How to Repair a Damaged Carrying Beam
Reinforce and repair a structural carrying beam using temporary shoring posts, structural LVL sisters, heavy-duty through-bolts, and adhesive for permanent load support.
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🧰 Required Tools & Equipment
- ✓ Hydraulic bottle jack or screw jacks (rated 10+ tons)
- ✓ Circular saw or reciprocating saw
- ✓ Heavy-duty 1/2-inch drill with 1/2-inch auger bit
- ✓ Impact wrench or socket set
- ✓ Heavy C-clamps or bar clamps (4+)
- ✓ 4-foot level
- ✓ Tape measure
📦 Materials & Supplies
- ✓ LVL (Laminated Veneer Lumber) or matching dimensional timber
- ✓ 1/2-inch Grade 5 through-bolts with nuts and heavy washers
- ✓ Heavy-duty structural construction adhesive
- ✓ 4x4 or 6x6 temporary shoring posts
- ✓ 2x6 or 2x8 dimensional lumber for top/bottom shoring plates
⚠️ Safety Checkpoints & Warnings
- • Ensure bottle jacks and shoring posts rest directly on a solid concrete foundation or reinforced floor plates, never on unsupported subfloor.
- • Only lift structural jacks 1/8 inch at a time to take load off the beam without cracking upstairs drywall or binding doors.
- • Wear safety glasses, hearing protection, and structural gloves throughout lifting, cutting, and drilling operations.
📋 Step-by-Step Guide (7 Steps)
Erect Temporary Shoring Walls
Place a continuous 2x6 sole plate directly on the concrete slab or reinforced joists parallel to the damaged beam, roughly 18 to 24 inches away. Cut 4x4 or 6x6 posts to fit vertically beneath a matching top plate tight against the floor joists. Plumb each post with a 4-foot level and toenail them securely into the top and bottom plates.
- • Vertical shoring posts stand perfectly plumb under a continuous horizontal top plate.
- • Top plate sits flush against all supported floor joists with zero visible gap.
- • Placing shoring posts directly on a thin, unsupported section of wood subfloor instead of transferring load to solid concrete.
Preload Jacks and Relieve Beam Stress
Position heavy-duty screw jacks or hydraulic bottle jacks directly under the shoring beam. Pump or turn the jacks slowly just until the floor load transfers to the temporary wall. Raise the assembly no more than 1/8 to 1/4 inch, checking joists for settling relief.
- • Temporary posts are under firm compression with no lateral movement when pushed.
- • A hairline relief gap appears between the top of the damaged beam and the joist bottoms.
- • Jacking too fast or too high, which can crack plaster, drywall, or pop tile upstairs.
Cut Away Damaged and Rotted Timber
Inspect the carrying beam to identify the boundaries of rot, insect damage, or structural cracking. Use a reciprocating saw to cut away punky or decayed sections back to sound, solid wood. Scrape away debris and wire-brush the remaining solid surface clean.
- • All soft, darkened rot is removed, leaving only solid, dry timber core.
- • Clean, squared cut lines where rotted wood was excised.
- • Leaving rotted or fungal wood encapsulated inside the new sistered repair.
Cut and Fit Reinforcement Sister Plies
Measure the full span required for the sister beam, extending at least 2 to 3 feet beyond the damaged zone on both sides (or bearing-to-bearing if fully compromised). Cut matching depth LVLs or dimensional lumber. Test-fit the new piece against the beam face to confirm flush top and bottom alignment.
- • Sister piece spans well past the damaged area and rests flush against the original beam face.
- • Top edge of the sister piece aligns horizontally with the joist underside.
- • Cutting sister material shorter than structural overlap requirements (minimum 2-3 feet past damaged zone).
Adhesive Application and Clamping
Apply a heavy, continuous zigzag bead of structural construction adhesive along the mating face of the existing beam. Hoist the sister beam into place and seat it flush against the original member. Clamp the sandwich tightly using heavy-duty C-clamps spaced every 16 to 24 inches until adhesive squeezes out.
- • Sister beam is clamped dead flush with no visible light between the mating faces.
- • Uniform squeeze-out of construction adhesive along the entire seam line.
- • Failing to clamp prior to drilling, allowing the drill bit to push the two beams apart and trap wood shavings between them.
Drill and Install Structural Through-Bolts
Drill 1/2-inch through-holes staggered in pairs (top and bottom of beam, 2 inches from edges) every 12 to 16 inches along the sistered length. Push 1/2-inch Grade 5 bolts through with thick structural washers on both sides. Tighten nuts securely using an impact wrench or heavy socket until washers seat slightly into the wood grain.
- • Staggered zig-zag pattern of hex bolt heads with wide structural washers across the beam face.
- • Washers compressed tightly flat against wood surface with 2 to 3 threads exposed beyond every nut.
- • Drilling holes in a straight horizontal line along the center axis, which can promote grain splitting.
Lower Jacks and Verify Load Transfer
Allow construction adhesive to cure according to manufacturer instructions. Gradually open jack valves or back off screw jacks to gently transfer the home's structural weight back onto the repaired beam. Check the repaired beam with a 4-foot level and inspect all joist bearing surfaces for complete contact before dismantling the shoring wall.
- • Floor joists rest flat and flush across the entire top surface of the reinforced beam.
- • 4-foot level indicates the beam is straight with no sagging under full load.
- • Dropping the jacks suddenly instead of relieving pressure in slow, controlled increments.
Credit: inspired by an original tutorial by This Old House — watch the original on YouTube.
Don’t have everything?
- No Impact wrench? 1/2-inch drive ratchet with deep-well socket and a combination wrench on the bolt head
- No LVL (Laminated Veneer Lumber)? Kiln-dried #1 structural grade 2x dimensional lumber doubled to match beam depth