A converted area is not automatically habitable

In a house, the quality of the conversion can easily give the impression that a new habitable room has been created. A tiled and heated basement with a shower room may look like a genuine suite. An insulated attic with a bed and storage may appear to provide an additional bedroom.

However, appearance and everyday use are not sufficient. To be recognised as a room intended for people to occupy, an area must meet a range of technical and administrative criteria. Ceiling height, natural light, ventilation, humidity, safety and the authorised use of the room may all be examined.

It is therefore important to distinguish between three different concepts:

These three concepts may coincide, but this is not always the case.

Why does this distinction matter when selling?

When a property is offered for sale, buyers generally compare its living area, number of bedrooms, condition, location and features. A well-converted ancillary area can be an advantage, but it will not necessarily be perceived or valued in the same way as conventional living space.

A basement converted into a leisure room can make a house more attractive. It can give a household additional space and enable a wide range of uses. However, this does not mean that the full cost of the conversion will be recovered in the sale price.

Difficulties can arise when an owner adds together all converted areas and presents the total as living space. If the authorised plans, technical characteristics or designated use of the rooms do not support that description, the discrepancy may become an issue during the sale.

Ceiling height: 2 metres is not always sufficient

Ceiling height is one of the most commonly misunderstood criteria.

Under the method presented by Guichet.lu on the basis of the Luxembourg standard for measuring residential property, parts of a room with a ceiling height of less than 2 metres are not included in the living area. Basements are also listed among the areas that are excluded.

However, the 2-metre threshold is a measurement rule. It does not mean that a room automatically becomes habitable as soon as it reaches this height.

Luxembourg’s model building regulations propose a minimum clear ceiling height of 2.55 metres for rooms intended for prolonged occupation. They also contain specific provisions for mezzanines and attics.

Separate rules applying to dwellings and rooms rented or otherwise made available for residential purposes set a minimum height of 2.20 metres, with specific provisions for attic accommodation.

These figures are not necessarily contradictory. They answer different questions and do not all have the same scope. Owners and buyers should therefore avoid relying on a single figure and instead examine the property’s specific situation and the applicable municipal regulations.

Natural light, windows and ventilation

A room intended for regular occupation must provide satisfactory natural light and air renewal.

The model building regulations provide that rooms intended for prolonged occupation should receive direct natural light and a direct supply of fresh air. They also propose that the total area of the openings should represent at least one eighth of the net floor area.

The rules applying to rented dwellings and rooms require bedrooms and living rooms to have a window providing a direct view outside. Minimum window dimensions are also specified for rooms covered by those rules.

Basement windows are often small, positioned high on the wall or located in a light well. Even where the room is heated and attractively decorated, the natural light and ventilation may therefore remain insufficient for the intended use.

Humidity and sanitary conditions: essential considerations below ground level

A basement is more exposed to water infiltration, rising damp, thermal bridges and condensation. These issues are not always visible during a brief viewing, particularly after a recent renovation.

The rules applying to rented dwellings and rooms require protection against humidity, cold, heat and draughts. They also address contamination and concentrations of microorganisms that may harm the health of occupants.

Before converting or purchasing a basement area, it is therefore advisable to examine:

Can a basement nevertheless become habitable?

It would be too categorical to state that a room below ground level can never be habitable.

The model building regulations provide that rooms intended for prolonged occupation are generally prohibited in basements unless they comply with the requirements applying to such rooms, subject to an exception concerning certain direct views.

In practice, feasibility therefore depends on the configuration of the basement, its height, openings, ventilation, sanitary conditions and safety, as well as compliance with the municipal rules and the permits granted.

Installing flooring, heating, a kitchen or a shower room is not sufficient to officially change the authorised use of a basement.

Does a bedroom have to measure at least 9 m²?

The 9 m² rule is often quoted as though it defined every bedroom in Luxembourg. The position is more nuanced.

The legislation applying to dwellings and rooms rented or otherwise made available for residential purposes provides for a minimum area of 9 m² per occupant for rooms falling within its definition. In this context, a “room” includes accommodation where the kitchen, living room or bathroom is located outside the room and intended for shared use.

This rule does not mean that every 9 m² room automatically qualifies as a recognised bedroom in a house offered for sale.

For new dwellings, the model building regulations propose 15 m² for the first bedroom and 10 m² for each additional bedroom. As this is a model intended for municipalities, the regulations actually adopted by the municipality concerned must be checked.

Floor area alone is not sufficient. Height, windows, ventilation, configuration and the authorised use of the room remain decisive.

Attics and mezzanines: check the area that can actually be counted

In an attic, the floor area can be considerably larger than the living area that is ultimately retained. Areas beneath roof slopes are not all counted in the same way, particularly where the ceiling height is below 2 metres.

An attic bedroom may therefore appear spacious on a floor plan while providing a smaller recognised living area. Natural light, access, ventilation and the criteria in the municipal regulations must also be examined.

For a more detailed explanation of the measurement method, read our article Living area in Luxembourg: how to calculate and verify it.

Annexes, conservatories and other converted areas

The same precautions apply to converted garages, annexes, conservatories and former technical rooms.

The fact that an area is insulated, heated and connected to the rest of the house does not guarantee that it has been authorised as living space. A conversion may require planning permission or constitute a change of use.

Before buying, it is advisable to compare the use presented during the viewing with the authorised plans and available documents. Before selling, this verification helps describe the property accurately and avoids creating incorrect expectations about its living area or number of bedrooms.

What impact can this have on the property’s value?

A converted ancillary area is not without value. A dry basement used as a gym, occasional office or leisure room can clearly differentiate a house on the market.

However, its value is not necessarily equivalent to that of additional recognised living space. Two houses with the same total floor area may therefore have different values if one contains recognised living areas while the other mainly comprises basements, low attic space or annexes.

Value also depends on the quality of the work, the usefulness of the area to buyers, the overall condition of the house, its location and the consistency between the actual situation and the available documents.

Before investing in building work

Before converting a basement, attic, garage or annex, consider the following questions:

Before buying a house with converted areas

When a listing presents a basement as a bedroom, studio, office or apartment, do not rely solely on the visible conversion.

Ask for:

An area that is not recognised as a bedroom can still be very useful. The important point is to understand its actual status before deciding how much you are prepared to pay.

Before selling a house with a converted basement or attic

Transparent presentation protects the credibility of the sale. Living space should be clearly distinguished from ancillary areas, and the current use of each area should be described without assigning a classification that cannot be verified.

This transparency does not necessarily reduce the property’s appeal. On the contrary, a buyer may appreciate a leisure room, workshop, converted basement or occasional office provided its nature is clearly explained.

Conclusion

Not all square metres are equal, but this does not mean that only recognised living space has value.

A converted basement, attic or annex can significantly improve the comfort of a house and appeal to buyers. However, conversion alone does not automatically turn the area into recognised living space or an official bedroom.

Before carrying out work, buying or selling, distinguish between actual use, the method used to calculate floor area and administrative compliance. This analysis helps avoid unpleasant surprises and supports a realistic valuation of the property.

FAQ: converted areas and living space in Luxembourg

Sources and further information