By means of the declaration of new construction, the owner of the land, or of a surface right, or of another pre-existing construction, whether or not registered as a registered property, in the Property Registry, records in a public deed the fact of having planned, begun, or completed buildings, new plants, or improvements thereto, with the purpose of documenting the acquisition title and, if possible to meet the legal requirements, registering said modification in the Property Registry, thus achieving a greater degree of legal security for the construction of new construction.

The declared new work can be qualitative or quantitative. The deed of declaration of new construction may include only qualitative or only quantitative modifications in the registered property, or it may include modifications of both kinds, that is, qualitative and quantitative, and this occurs when, in addition to the declaration of new construction, the deed also includes the division (material or horizontal) of the plot or surface property susceptible to construction.

The new work must necessarily be declared in a public deed executed before a notary. This is required by art. 3 of the Mortgage Law (L.H.) as an essential requirement for its registration, although exceptionally, the Public Administration can make its declarations of new construction and horizontal division through administrative certification if they are supported on plots of its property, and as long as they do not affect third parties (art. 206.2 of the LH).

The declaration of new construction can be done in one of three ways:

The legislation that especially regulates the declaration of new construction is found in art. 208 of the Mortgage Law, and art. 308 of the Mortgage Regulation, although the true legal basis of the acquisition title by declaration of new construction is the right of accession, which is basically regulated in arts. 358 to 361 of the Civil Code. Likewise, arts. 45 to 55 of the Urban Mortgage Regulations of 1997, and art. 20.1 of the Building Planning Law of 1999. For their part, the different land laws, state and regional, establish their own complementary requirements to the deed of declaration of new construction, very similar in all of them.