Serious defect, affecting the quality of construction, which causes a degradation of the building which renders it unfit for the use for which it was intended, thereby potentially putting at risk, in totality or in part, its soundness and stability. This type of defect may engage the legal liability of the contractor, the architect and the engineer who, as the case may be, directed or supervised the work, and the sub-contractor for the work performed by him. It may also cause the application of contractual guarantees, including those of a guarantee plan.