In the mid 19^th century and in the beginning of the 20^th century, windows and window frames were not only a functional detail of residential architecture but also determined the aesthetic aspect of the facade. The layout of windows and window frames had an important impact upon the composition and stylish character of the elevation in the period of historism, Art Nouveau and early modernism. The article addresses technical and technological issues (construction and material) of window woodwork, composition related and aesthetical aspects of layout and decorative form of windows, their divisions, window frames and colours.

The research demonstrated that in the second half of the 19^th century and in the beginning of the 20^th century, windows with window frames were used in Warsaw tenement houses (double windows with eternal wings opening outwards). Casement windows and semi-casement windows (double with all wings opening inwards) started to be used from the mid of the first decade of the 20^th century.

The following solutions were used in reference to window construction and division in various periods: two-wing double windows, double windows divided into two parts with transom windows, double windows divided into three or four parts with transom windows and other specialised solutions (e.g. shop windows).

The article discusses dominating trends of window layout evolving in line with the style and colour of window woodwork. In Warsaw, until approximately 1910, the outside parts of the windows were painted with dark colours. Then white started to become popular. Currently, the reality in reference to colours and materials in preserved tenement houses frequently departs from the original, due to changes in use and reconstruction after war damages. The recognition of the original state and arrangement of solution into chronological order is important for correct design of the current construction, conservation and modernisation works of the historical building substance.