משנה: הַנּוֹדֵר מִן הַבַּיִת מוּתָּר בַּעֲלִיָּה דִּבְרֵי רִבִּי מֵאִיר. וַחֲכָמִים אוֹמְרִים עֲלִיָּה בִּכְלָל הַבַּיִת. הַנּוֹדֵר מִן הַעֲלִיָּה מוּתָּר בַּבַּיִת. MISHNAH: One who vows not to use the house is permitted the upper floor, the words of Rebbi Meïr; but the Sages say that the upper floor is part of the house. One who vows not to use the upper floor is permitted the house.
הלכה: הַנּוֹדֵר מִן הַבַּיִת כול׳. נִרְאִין דִּבְרֵי רִבִּי מֵאִיר בְּעִירוֹנִי. HALAKHAH: “One who vows not to use the house,” etc. The opinion of Rebbi Meïr is reasonable for a city dweller47In rabbinic (and also modern) Hebrew, בַּיִת has two different meanings. It may mean “building” in a general sense; but applied to dwellings it usually means “appartment”; in talmudic Hebrew often “ground floor one-room appartment”. In most cases in a city, two different families dwell in the “house”, the ground floor, and in the upper floor. But a farmer uses the ground floor as a dwelling and the upper floor for storage; for him, “house” and upper floor form a unit. Therefore, practice has to follow R. Meïr in a city and the Sages in the countryside.
On the other hand, a mention of the upper floor certainly excludes the ground floor..