Daf Yomi - Moed Katan 11 - Mitzva of Constructing a Maakeh

The Mishna states: One is permitted to build a fence (maakeh) for a roof or a porch, provided that it is done in an amateur fashion.

The Ritva states that our Mishna is not referring to the mitzva of maakeh since a porch is exempt from the obligation of constructing a maakeh. Furthermore, if there would be a mitzva, he should be permitted to build a maakeh using a professional.

The Gemora in Sukkah (3a) states that if one has a house that is less than four amos squared, he is exempt from building a fence around the roof, for this is not considered a house. The commentators ask that it is still a stumbling block and if one doesn't build a fence there, it will endanger people's lives? The Gemora in Bava Kamma (15b) learns from the passuk of lo sasim damim beveisecha that one should not raise a wild dog in his house or a rickety ladder. Shouldn't he be required to build a fence here because of the possibility of someone falling?

The Chazon Ish (Y”D 214) answers that in truth a roof is not a dangerous area and it is not considered a stumbling block. People who ascend a roof understand beforehand that they must be careful and this is a worldly custom. The Torah, nevertheless mandated that one who builds a house is required to build a fence on the roof and this halacha has its guidelines. A house that is less than four amos squared is not regarded as a house for this halacha.

The Emek Brocha adds that this explains why one is not allowed to build a professional maakeh on Chol Hamoed even though he would be permitted to build and fix other things for the fear of bandits. The lack of a maakeh is not an inherent danger and therefore is not considered a dovor heovud, an irretrievable loss and will not be allowed to build on Chol Hamoed. (This is not like the Ritva we mentioned above.)

Reb Akiva Eiger asks on the obligation to recite a blessing when building a maakeh. Tosfos in Chulin (105a) rules that one does not recite a blessing on mayim acaharonim (water after the meal) for it was instituted for the benefit of man that he shouldn't harm himself due to the melach sdomis (certain type of poisonous salt). It would stand to reason that constructing a maakeh should not have a blessing either, for it is only to prevent damage? Rabbi Dovid Goldberg answers according to the Chazon Ish: A maakeh is not built to prevent damage. In truth, it would not be necessary; the Torah taught us that it is required even if it is merely a distant possibility for a damage occurring, hence a blessing is recited.