French Foundations: No Fixed Depth — Soil Study & Frost Zones

The requirement

France sets no fixed foundation depth. There is no single number in the Code de la construction et de l’habitation, and none in any free official text. Depth comes from a ground study and your site’s frost zone. The rules are NF DTU 13.1 and NF P 94-261. Anyone quoting one centimetre figure as “the French rule” is guessing.

Here is how it works. NF DTU 13.1 (September 2019) covers shallow strip footings. It is read with NF P 94-261 (June 2013, amended February 2017). That second standard is the French rule book for Eurocode 7. It splits France into hors-gel (frost-free) climate zones. The further from the coast and the higher up your site sits, the deeper your footing must go.

NF DTU 13.1 / NF P 94-261 · no fixed rule

1 footing
2 ground

Why no centimetre figure here. Both standards are private, paywalled AFNOR documents. We could not check the exact zone depths against the real text. And the figures floating around trade sites do not agree with each other. So we will not print a number we cannot stand behind. Get your zone and depth from a géotechnicien or a current copy of the standard. On many sites a ground study is required anyway. That is true anywhere with clay-shrinkage risk. The study sets your real depth, whatever the zone table says.

Width and concrete: design calls too. There is no fixed width table. The wall load and the soil’s bearing capacity set the width, worked out under NF DTU 13.1 and Eurocode 7. Width and concrete-grade figures do float around online. They trace back to the same paywalled standard, so check them against your own design.

Rebar cover: one for the engineer. On a reinforced foundation, the cover figure comes from Eurocode 2 (NF EN 1992-1-1). It depends on the durability and exposure class. That is the engineer’s call, not a number to lift off a page.

Work it out on site

Your ground study sets the depth. Your design sets the width. Once you know both, the concrete volume is just maths. Say you have a strip foundation to pour. These are example numbers only:

Total length of trench: 26 m
Foundation width: 0.45 m (example only, set by your design)
Foundation depth: 0.60 m (example only, set by your frost zone and ground study)

Volume = length × width × depth.

26 × 0.45 × 0.60 = 7.02 m³

So you would order about 7 cubic metres. Then add a bit for spillage and an uneven trench. Most builders tack on 5 to 10 per cent. Swap in your own numbers and the calculator does the sum.

Do it in 5 seconds

Part of the French building-codes hub — how the CCH and the NF DTU standards fit together.
Setting out the stairs above these footings? See French stair & guard-rail rules.

Sources

NF DTU 13.1 (September 2019) — Fondations superficielles et semi-profondes. Private AFNOR standard; execution rules for footing width, thickness and concrete. Catalogue at boutique.afnor.org.
NF P 94-261 (June 2013, Amendment 1 February 2017) — the French national application standard for Eurocode 7, governing the hors-gel frost-depth zoning system. Also a private AFNOR standard. Catalogue at boutique.afnor.org.

Read this first. Neither of the standards above is freely published, so the specific centimetre figures for frost-zone depth, footing width and concrete grade that circulate on trade sites are not independently confirmed against the primary text here — that’s exactly why this page gives none of them as a rule. Get a site/geotechnical investigation, and check your design against a current copy of NF DTU 13.1 and NF P 94-261 (or have an engineer do it) before you dig.

Frequently asked questions

Is there a minimum foundation depth in France?

No. France sets no single national figure. Depth comes from a required ground study and your site's hors-gel (frost-free) climate zone. The rules are NF DTU 13.1 and NF P 94-261, the French standard for Eurocode 7. No code book prints one depth for the whole country.

What's the hors-gel frost-zone system?

France is split into climate zones for frost depth under NF P 94-261. The further from the coast and the higher up, the deeper you must found. Both standards are paywalled AFNOR documents, so we can't confirm the exact zone depths. Get your zone and depth from your géotechnicien or the standard.

How wide does a strip footing need to be, and what concrete goes in it?

There is no fixed width. The wall load and the soil's bearing capacity set it, worked out under NF DTU 13.1 and Eurocode 7. Width and concrete-grade figures do circulate on trade sites. They trace back to the same paywalled standard, so check any figure against your own design.

What's the rebar cover on a reinforced foundation?

Not a figure we print here. Cover comes from Eurocode 2 (NF EN 1992-1-1), worked out from the durability and exposure class. A reinforced foundation is engineer-designed work, not a deemed-to-satisfy table. Check the standard, or leave it to the engineer who designed the reinforcement.

Why doesn't this page give a depth in centimetres?

Because there is no one true figure. Depth depends on your site's ground report and its hors-gel zone. Printing a single centimetre number would be guessing. Guessing on a foundation depth is how walls crack. Get a ground study done for your site.