The design of Bertram House, methods of construction and use of materials are typical of the Georgian style of town house introduced at the Cape following the First British Occupation in 1795. The significance of some of these features will be examined in more detail.

During the restoration of the house, all the pitched roofing was replaced with Welsh slate in order to conform with the practice adopted by wealthy English residents in 1816. This roofing material proved to be a successful innovation as it was imported ready-cut into five millimetre thick tiles and was light enough to be used on pitched roofs, local Robben Island slate being unsuitable because of its great weight. Welsh slate had the additional advantage of obviating the problems of damp often experienced by flat-roofed houses built at the Cape which were treated with whale oil to make them waterproof.

The distinctive appearance of the symmetrical facade of Bertram House was achieved by importing more expensive but durable face-brick. Locally made bricks were found to be of poor quality, required plastering and had to be lime-washed annually.

The harmonious proportions of the facade are a prelude to the layout of the interior of the house whose rooms are light and spacious as a result of the sash windows characterised by thin glazing bars. These elements are further enhanced by the arrangements of the double drawing room where the Georgian penchant for combining informality with elegance is particularly evident, while the placing of a fireplace in each room is indicative of the Georgian concern for the comfort of the residents.

Although none of the original fireplaces was extant at Bertram House, the museum was fortunate in acquiring seven examples from a contemporary house in Wynberg that had been demolished. A major aspect of the restoration was the woodwork, as all the sash windows and French doors were fitted with internal shutters and external louvred shutters were replaced in keeping with the practice adopted in Cape Town by about 1837.

The original decoration of the walls had not survived but was based on paint scrapings taken throughout each room. A colour scheme was carefully selected and limited to a range of dark greens and ochres.

Attention was given to the treatment of ceilings formed of lath and plaster, often embellished with decorative plaster ceiling roses and cornices. The ceiling rose in the hallway is original, copies were used in the other rooms on the ground floor.
Undoubtedly the finest surviving original feature is the graceful spiral staircase which leads to the first floor with its glazed hexagonal lantern.

The English influence on local architecture during the early years of the 19th century is noted in the accounts of various visitors to the Cape of Good Hope. In September 1800, Robert Semple comments favourably on this factor saying "The English ... are every day improving and beautifying the town". The following description he gives of the interior of a Dutch house illustrates some of the differences between the English style he was accustomed to and that practised by the Dutch inhabitants "... rooms are lofty and not plastered in the ceiling, which particularly strikes the eye of a stranger; the floors are not carpeted, and a few are provided with chimneys". The gradual change of appearance of the town is evident when this account is compared with that made by Andrew Dixon in October 1825. "It is certainly a comfortably laid out place, the houses chiefly composed of brick, limewash'd or otherwise colour’d; are very large and commodious...".