Carlos III assigned Juan de Villanueva to create this building, which was executed between 1785 and 1797 designed to build suitable lodgings for the First Secretary of State, the Count of Floridablanca. With the creation of this building, the perimeter of the stone esplanade of the Monastery, the lonja, was closed.
The plot of land chosen was not an empty plot; the first Bourbons had permitted a good number of houses and kitchens for palace servants to be built there which, due to their "improper look", had to be demolished. In its construction, the design of Juan de Herrera was followed when solving the problem of the difference in height between the upper street, now known as Floridablanca and the lonja.
Just as in his design of the Casa de Infantes and in the Houses of Trades designed by Herrera, Juan de Villanueva proposed a freestanding building, separated at the sides by streets.
In the elevations, Villanueva – just as in all his works on the Royal Site – once again chose historical dimensions. Even the façade facing the lonja became an imitation of the Herrera-style Houses of Trades, echoing their rhythm and composition.
In 1797, a raised passage was constructed which joined it to the Second House of Trades. For a time it held the administration area and offices of the Patrimonio Nacional (National Heritage) in San Lorenzo de El Escorial and is currently completely occupied by private renters who use it as dwellings.
En 1797 se construye el paso elevado que lo une con la Segunda Casa de Oficios. Durante un tiempo acogió la administración y oficinas del Patrimonio Nacional en San Lorenzo de El Escorial y actualmente se encuentra totalmente ocupada por arrendatarios particulares que la utilizan como vivienda.