How to Install I-Beams on a Bowed Basement Wall
Clay-based soil, lack of steel reinforcement or soil expansion caused by alternating freeze/thaw cycles, can all contribute to a bowed basement wall. As the lateral force of the soil outside the basement wall increases, the wall reacts by moving in the only available direction – inward. This results in bowing and cracking. Installing I-beams can stop the inward movement, but you must make provisions to support the floor joists when you install them. While this method is straightforward, consult a structural engineer before you begin to ensure you’ve protected the joists adequately.
Hold a plumb bob string on the underside of the subfloor, between the floor joists and directly above the greatest protrusion in the bowed wall. The string of the plumb bob should come within 1/16th of an inch of touching the wall. When the string is in the right spot, make a mark on the basement floor and another one on the underside of the subfloor. These are the upper and lower guides for installing the beam.
Draw a 2-by-2-foot square around the lower guide mark on the concrete floor with a measuring tape and a pencil.
Cut along the perimeter of the square with a concrete saw, and then break out the rest of the concrete inside the square with an electrical jackhammer.
Remove the chunks of broken concrete from the hole and use a shovel to dig the hole to a depth of 8 inches.
Position a standard 2-by-8-by-16-inch patio brick in the hole, with the brick centered beneath the plumb bob mark you made on the underside of the subfloor.
Measure from the top of the patio brick to the subfloor and subtract 1 inch. This is the length your I-beam must be. A metal supplier or fabricator can cut a steel I-beam to match this measurement.
Support the Joists
Cut boards of the same dimension as the existing joists to make the joist blocks. If the joists run parallel to the wall you’re fixing, you’ll measure and cut a block to fit perpendicularly between each of the joist spaces all the way to the other side of the basement.
Measure each joist space separately when cutting the blocks. Standard joists are on 16-inch centers, which leaves about 14 1/2 inches between joists, but there may be slight discrepancies, so measure every space.
Install one block, sideways, in each joist space, starting at the joist space next to the plumb bob mark and adding additional blocks in each joist space until you reach the other side of the basement. Use a framing nailer and 8d nails, inserting the nails at a 45-degree angle, through the edges of the blocks into the joists. This is called "toe-nailing" Use three nails for each side of each block. When you’re done – the blocks should resemble a straight board that intersects the joists.
Install two long boards, instead of the multiple short boards, if the joists run perpendicular to the wall you’re bracing. This is the alternate blocking method, and in this case, the open joist space will run to the other side of the basement and you need to install two boards, the same dimension as the existing joists, along the insides of the joist space. These are called trimmer joists.
Cut the trimmer joists so they extend from the far end of the basement to a point 6 inches short of the I-beam. Attach the trimmer joists, with 12d nails, to the insides of the existing joists, leaving a 6-inch gap next to where the I-beam goes.
Cut four boards to fit sideways in the 6-inch gap between the trimmer joists and the I-beam. Position the boards, one at a time, between the joists. The first one should be snug against cut ends of the trimmer joists, and the other three will fit side by side. This configuration will support the pressure from the I-beam.
Install the I-Beam
Set the I-beam on the center of the patio brick, in the hole, and position the top of the I-beam between the joists. The flat side of the beam should touch the bowed part of the basement wall.
Hold the beam in place and fill the hole with concrete, mixed as directed on the sack. Smooth the wet concrete level with the floor.
Let the concrete set for at least two days, and then install additional blocking between the top of the I-beam, if necessary, and the nearest joist or the blocks you already installed, depending on the joist configuration. You may have to drive the final block in with a hammer because it should fit tightly.
Mix sack concrete with just enough water until you can form a ball. Dry-pack the concrete in the gaps above and below the point on the wall where the beam meets the wall.
Things You Will Need
- Plumb bob
- Tape measure
- Concrete saw
- Electric jackhammer
- Patio brick
- Skill saw
- Dimensional lumber
- Framing nailer
- 8d nails
- 12d nails
- Dry concrete mix
- Wheelbarrow (for mixing sack concrete)
- Installing the I-beam will only stop the inward movement of the basement wall; you must patch existing cracks to prevent water leaking into the basement.
- Failure to add lateral blocking between the joists could result in movement of the floor joists. Since the bottom of the beam is secured with concrete, any future pressure exerted on the beam by the basement wall will create lateral pressure on the joist at the top of the beam.
- Don’t skip the dry-packing step. This step disperses the pressure between the beam and the wall, in the event the soil continues to push on the wall.