He is credited with having introduced the French style to American building construction, notably the mansard roof and all its decorative flourishes.

Trained at the École des Beaux-Arts, Paris, he designed virtually every type of Victorian structure—cottages, mansions, townhouses, apartment houses, hotels, tenements, banks, stores, churches, schools, libraries, offices, factories, railroad stations, and a museum.

After Catherine's death in 1861, Lienau married Harriet Jane Wreaks in 1866 and they had two children:[1] Eleanor F. and Jacob Henry.

In 1935, J. Henry donated about 800 of his father's professional drawings, photographs and other original documents to the Avery Library of Architecture and Fine Arts at Columbia University.

Lienau was one of a relatively small group of trained architects, of whom the majority were fairly recent arrivals from Great Britain and the continent.

All brought with them to the New World the traditions of the Old, but Lienau differed from his colleagues in one important respect: Molded by his early Danish and North German environment, and by years of study in various German art centers and in Paris, Lienau had a point of view more international than theirs—a rarity in an age of ardent nationalism.

Thus, a fusion of traditions enabled him to adapt quickly to life in America and to deal successfully with the demands of an increasingly eclectic age.

Another point that should be stressed, since it has long been ignored: It was Lienau, not Richard Morris Hunt, who was the first to bring to the United States a mind and a hand that was shaped, through contact with Henri Labrouste, by the French Beaux-Arts tradition.

Lienau's career provides a dramatic illustration of the contributions made by the professionally trained European architect to American architecture.

His chief importance to American architecture of the period from 1850 to the mid-1980s lies not in his use of the Second Empire mode per se, nor in his general eclecticism, but in the classical orientation of his entire practice.

His work represents a continuing current of conservatism in American architecture, which for a time was submerged beneath the more dominant picturesque modes of the period, the High Victorian Gothic and the Second Empire—the latter quite as anti-classical in its later style phase as the former.

He served as a bridge between the classical traditions of design of the second quarter of the 19th century and their re-emergence in the 1880s of the movement led in New York by the firm of McKim, Mead & White.

From simple cottages to great mansions, Lienau used many modes to express his own ideas and the wishes of his clients in what he considered to be their most appropriate form.

The Chalet and Stick style of the early cottages, the Italian Villa, the monumental French Renaissance tradition (all reflections of the picturesque High Victorian Gothic of the late ’60s and early ’70s), and finally echoes of the Queen Anne and of the Colonial Revival—all found expression in Lienau’s work.