3% VAT
How much does a house extension cost in Luxembourg, and how do you get one built in 2026?
In Luxembourg, a house extension costs €1,300 to €3,000/m² depending on the system: prefabricated €1,300 to €2,600, masonry €1,800 to €3,000 — that is €36,000 to €60,000 for 20 m² in masonry. It needs a building permit from the mayor and qualifies for 3% VAT when it enlarges your main residence.
Your result in 2 minutesFree simulator Estimated budget€VAT saving€Property value gain€ Instant result, no obligationStart the simulation →- Price per m² (market survey 2026): prefabricated (timber frame, modular) €1,300–2,600 · masonry €1,800–3,000 · four-season veranda €1,800–3,500 · adding a storey €2,800–3,500
- Foundations and slab: €5,000 to €15,000 depending on the soil, almost never included in a kit or module price
- Build time: 3 to 5 months prefabricated, 8 to 14 months in masonry, plus the permit
- Building permit (autorisation de bâtir): issued by the mayor; no answer after 3 months counts as a refusal; valid 2 years, extendable once by 1 year
- 3% VAT instead of 17%: an extension counts as « creating » housing, with no minimum building age; benefit capped at €50,000 per dwelling
- Klimabonus: the new part gets no grant; an air-to-water heat pump replacing a fossil boiler gets €12,000 if ordered before 30 June 2027
- Energy performance certificate (CPE): mandatory after an extension
Which type of extension: ground-floor, extra storey, veranda or prefab?
The right type of extension depends first on your plot and your municipality: a ground-floor extension is the simplest and cheapest per m², adding a storey is the answer when the zoning plan leaves no ground coverage, and a veranda suits a light-filled living space rather than a bedroom.
| Type of extension | Best for | Indicative price | Build time | Watch out for |
|---|---|---|---|---|
| Ground-floor, masonry (concrete block, brick) | Durable living space, continuity with a masonry house | €1,800 – 3,000/m² | 8 – 14 months | Roof junction and settlement between new and old foundations |
| Ground-floor, prefabricated (timber frame, 3D modules, kit) | Short works while you live in the house | €1,300 – 2,600/m², excl. foundations | 3 – 5 months | Foundations, connections and junction often not in the price |
| Extra storey (vertical extension) | Plot with no ground coverage left | €2,800 – 3,500/m² | After a structural survey | Existing foundations and walls must carry the new floor |
| Veranda | Bright room opening onto the garden | €1,800 – 3,500/m² installed (four-season) | Manufacture 8 – 16 weeks, fitting 1 – 3 weeks | Glazing and thermal break for year-round use |
Adding a storey costs on average 30 to 50% more per m² than a ground-floor extension: the foundations and load-bearing walls must be checked, the roof removed and a staircase created. A structural engineer runs that calculation before any quote, and the roof structure has to be rebuilt. Timber frame, lighter than masonry, is often chosen for this.
A prefab extension (timber frame, 3D modules or kit) costs €1,300 to €2,600/m² excluding foundations and is built in 3 to 5 months, against 8 to 14 in masonry. The cost of each system, what a kit price leaves out and the choice between timber and concrete are set out in our dedicated guide.
Before building out, look up: an attic conversion costs €20,000 to €35,000 when the headroom and roof structure allow it. The same logic applies to an attached garage: turning a garage into living space adds square metres without extending.
House extension cost in Luxembourg in 2026: per m² and for 20 m²
For 20 m², budget €36,000 to €60,000 for a turnkey masonry extension and €30,000 to €52,000 for a prefabricated timber frame, plus €5,000 to €15,000 for foundations and the utility connections when they are not included in the offer.
| System | Price per m² | Budget 20 m² | Budget 30 m² | What the price usually covers |
|---|---|---|---|---|
| Masonry | €1,800 – 3,000 | €36,000 – 60,000 | €54,000 – 90,000 | Shell, roof, fit-out |
| Prefabricated (timber frame, modular) | €1,300 – 2,600 | €26,000 – 52,000 | €39,000 – 78,000 | Structure and insulation; foundations, connections and junction often extra |
| Extra storey | €2,800 – 3,500 | €56,000 – 70,000 | €84,000 – 105,000 | After a structural survey; staircase and roof to be priced |
| Veranda | €1,800 – 3,500 | €36,000 – 70,000 | — | Installed; slab and heating often extra |
What comes on top of the price per m²
- Foundations and slab: €5,000 to €15,000 depending on the soil, for every prefabricated option.
- Opening the existing wall, connections (water, electricity, heating, drainage), staircase: quoted separately — the item catalogue prices leave out.
- Architect: 8 to 15% of the works depending on the assignment, invoiced at 17% VAT — see architect fees in Luxembourg.
- Energy performance certificate after the works: unregulated price, around €500 to €600 for a house.
These are market ranges surveyed in Luxembourg in 2026, excluding VAT, for a detached-house extension. Site access, soil and the junction with the existing house move them; only a quote issued after a site visit binds the company. For prefab options in detail, see prefab extension costs; for a glazed room, veranda costs.
Worked example. 1975 house lived in by its owners, 25 m² masonry extension at €2,400/m²: €60,000 excluding VAT. At 3% VAT the tax is €1,800 instead of €10,200, a saving of €8,400. Architect fees (10%, i.e. €6,000) stay at 17% VAT: €7,020. Total: about €68,800 including VAT, with foundations inside the shell price if the quote says so. If the oil boiler is replaced at the same time by an air-to-water heat pump ordered before 30 June 2027, Klimabonus pays €12,000, plus €1,500 for removing the tank.
Market benchmark: in the second quarter of 2026 an existing flat sold for €7,795/m² on average and a new-build flat for €9,809/m² (Observatoire de l’Habitat). Creating square metres at home is therefore 2.5 to 5 times cheaper than buying them.
Kitchen, master suite, home office: what the room changes to the budget
What the room is for weighs as much as the building system: a « dry » room (office, living room, playroom) only needs electricity and heating, whereas a kitchen or shower room needs water supply and drainage run back to the house’s networks.
| Room created | What it involves | Item to watch |
|---|---|---|
| Larger kitchen | Water supply, drainage with a fall, cooker-hood outlet, dedicated circuits | Fitted kitchens are excluded from 3% VAT: 17% on the units (see kitchen costs) |
| Master suite with shower room | Drainage, bathroom ventilation, sound insulation towards the house | Distance to the existing soil stacks |
| Home office | Electricity, network, daylight | The cheapest room to equip |
| Living room opening onto the garden | Large glazed opening, opening in the existing wall | Lintel or beam sized by a structural engineer |
| Playroom, multi-purpose room | Dry room, hard-wearing floor, plenty of sockets | Plan for a future partition (bedroom) |
Building permit for an extension: what your municipality checks
A habitable extension needs a building permit (autorisation de bâtir) issued by the mayor of your municipality, who checks it against the general development plan (PAG), the detailed development plan (PAP) and the building regulations: setbacks from boundaries, ground coverage, height, external appearance.
- Timeline: no statutory processing time. Without a decision after 3 months, the application can be treated as refused (implied refusal). « Silence means consent » does not exist yet: draft bill 8480, which would introduce it, has not been passed.
- Validity: 2 years from the permit, with a single 1-year extension (rule in force since 11 November 2024).
- Display and appeals: the mayor’s certificate must be visible from the street during the works; third parties have 3 months from the display to appeal.
- Small outbuildings: the model regulation recommended to municipalities exempts sheds, carports and greenhouses under 12 m² and requires a simple declaration from 12 to 20 m² — but only if your municipality has adopted it; the City of Luxembourg requires a permit for any new construction.
- Special cases: listed building, written authorisation from the Minister of Culture (answer within 4 months); green zone, authorisation from the Minister of the Environment; co-ownership, vote of the general meeting (3/4 of the votes for additions).
The 20 or 40 m² thresholds quoted on French websites do not apply in Luxembourg: only your municipality’s regulation says what is exempt, declared or subject to a permit. File the application before ordering a kit or modules, never after. The full procedure is in our guide to building permits and works declarations.
Financing an extension: home-improvement loan, 3% VAT and grants
An extension is financed with a standard bank loan — mortgage or home-improvement loan — made lighter by 3% VAT; the state’s Klimaprêt does not cover the extension itself, only the energy renovation of the existing part once Klimabonus has been granted.
3% VAT: the conditions for an extension
- An extension counts as creating housing under the housing VAT rules: no minimum building age, but the owner must use it as their own main residence. Extending a let property does not qualify.
- The benefit is capped at €50,000 per dwelling across all works over the dwelling’s lifetime: check your remaining balance on MyGuichet.lu.
- Still at 17%: architect and engineer fees, fitted kitchen, furniture, outdoor landscaping (except direct access).
- To be invoiced directly at 3%, the company files the approval request with the AED before the works and you countersign it (quotes of at least €3,000 excluding VAT). The home must remain your main residence for 2 years. See our guide to 3% VAT.
Home-improvement loan or mortgage
For €30,000 to €100,000 of works, banks offer either a personal home-improvement loan or a mortgage secured on the house; the latter runs over a longer term. Have the building permit and detailed quotes ready: they are the documents the bank asks for to set the amount.
Klimaprêt and Klimabonus: for the existing part
Klimabonus funds energy renovations of buildings more than 10 years old: the new part does not qualify, but the extension works are the right moment to insulate the existing walls or roof (flat-rate grant per m², approval in principle required before works), replace windows (€80/m² until 30 June 2027) or swap the boiler for a heat pump (€12,000 air-to-water, €14,000 ground-source if ordered before 30 June 2027 — see heat pump grants). As soon as the renovation covers more than one element, an approved energy advisor is mandatory. The Klimaprêt then covers 1.5% of interest per year on up to €100,000 over 15 years, with no income condition.
The VAT approval and the Klimabonus approval in principle (insulation, windows, ventilation) must be requested before work starts. A heat pump, on the other hand, is declared after installation, with no prior approval.
Energy certificate and insulation: making the most of the extension works
After an extension, a new energy performance certificate (CPE, « energy passport ») is mandatory; it rates the home from A+ to I on three indicators (primary energy, thermal insulation, CO₂) and is valid for 10 years.
The CPE is issued by an architect or consulting engineer registered with the OAI, or by an approved expert. For an extended building, a supplement based on actual consumption is provided within 4 years, without affecting validity. If the extension goes with insulating the existing house, the Klimabonus insulation grant rises by 20%, 30% or 50% when the insulation class reaches C, B or A with a gain of at least two classes, proven by a CPE before and after the works. More in our energy performance certificate guide.
Steps and timeline of an extension project
Allow 3 to 5 months of works for a prefabricated extension and 8 to 14 months in masonry, plus the design stage and the municipality’s review of the permit, which has no statutory deadline.
Check what the municipality allows
PAG and PAP for your plot (available on geoportail.lu) and building regulations: remaining coverage, setbacks, height, imposed materials.
Have the project designed
Drawings by an architect, structural survey as soon as a load-bearing wall is opened or a storey added.
File the permit application
Before ordering any kit, module or window.
Compare three quotes on the same scope
Foundations, connections and junction included; have the VAT approval filed and, for insulating the existing house, the Klimabonus approval in principle.
Carry out the works
Foundations, structure, opening and connection to the house, fit-out; permit certificate displayed throughout.
Hand-over, energy certificate, grant claims
The Klimabonus payment claim can be filed up to 4 years after 31 December of the invoice year.
Request quotes for your extension
Floor area, use of the room, site access: describe your project and receive 3 quotes from companies established in Luxembourg, priced on the same scope. Free and without obligation. For a first order of magnitude, the renovation simulator gives an estimate in a few minutes. If you use separate trades, such as a mason, carpenter or roofer, find a verified tradesperson for each trade.
Your extension, priced by verified companies
Reply within 48 working hours, foundations and connections included in the request.
Frequently asked questions about house extensions in Luxembourg
What total budget should I plan for a 20 m² extension in Luxembourg?
For 20 m², budget €36,000 to €60,000 excluding VAT for a turnkey masonry extension, or €30,000 to €52,000 for a prefabricated timber frame plus €5,000 to €15,000 of foundations. Add the connections and the opening in the existing wall (quoted separately), 8 to 15% in architect fees and around €500 to €600 for the final energy performance certificate.
Is a house extension invoiced at 3% VAT?
Yes, if the extension enlarges your main residence: the tax authority treats it as creating housing, with no minimum building age. The benefit is capped at €50,000 per dwelling, and architect fees, fitted kitchens and outdoor landscaping remain at 17%. The company must obtain AED approval before the works; otherwise you pay 17% and claim a refund.
Can I finance an extension with a home-improvement loan or the Klimaprêt?
An extension is financed with a standard bank loan: a personal home-improvement loan for a small amount, a mortgage for larger works. The Klimaprêt only finances the energy renovation of a home more than 10 years old that has already received Klimabonus: the state then pays 1.5% of interest per year, on up to €100,000 over 15 years.
How much floor area can I add to my house in Luxembourg?
There is no national figure: your municipality’s PAG and PAP set the remaining ground coverage, the setbacks from boundaries and the permitted height. Check your plot on geoportail.lu, then have it confirmed by the planning department or your architect before drawing up the project.
How much does adding a storey cost compared with a ground-floor extension?
Adding a storey costs around €2,800 to €3,500/m², 30 to 50% more than a ground-floor extension, because the existing structure must be checked, the roof rebuilt and a staircase created. It uses no land, however. A reliable price starts with a structural survey.
Extension or attic conversion: which is cheaper?
When the roof structure and headroom allow it, an attic conversion costs €20,000 to €35,000, far less than an extension of the same size, which exceeds €30,000 from 20 m². If the ridge height is too low or the roof uses trussed rafters, a ground-floor extension or an extra storey becomes the only option.