Subfloor slopes downward from exterior wall for 2-3ft then levels off...

[andersp]

Hi Folks,

I recently removed all carpets, laminate, etc. in my 35 year old house to expose the subfloor and prepare the house to install hardwood flooring. Along one of my exterior walls, there is a noticeable downward slope away from the wall that extends 2-3 feet (i.e. the width of one sheet of the plywood subfloor). This slope extends across the entire wall of the house. I went to the basement to investigate, and it looks like the main support beam, which is completely level across the entire house, that sits on top of the foundation has settled over time. The reason I assume it has settled is that there is a small gap above the main beam in the concrete foundation where the beam rests. The supporting beam is perpendicular and to the wall in question, and directly in the middle. It seems like the floor joist that is sitting on the foundation has stayed in the same place over time while the rest of the house sunk. It looks, from looking below, like the last two floor joists from the wall have been pulled off the main support beam and are still connected to the subfloor. There is a small gap between the last two floor joists and the main support beam (not including the joist sitting on the foundation). The gap is approximately 1/4" under the first joist off the foundation wall, and 1/8" under the second joist, which explains the slope above. Can I fix this issue without having the raise the main support beam across the entire house? My first reaction was to pull the last sheet of subfloor along the wall and shave the joists to level the floor, but the gap between the joists and the main beam leaves me to wonder if this is the most important issue that needs to be addressed instead.

Thanks in advance!