In this work, numerical analysis of steady laminar natural convection in a roof with an isosceles triangular cross section has been performed for wintertime conditions. Base angles varying from 15 degrees to 75 degrees, that is, with corresponding aspect ratios between 0.13 and 1.87, have been used for Rayleigh numbers ranging from 103 to 105. The inclined and the base walls are maintained at cold and hot, respectively, representing the wintertime conditions. To perform the computational analysis, the finite-volume method is used for the discretization of the governing equations. The effects of the Rayleigh number and base angle on the flow field and heat transfer are analyzed. The detailed streamline patterns and temperature distributions are presented. The variation in the average convective Nusselt numbers versus Rayleigh numbers and base angles is given. The present study aims to help designers and builders to select the most suitable isosceles triangular roof base angle from an energy-saving point of view. It is found that roofs having low base angles are not suitable for wintertime conditions because of high heat transfer rates from the isosceles triangular attic space of the building.