Ten-year structural warranty: what you really need to understand before signing

Many SME directors view decennial insurance (the insurance that guarantees the repair of damage compromising the building's stability for ten years) as a simple administrative formality. It is often treated as just another line on a site checklist, a document slipped into a file to release a payment or satisfy a project owner. This approach is based on a dangerous illusion: the belief that possessing a valid certificate guarantees automatic compensation in the event of a major problem. The operational reality is far more complex because a certificate is merely a promise of intervention, subject to conditions so strict that they can render the coverage completely ineffective at the very moment you need it most.

The legal framework: a rigid structure with no exceptions

To understand the stakes, we must return to the fundamentals without getting lost in them. Everything is based on the Spinetta Law of 1978, which establishes a presumption of liability for all builders operating in France. This responsibility lasts for ten years starting from the handover of the works (the formal act by which the client accepts the project, with or without reservations). The law is clear: you must have taken out your contract before the opening of the first site, under pain of civil sanctions and penalties. You cannot regularize a situation after the fact; the risk must be carried by an insurer from the very first shovelful of earth.

The certificate is not your contract: the activity trap

The most common mistake is reading only the first page of your insurance certificate. This document summarizes your guarantees but never details the real scope of your coverage. The breaking point is almost always found in the nomenclature of activities. If your contract states that you are insured for "general masonry" but the incident occurs during a "metal framing" service that you performed as an ancillary task, the insurer will systematically refuse coverage.

This is not a matter of bad faith on their part, but a strict application of the declared risk. At Lesto, we often see companies that have evolved their technical offerings without ever updating their insurance policy. A company that moves from interior renovation to the construction of complex structures radically changes its risk profile without realizing it.

An insurance policy that does not precisely cover what your teams do on the ground every morning is a useless expense, not a protection.

The risk of under-declaration: the proportional premium rule

The amount of your insurance premium is calculated based on your projected turnover (your annual revenue). For a fast-growing SME, this figure can quickly become obsolete. If you declared a turnover of 5 million euros but ultimately achieve 8 million, you might think that a simple adjustment at the end of the year is enough. This is incorrect.

In the event of a serious incident (a claim) occurring before this adjustment, the insurer will apply what is known as the proportional premium rule. This means that if 30% of the premium is missing compared to your actual activity, the insurer will only pay 70% of the compensation. For structural damage amounting to several hundred thousand euros, the remaining cost to be paid by you can be enough to permanently weaken the cash flow of even a solid SME.

Subcontracting: a responsibility you never delegate

Another blind spot concerns the use of subcontractors. Many directors believe that if a subcontractor makes a mistake, the subcontractor's insurance will pay. Legally, regarding your client, you remain the sole party responsible for the proper execution of the works. If your subcontractor is uninsured or poorly insured, it is your own decennial contract that must cover the damage.

It is imperative to check not only the existence of a certificate for your service providers but also its validity for the specific lot they are handling. The failure to monitor your subcontractors' insurance status is a major operational risk that few companies manage with the necessary rigor.

Three questions to evaluate your current coverage

Before renewing your contract or signing a new one, you should be able to answer these three questions with certainty.

First, do my declared activities exactly match my current and future service catalog? You must track discrepancies between insurer jargon and the technical reality of your sites. A poorly chosen word in the special conditions (the document that personalizes your contract) can be enough to void a guarantee.

Second, is my declared turnover consistent with my growth trajectory over the next twelve months? Insurance should be viewed like a garment that you buy slightly too large so as not to be restricted by the first quarter. It is better to adjust your insurance budget upwards than to suffer a reduction in compensation during a crisis.

Third, what is my coverage limit (the maximum amount the insurer will reimburse) per claim and per year? If you work on high-value structures or sensitive industrial sites, a standard limit may turn out to be derisory. You must align your insurer's reimbursement capacity with the value of the projects you handle.

A reversed vision of risk

Most brokers offer ready-made insurance contracts, hoping that your company fits into predefined boxes. At Lesto, we reason in reverse of the market. We start by analyzing your real risks, your internal processes, and your client typology, then we look for or build an adapted coverage. The goal is not just to be "in compliance" with the law, but to be truly protected against the hazards that could stop your growth.

Decennial insurance is too technical a subject to be left to the chance of a quick sign-off on the corner of a desk. It is a lever for sustainability that requires constant attention, especially when your structure changes scale. Taking the time to dissect your special conditions today means sparing yourself a legal battle lost in advance tomorrow.

Lesto — the first AI-native French broker

Your certificate is a legal document, but your contract is a financial promise whose solidity you must imperatively verify before the first wall rises.