I hope somebody can help me with this, my wife has bought a bow fronted bath and wants all the pipework hiding (i.e. under the floor). This means i will have to drill throught the joists. Can somene please tell me if there is a maximum weght a joist will take or how do i calculate it. I have been told the maximum weight of the bath with water is 275Kg and, we also have marble floor tiles which are not light so i'm worried about the joists bowing.