Like I said, there are several contributing factors to the water getting in. I will lay them out now, to get that part out of the way, and then I will proceed with the room build from there. I'm trying to forget about the flooding right now because that's the sour LEMON part!
1) First of all, I have just reached the one year mark in the house, and this has never happened until about 6 weeks ago. We were going through another week of solid rain, and that was the first and last time water came in. That time I just went through the water extraction ritual and dried everything out. This house was one of those cheap fixer-uppers, and I just so happen to love fixing them up!
2) The neighbor to the East of me has no guttering on his house, and it sits less than 20 feet next to mine. When it rains like this, the sheets of rain pour straight off of his roof and property, and come flowing like a river through my backyard. I plan on putting in a french drain system around the house because the neighbor will not put on guttering.
3) When the flooding is this bad, the water is deep and sits against the exterior of the brick/slab foundation. The foundation has either settled and the slab has cracked allowing water to enter, or it is just finding its way in through cracked mortar, etc.
4) There is also some metal flashing on the chimney where it meets the roof that looks like it has been worked on before. The water may be finding its way down there, through the wall, and onto the interior floor.
There are many things to investigate here, in terms of the leaky house, and I will. But as for now, I am going to try not to think about all of that---thus the partial reason for this thread. I just spent the last 9 hours extracting water and temporarily fixing the situation, and now the thunder is rolling in again.
We'll see what happens...