What is the formula for perimeter and area? There are several methods to find area and perimeter, depending on the shape of the figure. To find the area of a square or rectangle, use this formula: length x width. To find the perimeter, use this formula: (length x 2) + (width x 2).What is perimeter insulation? Perimeter Insulation. High quality perimeter insulation can be a vital component in regions where winter temperatures are really going to fall. For subfloor thermal insulation, expanded polystyrene is a rigid foam insulation board that resists moisture penetration and is proven to maintain its R-Value over time.What is a perimeter barrier? Perimeter Barriers. The river level is rising. The water is slowly creeping toward the building. Something must be put in place to stop the water from getting to the building. A temporary perimeter barrier is an emergency structure which, when deployed, is intended to protect an area surrounding an occupancy from rising water.