How to Add Support Beams to a Basement Wall


Basement walls are constantly acted upon by pressure from the wall’s exterior due to the dirt piled against the walls outside the structure. While most walls hold against the pressure, those that begin to give in can bow inward, developing cracks that can lead to moisture running through the walls, or weaken the structure of the wall, threatening collapse. Adding support beams to the walls can brace them against the pressure, strengthening the wall to avoid further inward movement.

Things You'll Need

  • Chalk
  • Jackhammer
  • Tape measure
  • 4-inch angle grinder
  • 2-by-10-inch boards, 48 inches long
  • 3/8-inch lag bolts
  • Drill
  • Carpenter’s level
  • Rubber gloves
  • Concrete mix
  • Large bucket
  • Steel trowel
  • Mark the locations for the positioning of the I-beams on the floor along the wall with a piece of chalk. Space the beams 4 feet apart for concrete basement walls and 3 feet apart for block or stone walls.

  • Break a hole through the concrete slab at the base of the wall 1 foot in diameter at each of the marked beam locations with a jackhammer. The hole should extend about 6 inches beneath the base of the poured wall. Clear away the concrete debris.

  • Measure the height of the ceiling from the base of the hole with a tape measure. Cut the steel beams to fit the measured height with a 4-inch angle grinder.

  • Place the beam into the hole with the flat side of the beam flush against the wall and raise the beam to the ceiling.

  • Brace the top of the beam in place with a 2–by-10-inch piece of lumber perpendicular to beam and long enough to be screwed into the wooden joists on either side of the beam, when the wall you are repairing is perpendicular to the ceiling joists. Pre-drill a pilot hole through the 2-by-10-inch blocking lumber and into the ceiling joist and secure the block to the joists with 3/8-inch lag bolts and a drill containing a bolt head. Have someone assist with the bracing process by holding the beam in place as you snug the blocking lumber up against it and secure the 10-inch-wide faces of the blocking lumber to the joists. If the joists run parallel to the wall you're repairing, brace the beam with a block that runs from the outer edge of the beam across the first three joists, a minimum of 48 inches. Secure the blocking lumber into the bottom edges of the joists with the lag bolts.

  • Set a carpenter’s level vertically against the base of the beam on the front and side to adjust the beam within the hole until it’s plumb and square against the wall. Brace the beam in place with short lengths of 2-by-4-inch boards extending from the front of the beam at the bottom of the hole to the concrete slab and from the rear to the wall so that the beam is plumb and square.

  • Put on a pair of rubber gloves. Mix a stiff batch of concrete that has just enough water to hold together when formed into a ball in a large bucket. Pack the space between the beam and the wall with the stiffened concrete. Fill the hole in the floor with the concrete as well. Smooth out the concrete along the edges of the beam and the surface of the floor with a steel trowel. Allow the concrete 10 days curing time before touching the beams.

Tips & Warnings

  • Have a structural engineer determine the beam location for you to provide the most efficient spacing of the beams against the wall.

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  • Photo Credit Hemera Technologies/ Images
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