1,231. Building a Fence on One's Roof

190:1 There is an obligation for one to make a parapet on his roof as per Exodus 22:8, "build a parapet for your roof." The height of the parapet must be at least ten handbreadths high and it must be strong enough so that a person can lean against it without falling. This only applies to roofs that are used (like those on apartment buildings). Roofs that are not used (like those on modern houses) do not require parapets. It's not just a roof that requires a parapet; anything that poses a danger where a person could have an accident and die requires a parapet and/or repair. If one leaves it without a parapet, he fails to fulfill a positive mitzvah and he violates a prohibition, namely Deuteronomy 22:8, "do not bring blood upon you house." For example, if one has a pit in his courtyard, he is required to surround it with a barrier ten handbreadths high or to cover it so that no one will fall in.

190:2 Similarly, one must safeguard or remove any potentially life-threatening hazard as per Deuteronomy 4:9, "take heed and protect your life well." If one neglected a hazard and did not remove it, he fails to fulfill a positive mitzvah and he violates the prohibition against bringing blood into one's house. Examples of such hazards include leaving a broken ladder in one's house or yard, and raising a vicious dog.