Koch designed the house 'Ulimaroa' in the late 1800s for a successful businessman. It was one of many mansions with spacious grounds that were built on the prestigious St Kilda Road. It is historically important as it is one of the few surviving mansions of this type on St Kilda Road and "because of its fine architectural detailing, which is attributed on stylistic grounds to the architect JAB Koch".[1]

A bold expression of the economic success and the boom years of the colony of Victoria in the later years of the 19th century is the Rialto block of office buildings in Collins Street, Melbourne. The Rialto block consists of multiple buildings, designed by various architects.[2] One of those is the four-storey Record Chambers, "adorned with doric pilasters, dentil cornice, panelled frieze, floriated scrolls and caryatids."[3] In 1887 Koch designed this building in Collins Street for the printing and publishing firm of McCarron, Bird & Co., which was an important publisher of insurance and banking journals in Australia.[4]

The first floor of this building was built in 1885 for the German Club, and it included a lecture hall in which people like Ferdinand von Mueller delivered talks. Its facade is a fine example of the Renaissance Revival style. The anti-German atmosphere of the First World War forced the German Club out, and the building was later used by the Naval and Military Club (which was a meeting place for military officers), and still later by a restaurant named 'Mietta’s'. The building is among the small number of surviving 19th century club buildings in Melbourne.[5]

The house `Borussia' in Hawthorn was built in 1879 to the design of J. A. B. Koch for William Alexander Brahe, a well-known lawyer and leader of the German community in Melbourne. Some parts of the house have been changed, but the arcaded single-storey verandah and the semi-circular bay window "display the bold use of architectural elements for decorative effect typical of Koch's work". W A Brahe's house, 'Borussia', was a centre of German cultural and social life in Melbourne from the time of its construction until the strong anti-German atmosphere of World War I suppressed German culture in Australia. The name Borussia is Latin for Prussia.[7]

Perhaps the most famous home designed by Koch is Labassa in Caulfield, owned by the National Trust. Koch was commissioned in 1889-90 to extensively expand and remodel an existing house there and turn it into the thirty-five roomed mansion known today as Labassa. The Victorian Heritage Database describes Labassa as "one of Melbourne's most lavishly decorated nineteenth century mansions" and "the most prominent example of a small number of houses built in Australia in the French Renaissance style. It is of further note due to the German interpretation of the style and the use of Hellenistic sources, via Germany."[8]