Thermal conductivity is an important parameter in the designing of the energy-efficient building envelopes. Thus, with the growing awareness of low energy buildings, there is a need for an optimized method to estimate an effective thermal conductivity of building materials accurately. In this work, two- dimensional (2D) and three-dimensional (3D) semi-analytical models are proposed to estimate an effective thermal conductivity of two-phase building materials with spherical inclusions. The proposed semi-analytical approach is based on the formulation and the solution of a boundary value problem. The 2D model is simple and limited in scope, while the 3D model is widely applicable and is based on a multipole expansion method. The 3D model incorporates secondary parameters like size distribution, variation in thermal conductivity among the inclusions, particle interaction and statistical spatial distribution. For the 3D model, spherical representative unit cells (SRUC) based on the face-centered cubic arrangement and trimmed spheres at the boundary are proposed for uniform size distribution and constant thermal conductivity among inclusions. SRUC based on the random distribution of inclusions has been used for inclusions with non-uniform size distribution. Effective thermal conductivity estimated by the proposed models is compared and validated with experimental results from the literature. The 2D model predicts a thermal conductivity of conventional concrete with reasonable accuracy where the relative error is less than 12%. The 3D model predicts accurate results for foam concrete with a relative error of less than 15%. Predictions of thermal conductivity of lightweight concrete by the 3D model are also in good agreement with experimental results. The 3D model is further extended to incorporate the effect of imperfect interface between inclusion and the matrix and has shown good results for conventional concrete with an error of 5%. Thus, flexibility with SRUC and incorporation of particle interactions make this 3D model widely applicable for building materials with spherical inclusions.