Since the sukka is a temporary residence, living in it will naturally not be as comfortable as living at home. Indeed, this is the mitzva – to reside in a temporary residence for the week of Sukkot. Therefore, we are not commanded to build impermeable, insulated, thick walls and sekhakh to protect its residents from cold, heat, and rain (as we would do in our normal homes). As a result, sometimes being in the sukka entails discomfort, in which case one is exempt, for one who is experiencing discomfort (a “mitzta’er”) is exempt from the mitzva of sukka (3:8-10 below). Thus, when it is very hot, or during very cold nights, or when it is raining, one is exempt from sitting in the sukka. A sick person for whom sitting in the sukka causes discomfort is exempt from sitting in the sukka and has no obligation to build a spacious, robust sukka so that he can remain there while experiencing the comforts of home (Maharaḥ Or Zaru’a §194).
However, one who was lax about building his sukka, so that he experiences discomfort in it even in normal weather, has not fulfilled the mitzva; it has become clear in hindsight that he failed to build a sukka that is worthy as a temporary residence, for even under normal conditions he experiences discomfort in it. One who knows that he can stay in a small, rickety sukka without experiencing discomfort may build such a sukka and fulfill the mitzva, as long as he resolves not to claim in the middle of Sukkot that he is mitzta’er because the sukka is too small or rickety. (See Bikurei Yaakov 640:13; MB 640:24.)
According to many, if one built a sukka that is not fit to sleep in – for instance, if it is in a windy place, and he built walls made of screens, so the wind and cold penetrate – then the sukka is invalid for eating as well. Likewise, if he built the sukka in a bad neighborhood where criminals roam around at night, making it dangerous to sleep there, then the sukka is invalid for eating as well. This is because the mitzva is to build a sukka that will serve as a temporary residence, for eating and sleeping, and since his sukka is not fit for sleeping, it is not considered a residence, so it is invalid for eating as well (Yere’im; Rema 640:4). Others say that even a sukka unfit for sleeping is kosher for eating; even though he sinned by building a sukka unfit for sleeping, since it is fit for eating in, it can be used to fulfill the mitzva of eating in the sukka (Ḥakham Tzvi). If one builds a normal sukka that is fit for sleeping in Eretz Yisrael, but he cannot sleep there because he lives in a cold climate, all agree that it is kosher, as the Torah does not obligate us to build a permanent structure as a sukka. (See MB 640:18.)
If one lives in a place where building a sukka would require his investing major efforts or a great deal of money, he must invest in the sukka to a degree comparable with what he would spend to arrange nice living quarters for a week. That is, he should think to himself: “If I had to leave home for a week, how much trouble would I go to, and how much money would I spend, to arrange comfortable lodgings?” That is how much he must invest in building a sukka or getting to somewhere he can build a sukka. One who periodically takes vacations must invest, in building a sukka or renting a place where he can access or build one, the amount he would pay for a week’s vacation, each person in accordance with his financial situation.
When one buys a home, he should make sure that it has a place to build a sukka. He should spend on this however much one who has to leave his house for one week a year would spend to ensure he could live in comfort for that week each year. A wealthy person must spend whatever he would be prepared to spend on a week’s vacation every year over many years.[20]
