He was a prominent theoretician of urban planning in Madrid in the late 19th century, particularly in addressing the problem of housing workers as the city modernized and its population grew.

Later he abandoned his youthful idealism and became a successful and respected architect who created eclectic designs of major new buildings and renovations for public and private clients.

His training during the period of the "Sexenio Democrático" (1868–1874) was influenced by ambitious urban development projects for Madrid proposed by individuals such as Ángel Fernández de los Ríos (1821–1880).

In 1876 he became editor of the society's official organ, the Revista de la Arquitectura Nacional y Extranjera (Review of National and Foreign Architecture).

[1] Belmás presented his ideas about hygiene, urban planning and economical housing at the first National Congress of Architects in 1881, including the concept of working-class neighborhoods with single-family homes connected to the city using new forms of transport.

[4] In 1881–1885 Belmás undertook redesign of the Ministry of Development for the School of Arts and Crafts on the Paseo de la Infanta Isabel, Madrid.

[4] In February 1885 the Ministry of the Interior called for designs by Spanish architects for new houses for the poor, which had to cost no more than 1,500 pesetas and be as strong as possible against future earthquakes.

He wrote that "even if the house fell and rolled, its frame would remain locked like a boat that suffered the hard attacks of the raging waves of the sea".

[6] Well-known architects such as Francisco Jareño y Alarcón and Juan Monserrat Vergés cast doubts on whether the houses would be adequate for the harsh climate of the region.

[6] The five designs by Belmás Estrada followed similar construction techniques and were between 40 and 150 square metres (430 and 1,610 sq ft) in area.

[5] The houses had solid foundations, strong frameworks, reinforced corners and other features designed to reduce risk of collapse.

[10] In 1887 Belmás tried to manage development of an extension of the Pacífico neighborhood on Madrid, where he built a house for himself, but the project ran into financial problems.

[11][c] Between 1890 and 1896 Belmás was involved in a speculative development of a neighborhood of townhouses called "Madrid Moderno", which ran into many bureaucratic obstacles.

[13] In 1894 he played a key role in the foundation and initial development of the Ciudad Lineal (Linear City) urban proposal, promoted by this company.

[1] Belmás advised Fernando Navarro in his construction of the Palacete Rodriguez Quegles in Las Palmas, Gran Canaria, a small Art Nouveau place.

He was decorated with the Grand Cross of the Order of Isabella the Catholic, and contributed to the 1911 regulations for construction of single-family public houses in Madrid in the early 20th century.