to prepare as a seller
- Get hold of the property's registration and go through it field by field — including the heating system, number of bathrooms and toilets, outbuildings and garage. Those fields go out of date just as often as the area does.
- Measure the home room by room: length and width at floor level, in two places in each direction. Note alcoves and projections separately.
- Measure the external wall thickness at three window reveals — that is the piece that translates your internal measurement into the record's external one.
- Gather the documentation: old building permits, drawings, receipts from renovations. That is what the authority and the buyer will ask for.
- Call the authority and ask what is needed before you book a surveyor. Often less is required than you'd think.
- Tell the agent everything you know. A known discrepancy disclosed from the start is a completely different situation from the same discrepancy discovered by the buyer.
What specifically applies in your sale — disclosure duties, liability, the consequences of an error in the listing — are legal questions. Put those to your agent and your advisor, not to an article.
As a buyer: how to spot it early
Get hold of the property's official registration before you go to a viewing. Add the fields together one at a time, and see which combination lands on the listing's headline figure — that immediately reveals whether the basement or the conservatory is counted in "the 1,700 sq ft".
Measure two or three of the largest rooms at the viewing, and measure the external wall thickness at a window. You're not checking the whole house; you're checking the order of magnitude. If it doesn't line up with what the walls can explain, ask — and get the answer in writing.
A measured basis makes the conversation concrete
Whether you're selling or buying, the strongest thing you can have in hand is your own measured numbers and a drawing to point to.
HouseSense produces that: scan the home with the iPhone's LiDAR, or draw it on graph paper with your finger. You get a measured floor plan with area per room and in total, measured internally wall to wall, and you can send it on as a PDF. Walls that meet a neighbouring room become one shared wall, so two rooms never count the same square metres twice.
HouseSense doesn't decide whether the official record is correct — the authority that maintains it does that. But a measured internal area and a drawing make the difference between saying "I think there's more floor area" and being able to show where it is.
Three questions that settle most of it
- Can the walls explain the difference? Wall thickness times perimeter, plus 2-4 m² for partition walls. If they can, there's no case to answer.
- Have any changes been made that aren't registered? An extension, a finished attic, a converted garage, an enclosed terrace. Write them down with years, as best you can.
- Is there approval for the changes? Dig out building permits and old drawings. If there's nothing, ask the authority what is needed — before the listing goes live.
Those three questions take an afternoon to answer. The same question asked by a buyer's advisor two days before signing takes a good deal longer.