A battlement, i.e. a fence or breastwork, because the roofs of their houses were made flat or plain, that men might walk on them. See Judges 16:27 1 Samuel 9:25 2 Samuel 11:2 Nehemiah 8:16 Matthew 10:27. Blood, i.e. the guilt of blood, by a man's fall from the top of thy house, through thy neglect of this necessary provision.
Related Commentaries of Deuteronomy 22:8
Deuteronomy 22:8
8 When thou buildest a new house, then thou shalt make a battlement for thy roof, that thou bring not blood upon thine house, if any man fall from thence.