7. Sagging Floors Sagging or sloping floors could be the result of inadequate support beams that are deflecting or failing. Rotted sills or an inadequate foundation are other causes. In addition to affecting the floor, these conditions can cause wall cracks and make doors and windows impossible to open. According to Dr. Sarah Kirby, housing specialist at the North Carolina Cooperative Extension Service in Raleigh, sagging upper floors and those caused by insect or water damage should be looked at by a contractor. You can sometimes correct minor sags on the first floor yourself with a pair of screw-type jack posts and a wood or steel beam to bridge the jacks, but this procedure is difficult and somewhat risky. The posts need a very firm foundation. Even if you have a 4-inch concrete slab, you still need to create a concrete pier pad for the jack that's 18 to 24 inches square and at least 12 inches deep. Once these pier pads have cured and the jacks are in place, begin by raising the floor slowly, as little as a quarter turn per week. Jacking slowly allows for settling without serious disruptions or sudden stress. Lifting might create additional wall cracks and change door and window margins.