Siman 390
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א מָבוֹי שֶׁצִּדּוֹ אֶחָד עַכּוּ"ם וְצִדּוֹ אֶחָד יִשְׂרָאֵל, וּבַיִת שֶׁל יִשְׂרָאֵל אַחֵר אֶצְלוֹ פָּתוּחַ לִרְשׁוּת הָרַבִּים וְלֹא לַמָּבוֹי, וְחַלּוֹן בֵּינוֹ לְבֵין יִשְׂרָאֵל הַדָּר בַּמָּבוֹי, אֵינוֹ יָכוֹל לְעָרֵב דֶּרֶךְ הַחַלּוֹן שֶׁבֵּינֵיהֶם לְהוֹצִיא כֵּלָיו לַמָּבוֹי דֶּרֶךְ בֵּית יִשְׂרָאֵל שְׁכֵנוֹ הַפָּתוּחַ לַמָּבוֹי; אֲבָל אִם פֶּתַח בֵּינֵיהֶם, מֻתָּר. וְיֵשׁ מִי שֶׁאוֹסֵר אַף בְּפֶתַח פָּתוּחַ בֵּינֵיהֶם.
1 An alleyway where one side is a non-Jews and one side is a Jews. Containing 2 paragraphs. An alleyway where one side is owned by a non-Jew and one side by a Jew, and another Jewish house adjacent opens to the public domain but not to the alleyway, and there is a window between him and the Jew living in the alleyway—[the one whose house opens to the public domain] cannot make an eruv through the window between them to carry his utensils into the alleyway via his Jewish neighbor's house which opens to the alleyway. But if there is a doorway between them, it is permitted. And there is one who prohibits even when there is a doorway open between them.
ב מָבוֹי שֶׁצִּדּוֹ אֶחָד עַכּוּ"ם וְצִדּוֹ אֶחָד יִשְׂרָאֵלִים, וְהָיוּ חַלּוֹנוֹת פְּתוּחוֹת מֵחָצֵר לְחָצֵר שֶׁל יִשְׂרָאֵל וְעֵרְבוּ כֻּלָּם דֶּרֶךְ חַלּוֹנוֹת, אַף עַל פִּי שֶׁנַּעֲשׂוּ כְּאַנְשֵׁי בַּיִת אֶחָד וּמֻתָּרִים לְהוֹצִיא וּלְהַכְנִיס דֶּרֶךְ חַלּוֹנוֹת, הֲרֵי אֵלּוּ אֲסוּרִים לְהִשְׁתַּמֵּשׁ בַּמָּבוֹי דֶּרֶךְ פְּתָחִים עַד שֶׁיִּשְׂכְּרוּ מִן הָעַכּוּ"ם.
2 An alleyway where one side is owned by a non-Jew and one side by Jews, and there were windows open from his courtyard to the Jewish courtyard, and they all made an eruv through the windows—even though they became like members of one household and are permitted to carry in and out through the windows, they are prohibited from using the alleyway through their doorways until they rent [the domain] from the non-Jew.