If you can open and close your bedroom door with ease one day but the next day it sticks, your house may be settling and shifting. Some foundation movement is unavoidable as the soil under it moves. In addition to ground movement, other factors can cause foundation shifting. You can reduce minor shifting with some preventative measures, but if there's a structural problem your foundation might require professional attention.
Signs of Shifting
Foundation shifting affects more than just the floors, although one of the first signs may be a new squeak when you walk across a certain section of the floor, or splits in the seams of a hardwood floor. In addition to door bottoms rubbing the floor, check the walls for signs of cracking, which usually occurs above doors and windows. If the exterior of your home is brick, you might find cracks in the mortar that follow a stair-step pattern.
Saturated soil swells, which creates pressure on the foundation walls, eventually causing them to move. When the foundation moves, everything attached to it shifts. Directly above the foundation is the sill plate that supports the floor joists and the wall framing, so even small foundation movement can affect other areas in the home. While moisture is the most likely cause of the movement, it's not the only one. Faulty workmanship, including inadequate steel reinforcement or non-compacted soil can result in movement.
Minor repairs include sawing or planing the bottom of sticking doors to allow them to open and close freely and filling wall cracks with joint compound. If the foundation has a structural problem, it may require the installation of steel I-beams to stabilize the inside basement walls. Alternately, repairs can be made to the exterior of the foundation by excavating and installing concrete or steel anchors to stop outward movement. Excavation and structural repairs are best left to the pros.
Keeping water away from the outside of your foundation is critical. Install roof guttering and downspouts and transplant bushes and other plants that require watering away from the foundation. The grade of your yard should slope downward and away from the foundation to encourage rain to drain away from the house.