The area of any sign shall be computed as the total square foot content of the background upon which the lettering, illustration or display is presented, including in such background, any decorative motif or moldings and also including any enclosed open space, such as space between name panels or open space which is part of an ornamental design. Where a sign has a double face, only one side of the sign will be used when computing the total square footage of the sign. If the lettering, illustration or display is not affixed to a background but is affixed directly to the wall of a building or other structure, the area of a sign shall be computed as the product of the largest horizontal distance and the largest vertical distance of the lettering, illustration or display. The supporting members of any sign, which are used exclusively for such purpose, shall not be included in the computation of the area of the sign. Window signs shall not be included in calculating the total sign area of a building. The sign height of freestanding signs shall be limited to 10 feet.