Building Blocks of Halachah

Towards the end of Eiruvin (101a), the Gemara listed numerous examples of this rabbinic restriction. One who is constructing a fire on yom tov may not pile logs on the side and then put logs on top. The top logs would constitute a temporary ohel. One may not construct a bed frame with sides and then put a mattress on top on Shabbos or yom tov. The mattress would be an ohel to the area underneath. One stacking barrels on Shabbos may not stack them in such a way as to create a hollow space underneath. Perhaps the biggest chiddush is that one may not stack eggs if an ohel is created. One may not stack one egg on top of two eggs in such a way that there is a hollow space between the two eggs.

It is clear from the Gemara that the minimum-size roof that needs to be created for an ohel arai is a tefach. A tefach is between three and four inches. The Chazon Ish explains that when the Gemara forbade stacking eggs, it had to be dealing with large eggs. A temporary ohel of Magna-Tiles that has a four-inch square as a top and is four inches tall can run afoul of these restrictions. A small square Magna-Tile is a two-inch square. The larger ones are four-inch squares. If the roof is a solitary two-inch-square Magna-Tile, then there certainly is no problem.

The aforementioned cases from the Gemara are all codified as practical halachah. Therefore, when one argues that a Magna-Tile house is flimsy and cannot possibly be considered a temporary ohel, the response should be that even stacked eggs are a problem.

Tosfos mentions some leniencies in regard to this halachah. Standard ovens in the times of the Tosfos and the Gemara looked like a box with a hole on top for placement of a pot. Firewood was put in the earthenware box, and the heat escaped through the hole on top where the pot would be placed. Tosfos says it is well-known that it is permitted to place the pot on top of the oven on yom tov (even on Shabbos it is allowed under certain circumstances). This is true despite the fact that an ohel is seemingly created by the pot, which can be viewed as the roof of the oven. Tosfos therefore opines that the issue is limited to a situation where one is constructing the walls and the roof on Shabbos or yom tov. Since the walls of the oven existed before Shabbos and yom tov, the prohibition of a temporary ohel doesn’t come into play.

This doesn’t help the issue of Magna-Tiles because one is making the walls and the roof on Shabbos. Tosfos continues that everyone stacks challah rolls and sefarim on Shabbos. Does one really have to ensure that no hollow space is created when he stacks these items? Tosfos offers two reasons why the issue of ohel arai won’t apply in those cases. Tosfos suggests that building on a tabletop would be permitted. However, that suggestion is not mentioned by the Rema or the Mishnah Berurah. Additionally, it is only when one wants to use the space created by the ohel that there is an issue. When one stacks sefarim and rolls, he couldn’t care less if there is an ohel created or not. It is only when one wants to use the newly formed ohel or hollow area that there is a problem. One must conclude, therefore, that in all the situations mentioned in the Gemara, one wanted the ohel. When one was stacking the barrels and the eggs, he wanted the airflow to keep them from getting ruined. When the bed was made, he planned on keeping things under the bed. When one stacked the logs, the hollow area provided oxygen to fuel the fire.

The Rema codifies this explanation of Tosfos. Therefore, it can be suggested that Magna-Tiles are only an issue if one plans on using the inside of the structure for toy men, cars, dolls, or the like. If one is building a beautiful palace and doesn’t need the hollow space that is created, Tosfos and the Rema would say that it is permitted.

Someone may suggest that one could use the Magna-Tile pieces that are just a frame but hollow in the center. After all, in this situation the ceiling of the Magna-Tiles won’t have a contiguous tefach of tile. However, this argument fails. Based on the Gemara and halachah, it seems that as long as the various segments are within three tefachim of each other, they are halachically considered one united piece. This is a manifestation of the concept of lavud. (A fuller analysis of lavud is beyond the scope of this article.)

The Gemara offers a way to construct a temporary ohel, and that is to put the ceiling in place first. If one wanted to do this with Magna-Tiles, one would hold the ceiling tile in place and then put the walls in position. In this way, one would even be able to use the insides of the Magna-Tile structure.

HaRav Shlomo Miller, shlita, was quoted as permitting one to play with Magna-Tiles, but it’s not clear if he permitted them even when intending to use the inside of the structure or just building a structure.