The role of courtyard geometry in controlling the seasonal wanning of outdoor space in cold climates is examined. Numerical and physical simulation methods are used to compare the effects of changes to courtyard proportion, configuration and orientation on the key microclimatic parameters of incoming short-wave radiation, outgoing long-wave radiation and wind shelter. Findings are presented in a manner which can easily be integrated into the design process. The degree to which courtyards encourage seasonal warming at high latitudes differs according to their architectural geometry. The importance of each of the courtyard's geometric parameters changes from one form to the next, but a yard's orientation is generally a secondary factor to its proportion and configuration. In many instances, the designer has a fair degree of flexibility in their choice of courtyard form before affecting climate. On the other hand, changes to courtyard geometry need not necessarily be architecturally significant to affect a yard's thermal conditions. Often a number of design options are available.