The principle criteria is based on the "pressure equalized rain screen principle". The basic concept is to create a double skin wall in order to achieve a pressure equalization chamber. The outer skin surface acting as a water and environment deterrent and the inner skin acts an air seal. The effectiveness of the outer skin is greatly improved by being designed to sustain an inward air pressure difference. The pressure difference across the outer skin is practically eliminated by providing adequate pressure equalization openings between the contained air space and the outside, and by assuring a positive air seal of the inner skin.