Last Mishna in Shabbos, if there is one tefach break in the vat on top of the 2 roofs, the tumah does not spread....my grandson asked why does'nt Lovud (a break less than 3 tefochim is not considered a break) apply and therefore even if there is one tefach the tumah should travel since Lovud says that the 2 parts of the vat on top are now considered connected?

Kesiva VaChasima Tova