I'm currently renovating my kitchen, and I removed the tiles and mud bed to reveal a chunk of very rotten subfloor. This section has clearly been replaced before, since it is plywood, and the majority of my subfloor is planks. Replacing it should be easy enough. I'm just planning on replacing the plywood and adding a scab to the joist underneath (there is only a small section where the joist has also rotted, which is pictured), but while I'm here I would like to fix the cause of the leak.
The rotten section is directly under my french door and the deck is on the outside face, so I'm guessing one of these is to blame. Is there some sort of water proofing that I don't have? Thanks in advance!