Vastu is a science, it's not based on religious scriptures.
Vastu's origin is in Vedic times and it is the traditional Indian system of architecture and design. Vastu means the dwelling of humans and Gods. Many Vastu rules are derived from 'Vastu Purusha Mandala' which is depicted as a man lying with his head pointing north east, in a grid of usually 64 squares. The different directions and sectors are assigned to different Gods and Guardians. It aims at providing guidelines for proper construction. Vastu gives orientations, places and dictates the proportions of every detail in building lines, skylines, elongations (Elongation is the angle between the sun and a planet as seen by an observer on earth), levels, slopes, water (underground and overhead), kitchen, bedrooms, toilets, staircase, heights of ceilings and roofs, entrances, doors and windows, compound walls and so on. Vastu is affected with positive power of three elements: the earth, the water, the sun (Fire).
It is true that over the years Vastu Shastra has imbibed religious overtones, but that does not seem to have been the original idea. The religious implications were probably inculcated by the proponents of the science, when they realized that the society of that time, being a God-fearing one, would not accept norms that strayed away from the notions of God.
Religious icons have no place in science and Vastu. The ancient text of Vastu did mention various Gods from Hindu mythology fixing their locations on the site and prescribing the offerings to be made to them, but that also seems to have been a metaphor to represent a basic element in that direction.