<p>In this paper, we study a two-scale parabolic problem describing water-induced swelling in porous materials. Our problem consists of a parabolic equation describing the diffusion of the moisture content in a macroscopic domain and a free boundary problem capturing microscopic swelling in individual pores. The macroscopic domain is a bounded three-dimensional domain occupied by the material, while the microscopic domains are each pore modeled as one-dimensional halflines with one endpoint connected to the macroscopic domain. By imposing a flux boundary condition at the edge of each pore, we allow the moisture content to penetrate into the respective microscopic domain. In this work, we prove the existence and uniqueness of a strong solution to our problem. One key to our proof lies in deriving a uniform estimate for solutions to a suitably constructed approximation problem and the continuous dependence of solutions. Based on these results, we construct a locally-in-time strong solution to our problem by the limiting procedure with respect to the approximation parameter.</p>