Before I bought this place I knew the porch was unsafe to walk on, I had to lay plywood down over the floor just to be able to walk across it until I had time to get to this problem, I needed water to the main house shower and toilet first.
After a couple weeks I removed the porch flooring strips and found joists that had fallen down due to rot and rusted through nails, the joists were no longer supporting the floor above, that said this was not too bad of a repair, I used a bottle jack to hold the joists up and installed exterior grade screws . One joist had some rot at the end so I sister it as seen in photo.
While I was down there making repairs I found the dryer was venting into the crawl space, this is never a good practice as it adds moisture to the crawl, the last pictures show the porch back together and the new dryer vent running to the outside.
looks like it was not too bad of a fix, unless the top boards were over nailed