This work is a research on the application of genetic algorithms (GA) to urban growth taking into account the optimization of solar envelope and sunlight in open spaces.It was considered a typical block of a Spanish grid, which is the most common subdivision of the urban land in towns situated in Argentina. Two models are compared, one in which the growth has no more limitations than building codes. The other one, in which the growth incorporates the solar radiation as a desirable parameter.This way of parameterizing configures a bottom-up method of urban growth. No top-down decisions intervenes in the growth process.This tool proves to be useful at early stages of urban planning when decisions—which will influence along the development of the city for a long time—are taken.