A pier and beam house foundation essentially elevates the house above the ground to provide a level platform based on specifically positioned footings. These footings support wood beams carrying the floor structure and walls above. As a home ages, many factors can contribute to the "sagging" of interior floor areas, such as the natural ground settling at random pier locations. You can level an area of floor using the crawlspace beneath the house.
Establish the area of floor to be leveled and position yourself in the crawlspace beneath that point with a light source, builders level, hydraulic jack, hammer, nylon string, nails and plywood block.
Attach a level string line on the sagging girder beam by tacking a nail diagonally into the lower corner of the beam at two points as near to the ends as possible or, at a minimum, spanning the depressed floor area. Tie a piece of nylon string between the two nails, keeping it taut and positioned visually level with the lower edge of the beam. This string line will define the amount of sag along the length of the girder beam. String lines should be placed on any girder lines that are in the area of the floor to be raised.
Position the hydraulic jack on the plywood block on a flat surface beneath the approximate mid-point of the girder beam to be leveled, next to the nearest pier.
Measure the vertical distance between the string line and the top of each pier block. Ensure that the string line is free and tight. Cut a piece of 4-inch by 4-inch post to replace any existing pier post that that is more that ½-inch shorter than the level string line. New posts are not mandated for a beam sag of ½-inch or less and can be shimmed or blocked between the girder and post.
Use the hydraulic jack set up in Step 5 to raise the girder and remove the existing post or insert the necessary shims to fill the gap. For post replacement, insert the new post in place and lower the girder down to rest on the top of the post. Secure the new post in place with nails diagonally through the side of the girder into the top of the post and at the base of the post into the pier block.
Repeat Steps 3 through 5 at each pier post location that requires leveling according to the string lines. When completed, use a builder's level to check each section of girder to verify level.