Howard Wolfe asked:
When the Gem. talks about a house less than 10 tefachim high, which is completed by the roof, why doesn't it mention that a roof on which you can walk must have a fence, which would change its status to Birshus Hayachid?
The Kollel replies:
Sharp question. Why does the Gemara say that it is permitted to carry on top of the roof because the walls of the house are 10 Tefachim high -- even if the walls are not 10 Tefachim high, the roof has a fence 10 Tefachim high around it (because of the law of Ma'akah) which makes it into a Reshus ha'Yachid!
The Gemara is obviously talking about a roof that does not have a Ma'akah. Perhaps it is the house of a gentile, or Hefker (ownerless), or perhaps the owner has not yet built his Ma'akah.