The electromagnetic shielding effect of common building materials is reviewed in order to provide baseline data for computer simulations. The first part of this paper presents the “raw” electromagnetic properties of these materials, like brick, concrete, wood, glass, and a complex material like reinforced concrete with different reinforcement square grid sizes. The second part of the paper presents the effect of the shape of a room made from these materials and the effect of the rounding of corners and window edges on the in-house electromagnetic fields. Simulations are performed with a state-of-the-art computational tool: CST Microwave Studio. It is demonstrated that, apart from slightly focusing the electromagnetic waves to the centre of the room, rounding has a very small effect on the electric and magnetic fields. The last part presents comparative data about different building materials regarding their attenuation and electromagnetic penetration. At the end a carbon foil based shielding technique is described, and the importance of and solutions for window shielding are presented.