DIY Crawl Space Supports for Sagging Floors

Doubled Joists

• 1

  Define the floor area that has sagged. Stretching a length of nylon string across the room at floor level is an easy means of determining the extent and depth of the sagging. Measure some reference dimensions to exterior walls to assist in locating the floor area once you're in the crawlspace below.

• 2

  Access the crawlspace beneath the floor area being supported with a light source, builder's level, joist lumber, circular saw and power cord, hydraulic jack, hammer, nylon string, nails and plywood block.

• 3

  Remove any perpendicular joist blocking or bracing from the space beside the joist being doubled.

• 4

  Pull a length of string taut between both ends of the joist being reinforced. Mark the horizontal point where the tightly held string hits the joist mid-span to define where the sag is the greatest, which is generally at the center point. Drive a small nail into the face of the joist near each end to secure the nylon string to as an adjustment guide. A small laser level will also work to define a guideline along the face of the joist.

• 5

  Position the hydraulic jack beneath the maximum sag point marked in the previous step. Seat the jack's base securely on the plywood block and raise the jack post approximately 1-inch above its fully lowered position.

• 6

  Measure the vertical distance between the jack plate and the bottom edge of the joist. Cut a solid 2 by 4 block to this dimension to use as a "jack leg."

• 7

  Position the 2 by 4 jack leg between the jack plate and the joist bottom. Slowly raise the jack until it begins to lift the joist. Confirm that the nylon string guide is tight and unobstructed, or that the laser line is adjusted correctly. Continue to pump the jack arm to slowly raise the sagging joist until the bottom edge aligns with the guideline.

• 8

  Measure the length of the joist being reinforced. The added joist should extend to the nearest girder or foundation support on either side of the depressed floor area to use the same bearing as the existing joist.

• 9

  Cut a length of floor joist lumber to the dimension determined in Step 8 using a circular saw. Take care in the cramped space to hold the material firmly and cut in a safe direction.

• 10

  Slide the new joist into the space next to the existing joist being doubled. Position the ends to extend onto or beyond the support at both ends, then tilt the joist upward into place beside the existing joist. It should be a tight fit and you can use a hammer to push the top edge into place.

• 11

  Secure the two joists together using 16d nails or deck screws spaced about 8- to 10-inches apart and staggered up and down. Add a continuous zigzagged bead of construction adhesive between the joints before fastening into place for an increased support bonding.

• 12

  Release the lift-pressure on the jack to release the jack leg from supporting the joist.

• 13

  Repeat Steps 3 through 12 for additional floor joists being supported. It is common for a depressed area in a floor to involve several of the adjacent joists across a span.

Concrete Pier and Post

• 14

  Define the floor area that has sagged. Follow the procedure described in Step 1 of the previous section. A pier and post support is most effective and appropriate to raising a deflected girder beam that is pulling down a group of joists. Locate the main girder span crossing the sagging floor area.

• 15

  Access the crawlspace beneath the floor area and position the work area at the midspan of the sagging girder. Set up a work area with a light source, a concrete pier, small trowel or short-handled shovel, circular saw and power cord, hydraulic jack, hammer, nylon string, nails and plywood block.

• 16

  Pull a length of string taut between both ends of the girder being supported. Drive a small nail into the bottom edge near each end to secure the nylon string to as an adjustment guide. At the middle of the girder's open span, the sag will be the greatest and this is the support point for the pier and post.

• 17

  Dig a pier footing in the soil below the girder. The footing should be approximately 12-by-12-inches square and at least 3- to 4-inches deep. The footing should be centered under the girder and in the middle of the girder's span.

• 18

  Mix concrete mix following the manufacturer's instructions and fill the pier footing with the wet concrete mixture to just below the ground level.

• 19

  Set a precast concrete pier block onto the footing concrete and press downward slightly to seat the block and level the top block. Use a torpedo level to adjust the pier until the block is level. Let the pier block sit undisturbed for a minimum of 24 hours to allow the concrete to harden.

• 20

  Set up a hydraulic jack on either side of the concrete pier, positioned so that neither the jack base nor the plywood block rests on the pier footing. Seat the jack's base securely on the plywood block and raise the jack post approximately 1 inch above its fully lowered position. On jacks with a threaded rod extender, turn the lift plate counterclockwise to extend the rod about 1 inch.

• 21

  Measure the vertical distance between the jack's push plate and the bottom edge of the joist. Cut a solid 2 by 4 block to this dimension to use as a "jack leg."

• 22

  Position the 2 by 4 jack leg between the jack plate and the joist bottom. Slowly raise the jack until it begins to lift the girder's bottom edge toward the guideline. Confirm that the nylon string line is tight and unobstructed, or that the laser line is adjusted correctly. Continue to pump the jack arm to slowly raise the girder until the bottom edge aligns with the guideline.

• 23

  Measure the vertical distance between the bottom of the girder and top block of the concrete pier.

• 24

  Cut a length of 4 by 4 post lumber to the dimensioned measured in Step 10.

• 25

  Install the post. Slide the cut post into place between the girder and the pier block. You can raise the jack just slightly to ease the post placement. Holding the post in position, release the lift pressure on the jack to allow the girder to rest fully on the post.

• 26

  Secure the post in place using 8d nails driven at angles through the post into the girder and pier block.