The joists of the lower and upper stories of a house have no plaster attached to them and are perfectly aligned one above the other. If there is tumah underneath one of [the joists], [whatever is] beneath it becomes tamei. [If there is tumah] be-tween the lower and upper [joists], whatever is between them becomes tamei. [If there is tumah] above the upper [joist], whatever is directly above it, until the sky, becomes tamei. If the upper [joists] correspond to the space between the lower ones, [and] there is tumah under one [of the joists], whatever is beneath any of them becomes tamei. [If the tumah is] above them, whatever is directly above it, until the sky, be-comes tamei.