I’m rebuilding a house after tearing it down to the bare studs. I found a few spots where (in the bathroom) the floor joist had gotten soaked through and rotted. This is how I fixed them. The house is over a hundred years old, and had surprisingly little rot. This house originally did not HAVE a bathroom attached to it, and the previous owners did a very slapdash job on adding one in. So not only am I dealing with the wear and tear of time, but also shoddy workmanship. Making it so that this house lasts another hundred years is my goal. :)
2 x 6 board. size and length varies
quick setting wood glue
3 1/2" wood screws (length can vary depending on wood size)
flat head screwdriver
electric/ battery operated driver
elbow grease and patience
Find the rotten spots. This can be easy or difficult. You can poke the questionable board with a screwdriver and see if there’s any give to the board, and you can also do a visual inspection: a darker spot on the board can be a sign of rot.