What it is and when it is obligatory
The seguro decenal is a material damage insurance guaranteeing, for ten years from acceptance, compensation for damage caused to the building by defects originating in or affecting the foundations, supports, beams, slabs, load-bearing walls or other structural elements, and directly compromising the building's mechanical strength and stability: exactly the perimeter of the LOE's ten-year clock. The cover follows the structural perimeter and does not extend beyond it.
Its obligatory nature comes from the law itself: the guarantee is required for buildings whose main use is housing, with the developer as the characteristic policyholder and the insured being the developer and the successive purchasers. The legal provision articulating it also foresees notarial and registry control: the notarisation of new housing works requires proof that the guarantee has been constituted. In other uses, offices, industrial, public facilities, the decenal can be contracted but is not required through this route, and its use responds to the developer's risk policy or to the demands of financiers and investors.
How it works: damage insurance, not liability insurance
The nature of the decenal explains its practical value. It is a damage insurance: once a covered structural damage manifests within the period, the insured claims the repair from the insurer without needing to prove any agent's fault, and it is the insurer who, having compensated the damage, is subrogated and claims back against the liable parties under the LOE's distribution. For the owner, the difference is substantial: getting paid first and letting the fault discussion happen between the insurer and the agents, instead of litigating for years against contractors or designers of uncertain solvency.
The counterpart is the policy's contours: deductibles, exclusions and the precise definition of the covered damage, which follows the legal structural perimeter, without extending to habitability or finishing defects except through expressly contracted complementary guarantees. The exclusions are worth reading before signing rather than when claiming.
The OCT: the risk auditor
The system's characteristic operational piece is the organismo de control técnico (technical control body). The insurer does not underwrite blind: it conditions the policy on a technical risk audit by an OCT, which reviews the design in its structural aspects, the geotechnical study and the structure's execution, issuing reports whose reservations condition the cover.
For the operation's calendar and budget, this has two translations. The OCT enters early: procuring it at the project's start, and not on the eve of acceptance, avoids both late reservations impossible to remedy and inspection extra costs on what is already covered up. And its reservations are managed as coverage risk: an unlifted reservation can translate into policy exclusions, exactly where the building can least afford them.
| Element | Content |
|---|---|
| Covered perimeter | Structural damage compromising mechanical strength and stability |
| Duration | Ten years from acceptance of the works |
| Nature | Material damage insurance, not liability insurance |
| Prior control | Technical control body auditing the risk during the works |
| Outside cover | Habitability and finishing defects, unless complementary guarantees are taken |
What it costs: orders of magnitude
The decenal's cost combines the premium and the OCT's cost, and both are calibrated on real risk: structural typology, geotechnics, height, the project's singularity and the quality of execution control. As a conservative order of magnitude for ordinary residential building, premium and technical control together usually sit around one percent of the construction cost, with the range moving upwards for singular projects or difficult ground and downwards for repetitive standard-risk developments; each operation must check its case against real offers.
The correct economic reading is not of the cost but of the counterpart: the decenal is the piece that makes the structural guarantee liquid, and its premium is the price of turning the LOE's longest clock into a right collectable without prior lawsuit. The premium is compared with the cost of a structural lawsuit.
Frequent errors
The first is discovering the decenal at the end: contracting OCT and policy with the structure already executed multiplies reservations, inspections and premium. The technical control body is engaged before the structure starts.
The second is reading the policy as total building insurance: the perimeter is structural, and habitability or finishing damage follows the ordinary liability regime except under complementary covers. Complementary covers are contracted expressly and carry their own price.
The third is neglecting the OCT's reservations during the works and inheriting them as coverage exclusions. Each reservation is resolved and documented before work proceeds.
The fourth is the self-developer who sells within the period without having constituted the guarantee they were exempt from for own use, meeting the requirement at the notary's door. The exemption lapses on transfer and the notary checks it.
Note: the regime cited is that of article 19 and the second additional provision of the consolidated LOE; premiums, deductibles and conditions are a matter for each policy and must be checked against real offers.