On January 1st 1515, François I succeeded Louis XII. Six months prior, he had married the young Claude de France who had been raised in Blois and had very strong links with the château of her childhood. In the following month of June, the king named a treasurer « committed to keeping the accounts and making the payments for the buildings of the château of Blois". We have written statements of payments for the building up until September, 1518. It is likely that the work barely lasted beyond this date, as confirms a recent dedrochronological analysis (dating according to the study of the growth rings of the timbers) according to which the wood would have been cut between 1516 and 1518. Nevertheless, work was also done on the rafters in 1535. It is likely that the undertaking of Chambord in 1519, followed by the death of Claude de France in 1524, explains the king’s relative disaffection for Blois.

Who was the architect of this part of the château ? It is likely that François I, whose penchant for the art of architecture was well-known, gave precise instructions. But who conducted the project ? During these years, a former disciple of Giuliano da Sangallo, the Italian architect Domenico di Cortone, called Il Boccador (c.1465-1549), lived in Blois from 1512 to 1530. Appointed as the "King’s architect", he did a model for the project of Chambord in 1519 and later on was called to Paris in 1533 to build the new town hall. He was undoubtedly consulted about the construction of the François I wing, whose construction was entrusted to the master mason Jacques Sourdeau (died c. 1522). After working in Amboise in 1495, the Sourdeau was present in Blois from 1502. In 1516, the Queen Claude gave him some land to build his own home, and in 1518, he was mentioned as the "master mason of the work at the château of Blois", before being appointed at Chambord the following year.

The François I wing has a very different aspect according to whether you discover it from the street outside, which was laid out where the former gardens were found, or from the inner courtyard. Inside, the silhouette of the building follows the medieval tradition : a massive edifice, crowned by a high steep-sloped roof with dormer windows and an imposing polygonal staircase tower that serves the halls within. This traditional appearance can be explained by the fact that François I reused the foundations and even the walls of a medieval construction that he undoubtedly enlarged and elevated, and against which he applied a new facade.

The innovations are concentrated on the decoration of the staircase and the facade. The ornamentation was inspired by Italy and is characteristic of the early French Renaissance style. The facade is decorated by a complex pattern of horizontal mouldings and pilasters (flat columns applied to the wall) that embrace the window openings. The top of the elevation is surmounted by a massive cornice ( scallop motifs typical of classical art intermingle with medieval gargoyles) above which you can see a carved balustrade. This horizontality contrasts with the verticality conferred by the tall dormer windows, which are surmounteded by niches containing the statues of « putti » (naked infants inspired by antiquity) crowned by triangular pediments.

The projecting polygonal staircase offers a striking contrast between the heavy supporting buttresses and the lightness conferred by the wide open bays forming loggias that follow the spiral movement. These balconies served as new-fashioned theatre setting for court life where one could see and be seen : from the balconies, one could admire the festivities below, and from the courtyard, courtiers could observe the king inside his staircase.

The facade and the staircases are decorated with a multitude of royal emblems : the salamanders surmounted by crowns for François I, and the monograms F and C for the King and the Queen. There isn’t any regard for symmetry in this composition : the openings were done according to the requirements of the interior layout. This asymetry was furthermore accentuated by the destruction of a quarter of the wing on the western end (left side) due to the reconstruction undertaken by Gaston of Orléans in the 17th century. Originally, the staircase was found in the middle of the facade.

From the street outside, or rather from the location of the former vast terraced gardens done under Louis XII and enlarged by François Ier, you can admire the Facade des Loges. This facade ows its name to the numerous balconies which give way to the rooms inside. The elevation was inspired by an Italian model, the Loggia facade built by Bramante at the Vatican. However, whereas in Rome the galleries served as real passageways, the loggias in Blois are separate balconies that do not communicate one to another. The horizontality inspired by Italy was emphasized with the development of an attic storey which forms a gallery punctuated by columns running under the roof. On the other hand, the high central dormer window with the royal salamander is still very rooted in the French tradition. On the lower levels, the parapets of the loggias are decorated with the emblems of the King, his mother Louise de Savoie, and his wife Claude. On the overhanging turrets, one of which corresponds with an oratory, you can notice sculpted reliefs representing the labors of Hercules.

The interior layout of the François I wing was partially dictated by the choice to build the new building on either side of the medieval ramparts. On the courtyard side, the rooms occupy the formers spaces of a medieval construction, whereas the galleries and chambers opening onto the Façade des Loges were built on the outer side of the ramparts. The interior decoration of the royal apartments on the first and the second floors was completely recreated by Félix Duban in the 19th century. Nevertheless, in the King’s Hall, part of the sculpted decoration on the two ornate fireplaces and the door frame still remains from the 16th century. In addition, the so-called Queen’s study, which is actually the study or studiolo (place of study) designed for François I, is the only royal one in France from the Renaissance period that has kept its original woodwork, complete with its carved, gilded, and polychromed panels representing candelabrum motifs.