The purpose of this study is to define the protection against electromagnetic pulses (EMP's) provided by reinforced-concrete buildings. We want to define the electromagnetic field inside a building modeled by parallel wires because attenuation due to concrete itself can generally be neglected. The problem resolution is achieved by using integral equations in the time domain. These equations are solved numerically by applying the method of moments associated with the utilization of Lagrange interpolation polynomials. Applications in the field of building protection are shown.