House extensions on the Côte d'Azur: permits and tax
Adding a bedroom, glazing a terrace or turning the garage into a living room gives you space without a move. The mairie (town hall) measures all of it in square metres, and four numbers (5, 20, 40 and 150) decide how much paperwork you face.
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Get quotesOn this page8 sections
- Which extensions need nothing, a planning declaration or a full permit?
- When a garage or loft conversion needs a planning declaration
- Why glazing a terrace turns it into an extension
- Which TVA rate applies to an extension: 10% or 20%?
- What does the local building tax cost on a 20 m² extension?
- What pushes up the price of a house extension, and which insurance must you buy first?
- French terms you'll meet when extending a house
- Frequently asked questions about extending a house on the Côte d'Azur
Permits
Which extensions need nothing, a planning declaration or a full permit?
The size of the new floor area decides. Up to 5 m² you file nothing outside a protected area. From 5 to 20 m² you file a déclaration préalable (DP) everywhere. Between 20 and 40 m², a DP is enough only in an urban zone of the commune's PLU. The house must also stay at or under 150 m² in total. Otherwise you need a permis de construire, and so does anything larger.
The 150 m² figure is the surface de plancher of the whole house after the works, not just the new part. Past it, a private owner must use an architect. A company such as an SCI needs one for any permis, whatever the size.
Surface de plancher means closed, covered floor with more than 1.80 m of headroom. A DP gets an answer in one month, a permis in two for a house. Near a listed monument or in an old town, the ABF reviews the file and those become two and three months. Neighbours then have two months from the notice on site to challenge the decision.
Before you pay an architect for drawings, ask the mairie for a certificat d'urbanisme. It is free, and it freezes the rules and taxes that apply to your plot for 18 months.
Garage and loft
When a garage or loft conversion needs a planning declaration
Turning a closed garage into a room (aménagement de garage) creates surface de plancher even though the walls stand already. Over 5 m² that needs a DP. So does any change to the outside, such as a window or glazed door where the garage door was. The 150 m² architect rule still applies to the house total.
Some communes ask you to keep a parking space once the garage goes. That sits in the PLU, so ask the mairie before you commit to the plan.
A loft conversion follows the same logic. Once the space has more than 1.80 m of headroom it counts as floor area. Creating floor area needs a filing, within the same 5, 20 and 40 m² thresholds as an extension. A new roof window needs its own DP, even when the loft itself doesn't. Under an ABF perimeter, expect a say on the window's position and size.
Ask the contractor to price on the devis (written quote) the parts a conversion forces on you: insulation, a proper floor and heating for the new room. A garage slab is often not built to be a living floor, so ask how the builder will handle damp and levels.
Tell us what you want to add and we'll put you in touch with an English-speaking contractor or architect who quotes in writing.
Get quotesTerrace and veranda
Why glazing a terrace turns it into an extension
An open terrace or pergola follows lighter rules, set out on our terrace and pergola page. Once you close it in with glass or walls and cover it, it becomes a veranda. The mairie treats it as an extension, with the same 5, 20 and 40 m² thresholds and the same tax.
Two things follow. The veranda needs a filing that an open pergola would not, and it becomes taxable floor area. Adding glass sides to an existing pergola later triggers both, so tell the builder now if glazing is a possibility in a few years.
Ask the veranda supplier who files. Many include the paperwork, and some only supply the frame and leave the DP to you. Put the answer on the devis, with a copy of what was filed. If a required filing is skipped, the planning problem stays with you, and it can surface when you sell.
Also ask what the enclosed room will be used for. A glazed space with no heating is cold in January and hot in July. If you want a room you can sleep in year-round, the glazing, insulation and heating belong in the price from the start.
TVA
Which TVA rate applies to an extension: 10% or 20%?
On a home over two years old, most building work is taxed at 10% TVA (French VAT). Extensions are the main exception. A room built onto the house, or a raised roof, counts as new construction and takes 20% whatever its size. Work inside the existing walls that raises the floor area by more than 10% also takes 20%, unless it adds 9 m² or less.
For a garage conversion, whether the garage already counted as floor area changes the answer.
Ask the contractor to write the TVA (French VAT) rate on each line of the devis, and the reason for it. Our TVA guide covers the other cases. The gap between 10% and 20% is a tenth of the bill, so get the rate in writing before you sign.
Local tax
What does the local building tax cost on a 20 m² extension?
The taxe d'aménagement is a one-off tax on new closed and covered space over 1.80 m high. For 2026 the taxable surface is multiplied by 892 EUR per m². That figure is then multiplied by your commune's rate (1 to 5%, up to 20% in some sectors) plus the Alpes-Maritimes rate of 2.5%.
As an illustration, take a 20 m² extension in a commune charging 5%. The combined rate is 7.5%, so the tax is 20 x 892 x 7.5%, about 1,340 EUR. The bill arrives after completion and you declare the work online within 90 days.
Main homes get a 50% reduction on the first 100 m². A second home pays the full rate. Open terraces and pergolas pay nothing, while a veranda does.
A garage was usually taxable surface already, so converting it may create no new tax. Ask the mairie before you assume so.
Budget and insurance
What pushes up the price of a house extension, and which insurance must you buy first?
The ground comes first. On a hillside plot the builder may have to cut into the slope or build a retaining wall, and a narrow lane can mean small lorries, hand barrows or a crane. Ask what the foundation price assumes about the ground, and what happens if the digger hits rock or soft soil.
Matching the house costs more than building something plain. The same roof tiles, render and window style may have to be sourced, and the join between the old roof and the new one is where leaks often start. Ask how the builder will tie them together.
Some costs sit outside the builder's quote. Above 150 m² in total you pay an architect, and the taxe d'aménagement arrives after completion. Dommages-ouvrage is the owner's obligation, taken out before work starts. A private owner who skips it faces no fine, but at a sale within ten years the notary records that it's missing. Larger extensions must also meet new-build energy rules, so ask which apply to yours and how compliance will be shown.
Get at least two written quotes on the same drawings, with groundwork, foundations and the roof join as separate lines. Tell your home insurer about the project too. Running it from a distance is covered in managing a renovation from abroad, and an old village house in stone house renovation.
French terms
French terms you'll meet when extending a house
Key French terms for this service
Questions
Frequently asked questions about extending a house on the Côte d'Azur
If your question isn't here, send it with your request and we'll answer it directly.
Yes, it counts the total surface de plancher after the works. A 120 m² house with a 35 m² extension comes to 155 m², so you need a permis de construire and an architect, even though 35 m² alone would fit under a déclaration préalable in an urban zone.
After one month from a complete file (two in a protected sector) silence counts as approval. Keep proof of the filing date, display the panel on site, and remember that neighbours then have two months to challenge the decision.
No. The tax office sends you the bill after completion, and you declare the finished work online within 90 days. Put the amount in your budget before you sign. The glossary page shows how to contest a wrong surface or rate.
Yes, with a certificat d'urbanisme from the mairie. It's free, the information version is answered within one month and the detailed version within two, and it freezes the planning rules and taxes that apply to your plot for 18 months. Ask for the detailed version if you already know roughly what you want to build.
Yes. Tell your insurer before work starts, because the floor area and value of the house change. Each builder's décennale (ten-year building insurance) covers their own work. Dommages-ouvrage is separate and is the owner's obligation before the site opens.
Sources
Official sources for extension permits, TVA and the local tax
- Service-Public.fr: déclaration préalable and permis for an extension (F17578) The 5, 20 and 40 m² thresholds, the 150 m² total, the one and two-month answers and the roof window rule.
- Service-Public.fr: converting a garage into a room (F36776) A déclaration préalable over 5 m², and for any change to the outside of the garage.
- Service-Public.fr: surface de plancher (F2868) Closed and covered space with more than 1.80 m of headroom counts as floor area.
- Service-Public.fr: taxe d'aménagement (F23263) The 892 EUR per m² value for 2026, the 50% main-home reduction and the 90-day declaration.
- BOFiP: TVA on housing improvement work An addition or raised roof is taxed at 20%, as is other work raising the floor area by more than 10%, unless it adds 9 m² or less.
- Service-Public.fr: dommages-ouvrage insurance (F2032) The owner takes out the policy before work starts on an extension.
Rules checked against these sources in October 2026.