In 1912 the Casa Thomas was extended to its actual size by Domènech's son-in-law, Francesc Guàrdia i Vial, who moved the two bodies of the crown to the new roof, built two grandstands on the old floor and designed a façade that links in a textual way with the primitive work. The two lower floors of the building are still preserved as designed by Lluís Domènech i Montaner.

Domènech carried out a number of renovation projects for his political colleagues. Francesc Macià, a military engineer and politician who became president of the Generalitat, commissioned him to renovate the interior of his house in Lleida, the Macià chalet. It is the last work Domènech carried out in Canet de Mar. As was the case with most of his works of this period, he had the collaboration of his son Pedro and his son-in-law Francesc Guàrdia. The Domènech family had their second residence in Canet de Mar, in the old Rocosa country house. This building did not have enough space to house the architect's large family and his studio. In 1877, they bought two houses on the corner of Riera Gavarra and Riera de Buscarons, which were connected to the house by the rear courtyards. Masia Rocosa became the architect's office and workshop and the new building the family residence. A first unrealised project is preserved at the Fons Cabruja in Canet de Mar. In 1918, a building permit was requested for the renovation and restoration of the Domènech house of the project that was finally carried out. The original building, on a corner at the confluence of the two streams, was two small 17th-century buildings. The previous constructions were not demolished, but a large part of the walls were reused. Domènech went up again and redistributed and ennobled all the openings, adding a hall with exposed brick arches at the top and monumentalising the chamfered corner with a tribune decorated with floral and zoomorphic elements. Inside the house, all the rooms were renovated, ensuring that all the rooms had windows on the outside. A staircase with ceramic risers connects the ground floor with the first floor, leading to a double-height entrance hall. On the floor of this space is a walk-through skylight that brings light from the upper skylight to the ground floor. A spiral staircase connects this space with the perimeter balcony on the first floor. Several rooms in the building contain the plaster casts of some of the sculptural works in its buildings. In 1980, it was renovated to house a bank and an extension was built in the garden. After the transfer of all the buildings to the Town Council and a second refurbishment in 2011, it is now a facility that houses the Domènech i Montaner House-Museum in Canet de Mar.

Es tracta d'una gran mansió de tres cossos bàsics, dos simètrics a banda i banda i un central més elevat. El cos central és de planta rectangular i dues torres, una adossada i l'altre sobresortint de la coberta. La primera és de dimensions més grans, de planta quadrada té finestres de mig punt a la façana. La segona és a mode de campanar amb una teulada a quatre vessants acabada en punta i penell al cim. La disposició de la coberta del cos central és a quatre vents tot i que varia a la part central i anterior. El material emprat és la teula àrab envernissada de dos colors. La façana principal presenta un portal rodó dovellat seguint la tradició de les cases pairal de la zona, i una balconada amb pedra treballada a mode d'escultura amb dues figures humanes. A la porta del balcó d'una sola obertura, testera recta i llinda d'una sola peça. Hi trobem una barreja d'estils amb columnes jòniques, una llinda amb traces gòtiques amb un medalló d'estil barroc, columnetes als brancals i un entaulament decorat amb un relleu de factura neoclàssica. Les obertures es disposen de forma simètrica respecte l'eix central. En les cantonades hi ha medallons de pedra sota una cornisa de maó vist. En relació a les façanes laterals, hi trobem dues galeries amb vuit arcades circulars amb columnes de pedra eixamplades a la part central. Les teulades acaben amb ràfecs sostinguts per cartel·les de maó que formen diferents sanefes decoratives. Totes les obertures combinen l'arc rebaixat o la forma rectangular. Destaca també la decoració d'obra vista així com el joc volumètric de les cobertes. La sincronia entre les diferents parts de l'edifici està molt aconseguida. Aquesta diversitat de formes, elements, materials i tècniques és típicament modernista, però tots ells estan disposats d'acord a una gran sobrietat neoclàssica. L'any 1918, Francesc Simon, copropietari de l'editorial Montaner i Simon i responsable, juntament amb Ramon Montaner i Vila i Josep Roqueta i Bes, de la construcció del balneari Roqueta, va decidir la construcció de la seva residència d'estiueig. Aquesta torre és, junt amb d'altres, un clar exponent d'un procés que, amb l'obertura de la carretera a mitjans de segle passat i la descoberta d'aigües sulfuroses el 1874, feu capgirar l'estructura urbanística de Tona. Gran part de la burgesia barcelonina va triar aquest municipi com a lloc per a estiuejar. Al passar llargues temporades a Tona, es construïren les seves pròpies torres o xalets. Aquest procés va consolidar-se amb la inauguració de l'Estació de tren de Balenyà i l'acabament de la xarxa de carreteres que comunicaven Tona amb Barcelona i Manresa. El turisme d'estada i de residència tingué una gran importància per l'economia i per la imatge de la població al segle XIX i principis del XX.

The building is made up of three distinct but interrelated bodies. It is a villa surrounded by a garden. The bodies have two or three storeys (the central one), covered with hipped roofs and with an eave supported by a wooden beam. The openings have straight or semi-circular arches. The gates or accesses to the garden stand out. The main doorway has a semicircular arch, voussoir-shaped and with stone imposts. On the main façade there is another doorway over which there is an overhang or balcony supported by columns with cylindrical shafts and a base and capitals with quarter-round mouldings. All the elements, harmoniously combined, contribute to giving the house a stately air: the quality of the materials, staircases, balconies and terraces, etc. A tower, with a hip roof, stands out on one of the lateral bodies. Tona began its expansion with the construction of the road to Barcelona and the discovery of sulphurous waters in 1874, which favoured the creation of several spas and the attraction of bourgeois foreigners, who enjoyed both curing illnesses and forming an enclave for cultural and leisure activities. On the extension of the Carrer Major - the old royal road from Barcelona to Vic - and the road, some islands with the characteristics of a garden city constitute a small enclave of summer towers, built between 1918 and 1923, when the Catalan Art Nouveau in decline and the plethoric noucentisme were blending together in a harmonious symbiosis of forms, composition and ornamentation. This house is one of the houses that the industrialist Joan Llussà i Duran had built at the beginning of the 20th century for himself and his family. It coincided with the improvement of communication routes, both by road and by train. This new infrastructure helped the great industrialists of Barcelona, such as Joan Llussà himself, Santiago Simon and Joan Maragall, the poet, to invest in construction or to spend long periods in Tona, increasing the prestige of the city.