The short answer
An undocumented improvement is one that exists in the property but is not reflected in the Land Registry entry, the cadastral record, or both. That is a documentation gap, and it is common along Costa Blanca South. The sale risk lies almost entirely in discovering it late: identified before launch, it is a planning item; identified after a buyer has committed, it becomes a renegotiation.
Physical property vs official records
Three descriptions of the same house have to be told apart:
- What exists — the building as it stands today.
- The Land Registry (Registro de la Propiedad) — the legal description of what you own, shown on the nota simple. This is what a buyer's lawyer relies on and what a lender lends against.
- The cadastre (Catastro) — the tax and mapping record: built area, use, plan. It drives IBI and appears in the sale file.
The three can disagree in either direction, and a mismatch between the registry and the cadastre is not the same problem as building without a licence. Establish which mismatch you have before deciding what to do about it.
What we see most often locally
- A pool added years after purchase and never declared.
- A glazed or roofed terrace (cerramiento) turning outdoor space into living space.
- An underbuild or basement converted into bedrooms, a games room or a summer kitchen.
- An extra bedroom or bathroom built into a solarium, garage or porch.
- A ground-floor extension into the garden on a detached villa or quad.
- Storage buildings, casitas, outdoor kitchens and pergolas on villa plots.
Many of these date back to a previous owner. That does not remove the issue, but it does mean the documentation trail is worth looking for before assuming there is none — licences, architect certificates and invoices often exist in an old file.
Why a discrepancy can affect the sale
Three separate pressure points, and they behave differently:
- The buyer's lawyer. Their job is to confirm that what the buyer pays for matches what is registered. Undeclared built area produces a query, and an unanswered query becomes a delay or a price reduction.
- The bank valuation. A valuer generally values documented area. Undeclared space can be excluded or the report issued with conditions, reducing the loan available to a financed buyer.
- The notary and completion. Where the description in the deed and the reality differ materially, the parties may need to regularise or expressly address it before signing.
Cash buyers who understand the local market often accept a documented, disclosed discrepancy without much drama. Financed buyers are where it bites hardest.
How to check — in order
- Request a current nota simple and read the built area and the described elements, not just the ownership section.
- Pull the cadastral record including the graphic plan, and compare its footprint and built area to the property as it stands.
- Gather what you hold: purchase deed, licences, architect certificates, works invoices, community consents.
- List every difference you find, with an approximate date for each piece of work.
- Take that list to an architect or technical architect for an assessment, and to your lawyer for the legal reading.
Where an architect comes in
An architect measures and certifies what actually exists, and can advise whether the works can be documented. The usual mechanism where it is available is a declaración de obra nueva — a declaration of the new construction at the notary, supported by a technical certificate and, depending on the situation, evidence of the age of the works — followed by updating the registry and the cadastre. Whether that route is open in your case depends on facts an architect has to verify on site.
Can it be regularised?
Sometimes, and it genuinely depends. The main variables are the age of the works, the classification and planning status of the plot (urban, rural, protected), the municipality's own rules and criteria, and whether any enforcement file exists. Outcomes range from a straightforward declaration and cadastral update, through a regularisation process with the town hall, to situations where the honest answer is that the works cannot be documented and the property is sold and priced as it is, with full disclosure.
We will not tell you every alteration is illegal, and nobody should tell you every issue can be legalised. Both claims are wrong often enough to be worth ignoring.
Before you market the property
- Know the registered and cadastral built area, and be able to state it accurately in the listing.
- Decide, with advice, whether you regularise before launch or sell as-is with disclosure.
- Have the file ready — nota simple, cadastral plan, licences, certificates.
- Brief your agent honestly, so the discrepancy is handled at enquiry stage rather than at the notary.
- Price for the buyer pool you are actually addressing: cash or financed.
A disclosed and evidenced discrepancy costs you far less than one that surfaces after an offer. Also note that if the registered area changes, IBI and some cost calculations can change with it — worth modelling before you commit to a route.
Where a valuation fits
If your property has documentation discrepancies, the right selling strategy depends on the specific property and situation. Ask us about preparing your property for sale — and start with a valuation that reflects both the documented and the physical property.
This guide is general information for sellers, not legal or technical advice. Planning and registry treatment varies by municipality and by property.
