Answer
(Fatwa: 934/520/D=1432)
If the safs (rows) keep on increasing continuously outside the mosque and reach to a house, then the people of that house can join the jama’ah and offer salah. But, if there was any street or road in between which was free from namazis, then due to missing the link of saf (row), salah shall not be valid in the house. The link of saf from one floor to another floor is found; hence performing salah at second floor shall be valid provided they are aware of Imam’s activity.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband