Your family is growing or you need a home office? A home extension is often more economical and less stressful than moving. In Luxembourg, several options are available: lateral extension, vertical extension, conservatory, loft conversion…
Possible Types of Extension
Lateral Extension (Ground Floor)
Building a new room attached to your house. This is the most common solution.
Ideal for: adding a bedroom, an office, a living space. Typical area: 15-50m² Average price: €1,800-2,500/m²
Vertical Extension (Adding a Floor)
Adding an extra level on top of your existing house.
Ideal for: doubling the surface without encroaching on the plot. Typical area: the entire footprint of the house Average price: €2,200-3,200/m²
Conservatory
A glazed extension, often between the living room and the garden.
Ideal for: gaining light, creating a winter garden. Typical area: 10-30m² Average price: €1,200-2,000/m²
Loft Conversion
Transforming unused attic space into living space.
Ideal for: bedrooms, an office, a playroom. Typical area: depends on the existing roof frame Average price: €1,000-1,800/m²
Building Permit: When is it Mandatory?
In Luxembourg, any modification to the ground footprint or the height requires a building authorization.
Permit required:
- Solid extension (masonry, timber frame)
- Vertical extension
- Conservatory over 10m² (depending on the municipality)
- Facade modification
Always check:
- Your municipality’s PAG (General Development Plan)
- The maximum COS (Plot Occupation Coefficient)
- The required distances to property boundaries
- The maximum height allowed
Time to obtain: generally 2 to 4 months.
Prices by Extension Type (2026)
| Type | Price/m² | 25m² Extension |
|---|---|---|
| Masonry extension | €1,800-2,500 | €45,000-62,500 |
| Timber frame extension | €2,000-2,800 | €50,000-70,000 |
| Vertical extension | €2,200-3,200 | €55,000-80,000 |
| Standard aluminium conservatory | €1,200-1,800 | €30,000-45,000 |
| High-end conservatory | €1,800-2,500 | €45,000-62,500 |
| Loft conversion | €1,000-1,800 | €25,000-45,000 |
These prices include: foundations, structure, insulation, standard finishes, connections.
Extension vs Vertical Extension: How to Choose?
| Criterion | Lateral extension | Vertical extension |
|---|---|---|
| Land required | Yes, available space | No |
| Structural study | Light | Mandatory and complex |
| Works duration | 3-5 months | 4-6 months |
| Price | Cheaper | More expensive |
| Permit | Simpler | More complex |
| Living there during works | Possible | Difficult (open roof) |
Choose a lateral extension if you have land and want to limit costs.
Choose a vertical extension if your plot is small or you want to preserve your garden.
The Steps of an Extension Project
1. Feasibility Study (2-4 weeks)
- Analysis of the plot and the existing structure
- Verification of planning constraints
- Budget estimate
2. Design and Quotes (3-6 weeks)
- Plans by an architect (mandatory if a permit is needed)
- Detailed quotes from companies
- Choice of materials and finishes
3. Building Permit (2-4 months)
- Preparing the application file
- Filing with the municipality
- Review and issuance
4. Works (3-6 months)
- Earthworks and foundations
- Structural work (structure)
- Connection to the existing building
- Second-fix work and finishes
5. Handover (1 week)
- Compliance check
- Lifting of reservations
- Handover of the keys
Average Timelines
| Phase | Duration |
|---|---|
| Studies and design | 1-2 months |
| Building permit | 2-4 months |
| Site preparation | 2-4 weeks |
| Works for a 25m² extension | 3-4 months |
| Works for a vertical extension | 4-6 months |
| Total | 8-14 months |
Can You Live in the House During the Works?
Lateral extension: YES
The works are outside; the house remains liveable. Expect noise and dust.
Conservatory: YES
Fast and minimally invasive construction.
Vertical extension: DIFFICULT
The roof is open for several weeks. Temporary accommodation is often necessary.
Loft conversion: YES
The works are confined to the top floor. Watch out for noise and dust coming down.
Increasing Your Property’s Value
A well-executed extension immediately increases the value of your property:
| Added surface | Estimated added value |
|---|---|
| 20m² | €60,000-100,000 |
| 40m² | €100,000-180,000 |
| 60m² | €150,000-250,000 |
The return on investment is generally positive, especially in Luxembourg where every m² is scarce.
FAQ
Can I build right up to the property boundary?
No. In Luxembourg, minimum distances apply (generally 3m or more depending on the zone). Check your municipality’s regulations.
Do I need my neighbours’ consent?
Not legally, but it’s recommended to avoid conflicts. Neighbours can submit observations during the permit review.
How much does an architect cost for an extension?
Expect 8-12% of the works amount for a full assignment (design + site supervision).
3% VAT for an extension?
Yes, if the extension is attached to a home more than 10 years old and it’s your primary residence.
