The logic of the san phra phum begins with an acknowledgment: the ground a house stands on already had an occupant. The guardian spirit of the plot, the phra phum or chao thi, must be housed honorably or the household risks misfortune, and so a dwelling is built for it, raised on a pillar to eye level or above, in the form of a miniature temple or traditional house. Figures of the guardian and attendants stand inside; offerings of rice, sweets, water, red soft drinks, flower garlands and incense are set on its platform, most carefully when something in the household is changing. Installation is a rite in itself. A specialist determines the auspicious position, classically a spot the shadow of the main building will never touch, and the auspicious day and hour for raising the post. If the plot changes, the spirit house may need to be moved or replaced, and retired spirit houses are not discarded casually: they accumulate at temple walls and sacred trees, left where the displaced spirits will be safe.
The practice sits comfortably beside Theravada Buddhism without being of it; monks may be invited to chant at a blessing, but the spirit house belongs to an older stratum of the religion of place. Anthropologists of Thai religion treat it as a standing negotiation between the household and the unseen owners of the land it occupies.