Wikipedia
("house-protector", an inflected compound of vāstos, the genitive of vāstu "house", and pati "lord") is a Rigvedic deity that presides over the foundation of a house or homestead, addressed in RV 7.55. Some claim it to be another name for Rudra, an avatar of Shiva. In modern-day Hinduism, he is regarded as the lord and protector of the household.
Vāstu means the site for building and also the house. Hence vāstu pūjā means the worship of the site chosen for building a temple or a house. It is treated as a must for safe and sound construction.
Vāstu pūjā (worship of the site)+ Which destroys obstacles in the building of homes. Beginning from the North-East corner the worship shall extend to eight-one feet in the South-West. The twenty-two deities shall be worshipped outside the plot and thirteen within. ( Garuda Purana- Vāstu-pūjā)
Vāstu-purusa is the presiding deity of the site. According to legend in the Matsya-purāna, Lord Shiva assumed a ferocious form to kill the demon Andhaka. Drops of perspiration fell from Shiva's forehead and therefrom a fierce ghost came out. He was given a boon by Shiva. Thereafter he fell down covering the entire earth. Then he came to be worshipped. In Vedic literature, we come across Vāstospati, the Protector of House.