Check what the advertised extra space can actually do

Investigate Costa del Sol basements, annexes and extra bedrooms through plans, intended use, conversion records, condition, access and rental assumptions.

“Independent apartment”, “guest annex”, “converted basement” and “extra bedroom” can make a Costa del Sol property appear more flexible than its main floor plan suggests. The useful question is what the space actually is, what documents describe it and how it can be used. Furniture, a kitchen or a separate entrance do not settle those questions on their own.

This guide helps buyers investigate advertised extra rooms in Marbella villas, Mijas townhouses, Málaga apartments and inland properties. It supports the listing decoder and occupancy and change-of-use guide. The building photograph gives regional context and does not identify an annex or certify a use. Avoid counting uncertain space as essential accommodation before the relevant enquiries are resolved.

Write down the proposed use before inspecting

Explain what you want the space to do: occasional storage, a home office, a bedroom for family visits, a permanent bedroom, a separate dwelling or accommodation offered to paying guests. Those are different briefs. A room that suits luggage storage may not meet the requirements or practical needs of the use you intend. Tell the lawyer and technical adviser the full plan, including any proposed cooking or bathroom facilities.

Separate present use from future potential in your notes. If an advert says “could become an apartment”, record it as an unverified proposal rather than an included apartment. The renovation-project buying guide helps place feasibility before quotations and purchase assumptions. A seller's belief that a change is straightforward should become a question to investigate, not a conclusion in your comparison sheet.

Identify the exact space on records and plans

Ask the seller for available plans and relevant building, planning and title documents. Have the professionals connect them with the room you visited. Use clear labels such as “lower level, door beside garage” rather than a marketing name that may change between adverts. Request clarification where a drawn storage area is being described as a bedroom or an independent unit.

The Land Registry and Cadastre guide explains why different records serve different purposes. An area figure on one record is not a complete answer about authorised use, building condition or permission for a proposed division. Ask what remains missing, whether records disagree and what investigation is necessary. Keep the professional explanation with the supporting documents instead of retaining only a verbal summary.

Understand basement and semi-basement labels

“Sótano” and “semisótano” are useful starting terms, but inspect the actual relationship between the rooms, outside ground levels and entrances. A partly below-ground space can vary across the building. Note which walls or openings face a courtyard, garden or passage and which parts were inaccessible. Do not infer suitability from a label, photograph or the brightness of a staged room.

Ask the technical adviser to investigate the matters relevant to the intended use, including condition, moisture, ventilation, access and other applicable requirements. The official CTE health-protection documents are a reference for professional assessment, not a checklist that a buyer can use to certify a room. Requirements and their application need evaluating for the specific building and works.

Investigate conversion history and approvals

Ask what changed, when it changed and which project, permission and completion records are available. Establish whether the present layout differs from the records supplied. A conversion described as old or already in regular use still needs an investigation appropriate to the property. Do not accept a generic assurance that the passage of time resolves every planning and use question.

Andalucía's territorial and urban-planning legislation provides the regional framework. The actual position also depends on the property and applicable local planning. The permissions guide helps organise the questions for the municipality and advisers. Do not assume one application route or a particular outcome from a comparison with another house nearby.

Treat an independent entrance as one feature

A separate door can be convenient, but it does not by itself establish a separate legal dwelling or a right to let independently. Ask which title, access, utility and shared-building arrangements would apply to the proposed activity. Where a route crosses a garage, common area or another owner's land, request the supporting rights and practical access explanation.

Read the boundaries and easements guide with the actual route. For a villa advertised with a guest house, ask whether the annex belongs within the same transaction and what the relevant records say. For an apartment building, connect the enquiry with the community's documentation. A photograph of a private-looking entrance cannot replace that work.

Assess the complete daily route

Walk the route you would use with luggage, shopping or laundry, where access is permitted. Record steps, narrow turns, door operation and the relationship with the main accommodation. The accessible-home brief helps translate these observations into the requirements of the actual household. Avoid assuming that a lower-level room is accessible simply because it has a door to a garden.

Ask the appointed professional to consider safe use and relevant escape arrangements for the proposed occupation. Do not improvise conclusions from the number of visible doors or windows. If someone would sleep or work there regularly, include that use explicitly in the appointment. A casual viewing of the room as storage may not address the questions that matter to accommodation.

Keep moisture, drainage and services in the same brief

Ask about leaks, flooding, drainage changes, ventilation equipment and previous remedial work. Retain dates and records. Recent decoration can make history less visible, while dry weather can leave an important question unanswered. Use the damp-investigation guide to define the appointment and further evidence rather than assigning a cause to marks or smells.

Identify which water, drainage, hot-water, electrical and climate-control systems serve the space. A furnished kitchenette does not explain service capacity, installation condition or any approvals. Where systems are shared, clarify who maintains them and how problems are accessed. Budget for assessment and necessary work before treating the room as ready for your intended use.

Do not turn extra space into assumed rental income

An advert may suggest that an annex can “pay for the house”. Before using that claim, investigate the permitted use, appropriate rental framework, building arrangements, costs and actual demand evidence. Existing occupation or a past booking is not a complete finding about a buyer's future activity. Keep projected income out of the base affordability case until the material assumptions have been assessed.

The rental-projection guide and buy-to-let risk guide provide the broader analysis. Explain to advisers if separate letting is essential to your plan. If it cannot be established, compare the home on the use you can support rather than increasing the forecast to justify the asking price. Obtain advice on the actual arrangement before commitment.

Use an evidence-led comparison example

Consider a fictional Mijas townhouse marketed as three bedrooms plus a guest apartment. The main accommodation has three bedrooms; the lower level contains a sofa bed and shower, but the seller has not supplied documents explaining its use. Record the lower level separately as an unresolved feature. Request the records, commission the appropriate assessment and avoid comparing it directly with a verified four-bedroom brief.

Use the property-comparison workspace to retain both the attraction and the uncertainty. Ask the lawyer how any important outstanding matter should be reflected in the proposed transaction. A reduction in price does not itself supply missing approvals, resolve condition or make a proposed use possible. The relevant question is whether the home works for you with the evidence actually available.

Keep a clear room-by-room decision record

For each extra space, retain the advert wording, observed layout, proposed use, documents supplied, inspection scope and unanswered questions. Download the evidence sheet and identify the person responsible for each follow-up. Research checked on 11 November 2026. This preparation supports a property-specific investigation; it does not certify a room, promise a conversion outcome or replace planning and technical advice.