Le sous-traitant doit justifier d’un montant pour cette garantie au minimum égal, pour les ouvrages d’habitation, au coût des travaux de réparation des dommages matériels **de nature décennale** causés à l’ouvrage ;

This means that the subcontractor provides a guarantee to the amount of the repair costs expected to be incurred within 10 years.

Only Builtin Accredited Builders can offer their clients our comprehensive 10 Year Guarantee.
https://builtininsurance.co.nz/10-year-guarantee/

The Kriega 10 – Year Guarantee - FAQ’s
:
What does the guarantee cover?
The guarantee covers defects in material and/or construction to include seams, seam tape, zips, stitching and construction materials.
What is not covered by the guarantee?
The guarantee does not cover damage due to (fair) wear and tear, crash damage, accidental damage, rips, tears, abrasion, chemical or fuel damage, UV degradation, misuse or neglect.
https://kriega.com/10-year-guarantee-faq

11. Building Guarantees in France
:
11.2. Builders Ten Year Insurance - Assurance Décennale
The assurance décennale taken out by the builder contractor covers their liability in the event of defects arising during the ten year guarantee period.
The insurance is obligatory and there are severe penalties for a builder (or architect) who does not carry appropriate insurance.
https://www.french-property.com/guides/france/building/new-b...

The subcontractor must provide evidence of (or justiy) an amount for this guarantee which, in the case of residential buildings, is at least equivalent to the cost of repairing material damage incurred over ten years to the structure;
or
… provide a 10 year guarantee for the structure

I rather fear the Discussion box gets overlooked (it's not the first time I have felt this) so I'm posting an answer instead, though the credit goes to Bourth from some time back, in response to a question about "désordre de nature décennale" for which the translation "disorder covered by 10-yr guarantee", qualified further by "statutory 10-year guarantee for fabric and fixtures" if necessary.
https://www.proz.com/kudoz/french-to-english/law-contracts/1...

I suggest a variation on the previous proposal, replacing "covered by" with "FALLING UNDER". This came to mind at first because I was thinking that "dommages" could be sequential secondary damage, not the defect actually covered by the guarantee. But the Code Civil uses "dommage".

In seeking to find examples of "damage" resulting from "defects" (I found none) I came across this explanation of the garantie décennale):
https://larevue.squirepattonboggs.com/french-construction-la...

where I note they use the term "decennial liability" and use "falling under" :
"To give an example of “damage” intended by Article 1792; if a wall has been built, but later falls down, this would be considered as damage FALLING UNDER the decennial liability rule. Visible defects like cracks in, or discolouration of the plaster, would not."

French term (edited): [dommages matériels] de nature décennale [causés à l’ouvrage]

IOW the kind of damages than can reasonably (/statistically) be expected to occur during a 10 year period - only that "expected / probable amount of damage" has to be covered by this "guaranty" given by the subcontractor to the main contractor (which BTW is not the "decennial insurance" given to the buyer of the finished property)

If for example the building gets damaged by a once in 100 year storm there will be more damage to repair then after a once in 10 year storm - this "guaranty" must be enough to cover the "once-in-10 year level of damage" - if a "once-in-100 year storm" happens it's not this subcontractor's problem.

By analogy with "decennial" and "100-year flood", you could talk of the cost of repairing a "decennial" damage to the building.

This term is about the expected level of repairs that has to be covered by this guaranty given by one subcontractor, not about the insurance given to the final buyer.


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Note added at 5 hrs (2022-01-25 20:47:47 GMT)
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Le sous-traitant doit justifier d’un montant pour cette garantie au minimum égal, pour les ouvrages d’habitation, au coût des travaux de réparation des dommages matériels **de nature décennale** causés à l’ouvrage ;
=
.... has to prove/show that the amount covered by this guarantee ... is at least equal to the costs of repairing a decennial (/once in a decade) level of material damage to the building.


"la nature" des dommages matériels = a property / characteristic of the amount/ level of material damage.