Declare an additional dwelling in Catastro (registration/modification with Modelo 900D)

What you need to have at hand

1. Cl@ve, certificado digital o DNIe that works. Without it you can’t sign.
2. Referencia catastral of the original property (20 characters). You’ll find it on the IBI or at sedecatastro.
3. A computer with Chrome/Firefox. The Sede del Catastro is picky.
4. Time to upload PDFs without rush (30–45 min if you have everything ready).

Documentation

• DNI/NIE del titular and, if a third party acts, autorización de representación.
• Escritura or Nota Simple recent from the Registro.
• Licencia de obra or declaración responsable admitted by your ayuntamiento.
• Certificado final de obra signed by the technician. If you have licencia de primera ocupación, upload it too.
• Planos/croquis acotados with surfaces and layout of the new dwelling. Better a single clear PDF.
• Fotos that show before/after or the new unit.

Step by step

1. Go to https://www.sedecatastro.gob.es > Trámites and log in with Cl@ve or certificado.
2. Choose Declaraciones catastrales and open the Modelo 900D (alterations: obra nueva, ampliación, división/segregación).
3. Enter referencia catastral, fecha de fin de obra and the type of alteration (new dwelling/independent unit, or extension that creates another). Add titulares if ownership changes.
4. Fill in surfaces, uses and annexes (storage rooms, garages) linked to the new dwelling.
5. Attach licencia/declaración responsable, certificado final, planos and photos in PDF. Name files clearly and check they fit Sede limits.
6. Review and sign the submission. Download the justificante with CSV and save the expediente number.
7. Watch Mis expedientes for any requerimiento de subsanación. If they ask for something, upload it online within the deadline (don’t leave it to the last day).
8. When they resolve, go to the consulta descriptiva y gráfica and download the updated certification. Check surfaces and, if applicable, the new referencia.

Time-savers

• Combine plans and photos into one PDF each (plans in one, photos in another). You avoid upload errors.
• If you don’t have a Nota Simple, order it online first. It saves doubts about the titulares.
• If the process is for a division into two dwellings, coordinate with Notaría/Registro for the división horizontal. Catastro reflects it, but the formal paperwork goes there.
• If you’re missing a document, submit and don’t miss the 2 months deadline. Then respond to the requerimiento.

Typical mistakes that will mess up the process

• Not putting the real fecha de fin de obra: it won’t match the licence and they’ll require clarification.
• Uploading blurry documents or splitting one doc into lots of tiny PDFs: you’ll get a subsanación.
• Confusing Catastro with Registro: Catastro recording does not create new property rights without división horizontal.
• Using a referencia catastral that’s not the affected one: immediate rejection.
• Missing the 2 months deadline: possible fine and IBI retroactivo up to 4 years.
• Trying to sign from a phone: it often fails. Better use a computer and a compatible browser.