There is a seam that changes width in the middle of my hardwood floors. In the summer, the seam is at its smallest 1/16th inch as the heat causes the planks to swell. In the winter, the seam widens to up to 1/4 inch as the wood shrinks. This is the only seam that changes. I found out that directly under this seam, is a metal i-beam to support the load. To the left of the crack, is what use to be a proch that they later encloded to make it into this one large room, to the right is the original room. On the left, they apparently rebuilt the porch before enclosing it because i see they used plywood subfloor. On the right of course is the existing subfloor which look to be tongue and groove planks of wood. I assume the gap is happening because of 2 different subfloor materials that are expanding/contracting at different rates and /or not properly joined during the remodel. On the surface above, is there maybe a way to fill that gap with some kind of material to allow its natural movement but not have a crack in the middle of my floor?