Before we talk wood or aluminium, let us talk town hall: most pergolas need a prior declaration (déclaration préalable), and almost nobody knows it. Here are the rules, the prices, and my opinion for our valleys.
A pergola looks harmless: four posts, some crossbeams, no walls. Yet in the eyes of French planning law, it is a building like any other. Putting yours up without the required formality means risking forced regularisation, or even demolition. The good news: the paperwork is simple once you know it. Here it is, followed by the choice of material and the budgets.
Everything turns on the pergola's . The thresholds, as of June 2026, are as follows.
| Ground footprint | Formality | Time to allow |
|---|---|---|
| Under 5 m² | None in the general case | - |
| 5 to 20 m² | Prior declaration of works (déclaration préalable) | 1 month processing |
| 20 to 40 m², lean-to, urban zone with a PLU | Prior declaration (extension regime) | 1 month processing |
| Over 20 m² (other cases) | Planning permission (permis de construire) | 2 to 3 months processing |
Two traps to know about. First, the 40 m² exception only applies to a pergola leaning against the house, in an urban zone covered by a : a freestanding pergola of 25 m² needs planning permission, even in town. Second, a lean-to pergola changes the façade: even under 5 m², the town hall can require a prior declaration on that ground. Ten minutes at the planning desk (service urbanisme) before signing a quote saves you months of trouble. On my projects, I am the one who puts the declaration file together with you.
This is the answer you will not find on the pergola sellers' websites: an open pergola, with no solid roof and no walls, creates no taxable floor area. No development tax (taxe d'aménagement, France's one-off tax on new structures), no property tax increase. Everything changes if you close it in: glazed or sliding walls reclassify it as a conservatory, which is taxable. And the carport is a case apart: it creates a parking space, taxed as such by the development tax, even open. That is not a reason to give it up, it is just a cost to know about before, not after.
Aluminium dominates the advertising with the bioclimatic pergola and its motorised adjustable louvres. It is a fine product, effective at adjusting the shade, but you have to compare like with like: count on €400 to €1,000 per m² fitted, so often €7,000 and more for 12 m². Wood plays in another category of price and spirit: a bespoke wooden pergola, sized for your façade and your use, sits between €3,000 and €10,000 fitted. Lean-to, it extends the house and shelters the terrace from rain coming off the slope; freestanding, it creates a place of its own in the garden, but calls for more serious anchoring.
My honest opinion: for our valleys, I stand up for wood. A motorised bioclimatic pergola is one more mechanism exposed to frost, snow shocks and breakdowns, with after-sales service that depends on a distant manufacturer. A Douglas fir or larch structure properly sized for the snow load never breaks down, gets repaired locally, and ages with the house instead of ageing against it. Aluminium makes most sense in the lowlands, for those who want shade adjustable at the push of a button.
In Gerde, Bagnères and the surrounding valleys, I have seen kit pergolas sagging after a single heavy winter. The wood was never the culprit: the sizing was. That is exactly the job of a mountain joiner, and it is what I detail on my pergola and carport page.
Ground footprint (emprise au sol), PLU, use class: these terms are explained in my wood glossary.
Does your project include a deck under the pergola? Read my advice piece which wood for a deck in the mountains too.
Rarely. Below 5 m² of ground footprint, no formality in the general case. From 5 to 20 m², a prior declaration at the town hall is enough. Planning permission is only required above 20 m², with one special case: a lean-to pergola in an urban zone covered by a PLU can stay under the prior declaration regime up to 40 m².
No, as long as it stays open: with no closed solid roof and no walls, it creates no taxable floor area. Watch out for the carport though: it creates a parking space, and as such it enters the calculation of the development tax (taxe d'aménagement). Closing a pergola reclassifies it as a conservatory, which is taxable.
Yes, if it is sized for it. In the mountains, that is the real subject: beam sections, anchorings and roofing must be calculated for the snow loads of your altitude. That is what separates a craftsman's pergola from a standard kit designed for the lowlands.
I design a pergola sized for your altitude, and I put the declaration file together with you. The quote is free. I speak English, so feel free to call or write in English.
+33 6 03 57 45 47A reply within 48 hours, or in writing: contact@agencementklein.fr
