When the mat is cast next to an existing building, a continuous layer of polystyrene 1 to 2 in. thick must be placed to prevent the adhesion that may lead to additional interference between the two foundations.
Although it is not always necessary to strengthen the mat edges, we recommend that an embedded beam with stirrups be provided. The stirrups play an important role against the possible punching shear that the columns could originate and also help support the top layer of reinforcement.
For mats with a depth < 16 in., the width A of the edge beam will be A = H. For higher values, A >= 16 in.