Courtyard House was designed by Horden in 1974 for his parents, and is the first house he worked on. It is largely based on the work of Craig Ellwood and Case Study Homes seen during Horden's trip to California in 1968. Courtyard House won a RIBA Commendation in 1975.
The building, with its stepped-back brick walls, was one of the most luxurious designs in the Modern style at the time.
Culture Minister David Lammy, said: 'These are both important examples of post-war private homes by two great British architects, which is why it so important to protect them.
'The steel house by Richard Horden is not only a rare example of a steel home in Britain but also an interesting starting point in his career.
'The Camden house by Philip Pank is one of his most luxurious and well-appointed designs and is a rare example of an expensive house in the Modern style.'
Meanwhile, Lammy has announced that he is seeking the public's views on listing Garden Ground in Wiltshire, at Grade II - designed by Robert Townsend in 1953.
It was built as a family home for Townsend, which included a consulting and dispensary room for his general practitioner wife.
Lammy said: 'This is a very unusual house, built by a noted innovator at a time when extremely little private housing was being put up.
'The interior in particular shows very clever handling of space, and this consultation gives everybody the opportunity to comment on the merits of the house before a decision is made.'