Little is known about Douglas's private life and personality. Only two images of him are known to survive. One is a photograph taken in later middle age. The other is a caricature sketch made by an assistant in his office. This shows him in old age, bowed, bent and bespectacled, carrying a portfolio and an ear trumpet. According to architectural historian Edward Hubbard, Douglas's life "seems to have been one of thorough devotion to architecture ... which may well have been intensified by the death of his wife and other domestic worries". His obituary in the "Chester Chronicle" stated that he "lived heart and soul in his profession".