A computational study of buoyant flow in a roof of triangular cross-section has been carried out for the two-dimensional laminar natural convection under winter day boundary conditions. Stream function-vorticity formulation cooperated with control volume integration solution technique is adopted in this study. Steady-state solutions have been obtained for Rayleigh number ranging from 10(3) to 10(6). The effects of height-base ratio and Rayleigh number on the flow structure and heat transfer are investigated. The results show that height-base ratio and Rayleigh number have a profound influence on the temperature and flow field. As the Rayleigh number is increased, a multiple cell solution is developed between hypotenuse and base wall. The transition to the multiple cell solution depends on the Rayleigh number and height-base ratio. The results of heat transfer are also presented.