Hoping for some guidance. I am repiping my heating and wondering if I can safely notch these joists 20mm to allow pipes to sit without significantly weakening them. Floor joists are 4 inches. The joists sit on walls that are too close together to allow me to get pipes under the joists. My other options are go plastic or put short lengths of copper in and solder together as I go. What do the experts think. Many thanks.