Can you put a mezuzah on someone else's home without permission?

Question

Can you put a mezuzah up on someone else's home without permission?

Answer 1

Firstly, I'm not sure why you would want to do that.

We learn the following in the Gemara (פסחים ד' ע"א, בבא מציעא ק"א ע"ב, עבודה זרה כ"א ע"א) and it's codified by the Rambam (Mezuza 5:11): שֶׁהַמְּזוּזָה חוֹבַת הַדָּר הִיא — the obligation to affix a Mezuza falls on the occupants, and not on the building.

In other words, the person living there has a Mitzva to affix the Mezuza. There's no obligation for the house to have a Mezuza. Instead, there's a Mitzva for the inhabitant to affix a Mezuza on their own house.

So you may not be achieving anything, Mitzva-wise, by putting a Mezuzah up on someone else's home without permission.

Secondly, there's a problem of damaging other people's property, which is forbidden. So, unless you can affix that Mezuza without damaging the doorpost (no holes, no glue, etc.) you'll be responsible for damages.

By the way: One is also forbidden from causing damage with the intent of paying for the damage.

In conclusion: You may do more harm than good, Mitzva-wise, by putting a Mezuzah up on someone else's home without permission.

Answer 2

I am not paskening anything here, please ask LOR for Halacha Lemaseh.

Just as @IsraeliReader commented above, I believe that one can put a mezuzah on someone else's door if someone wants. We can say this since we can apply the concept of זכין לאדם שלא בפניו- one may act in someone's favor in their absence. This comes up in a few places in Shas including Ketuvot 11a, Kidushin 23a, Bava Metzia 12a, and Chullin 83a.

The Achronim discuss how זכין לאדם works: According to Rashi Gittin 9b, Ra'an Nedarim 36b ד״ה איבעיא, Tosfoat Pesachim 91b ד״ה איש, Rosh Kidushin 2:6, Shiurei Rebbi Shmuel Bava Metzia חלק א עמו קמג, and many more, זכין לאדם works based on shelichut, and the shelichut even works when the person is not aware of it. This is based on שלוחו של אדם כמותו which appears in Chagigah 10b, Nedarim 72b, Kidushin 42, etc. It's important that according to the (מהרחשת (חלק ב כז-א-ו even those who say that זכין לאדם does not work through shelichut they admit/agree that shelichut is involved to make it work but that זכין לאדם can also work without שליחות like by a Kattan.

Therefore according to the many sources cited above, you would actually be making the person without the mezuzah merit doing a mitzvah deoritah midin shelichut!

There is another point we also need to address which is how we define זכין, does it follow what the individual person wants, or what everyone else wants? There are many cases discussed in the Rishonim and Achronim but perhaps there is one case (in my opinion) that mezuzah is similar to:

The case is if a Jewish housekeeper takes challah from the dough of the home owner without permission- which is basically taking money out from the bal habyit. The Terumat hadeshen (188) says that we apply זכין לאדם, however, the Ketzot Hachoshen (243-8) explains in the opinion of the Rashba and Tosfoat (Nedarim 36b) that in this case, we don't apply זכין לאדם. However many Achornim understood that the Rashba does apply זכין לאדם here, including: Rav Shimon Shkop Kidushin 19, Brit Avraham Even Haezer 101-9, Imrei Bina Terumot 6, Chazon Ish Even Haezer 49, Oneg Yom Tov 107, and the Birkat Shmuel Kidushin 19.

So perhaps this case is similar to mezuzah, since just as the housekeeper took off chalah which is taking out money (מוציא ממון) without permission for the purpose of a mitzvah and is also part of the mitzvah, so too by mezuzah the person placing the mezuzah also takes out money (maybe causes minor damage) without permission for the purpose of the mitzvah and is also part of the way the mitzvah is done.

Also see the Ra'an Gittin 19b and the Sdei Chemed (חלק ב ד-כב עמוד 356) which talks about another case of זכין לאדם with a loss of money.