1. The Principle of Lavud in Sukkah Walls
The halacha of lavud—gaps less than three tfachim (handbreadths) being considered closed—is foundational for constructing Sukkah walls. The Shulchan Aruch brings that if you make a strip around four posts at the bottom, then another strip less than three tfachim above it, and continue this pattern, the gaps between the strips are considered connected due to halacha l’Moshe miSinai—a tradition from Sinai. Even though you technically don’t have a solid wall of ten tfachim, since each strip is within three tfachim of the next, we combine them and consider it as if there is a full wall. This creates a kosher Sukkah wall, as long as the total height reaches ten tfachim.2. Gud Achis Mechitza: Extending Walls Upward
Another important rule is gud achis mechitza—we view a wall as if it extends upward to the top of the Sukkah, even if it physically stops at ten tfachim. For example, if you have a regular solid wall that is ten tfachim high (about 40 inches), halacha allows us to consider that wall as reaching all the way up to the s’chach—the roof covering—even if there is space above it. This too is based on halacha l’Moshe miSinai. However, this only applies if the wall comes right up to or even slightly into the area under the s’chach. If there is a gap of three tfachim or more between the top of the wall and the start of the s’chach, then that wall does not count for your Sukkah.3. Ideal Versus Minimum Wall Construction
While these leniencies exist, ideally (l’chatchila) one should build solid walls for their Sukkah. The reason is that a Sukkah should resemble a home—teshvu k’ein taduru, “you shall dwell as you live.” Solid walls provide privacy and usability similar to an ordinary dwelling. If your walls are just strips or have many holes, everyone can see inside, which does not fully meet this ideal. Although such a structure may technically be kosher due to these halachos, it’s preferable to build proper walls like those in your house.4. Are Walls with Holes Considered Valid?
A question arises regarding whether a wall with many holes can be considered a valid wall on its own, or only because we apply the rule of lavud. If most of what stands is holes rather than solid material (porutz merubeh al ha’omed)—more open than closed—then perhaps we need to rely on lavud. There’s uncertainty whether such a perforated structure counts as a true wall without invoking this special rule.5. Combining Multiple Halacha l’Moshe miSinai Principles: The Machlokes
This leads to an important dispute: Can you use two different applications of halacha l’Moshe miSinai together for one wall? For example, suppose you construct your ten tfachim-high “wall” using strips and rely on lavud. Then you want to use another principle—gud achis mechitza—to extend that “wall” up to the roof. Rav Akiva Eiger rules that you cannot “double dip” by combining two such traditions for one wall: either you use one or the other, but not both together for a single halachic outcome. Other poskim disagree and allow combining them in certain cases. However, out of concern for this issue, we rule practically (L’Poel Mamesh) that it’s best to cover your Sukkah walls all the way up to the roof so you don’t enter into any doubt about their validity.6. When Two Halacha l’Moshe miSinai Rules Are Permitted Together
There are situations where even Rav Akiva Eiger would agree that two different applications are allowed—if they serve separate functions. For instance, if one application of halacha l’Moshe miSinai, such as lavud, creates your actual wall structure, and another application connects your roof (s’chach) with that wall (e.g., filling in a gap so there isn’t three tfachim between them), then both can be used since each addresses a distinct aspect of Sukkah construction. But when both rules are needed just to create one kosher wall (e.g., using both lavud and gud achis mechitza for height), Rav Akiva Eiger says this is not permitted.7. Practical Guidance for Building Sukkah Walls
If you have an ordinary solid wall that doesn’t reach all the way up to your roof but stands at least ten tfachim, then applying just one principle—gud achis mechitza—is straightforwardly acceptable according to all opinions. However, if your “wall” only reaches ten tfachim by relying on lavud (strips within three tfachim), then adding gud achis mechitza on top becomes problematic according to Rav Akiva Eiger. That’s why in practice we ensure our walls go all the way up—to avoid relying on multiple leniencies for one requirement. If someone argues that their perforated structure counts as an ordinary mechitza regardless, perhaps they wouldn’t need these stringencies at all—but I am not convinced this is correct. Therefore, we maintain our practice of building continuous walls up to the s’chach for certainty in fulfilling this mitzvah properly.