How to Replace a Rotted Deck Post

DECK POSTS are the primary structural support for your outdoor living space, yet they are the most vulnerable to the elements. Constant moisture from the ground, combined with debris buildup at the base, eventually leads to the soft, spongy rot that compromises the integrity of your entire deck. Ignoring a failing post isn't just an eyesore; it is a structural liability that puts everyone on your deck at risk. Replacing a post requires careful weight distribution and precise leveling. You are essentially taking the load off the damaged member and shifting it to temporary shoring while you reset the foundation. Done well, the new post will be pressure-treated for ground contact, properly flashed, and secured to prevent future moisture intrusion. This repair brings the deck back to code and restores the solid foundation it needs.

  1. Stabilize Before You Start. Place a heavy-duty screw jack or 4x4 support post on a solid base near the damaged post. Slowly raise the jack just enough to take the weight off the old post without lifting the beam off the joists.
  2. Cut Out the Rot. Remove any fasteners connecting the post to the beam and the base anchor. Use a reciprocating saw to cut through any rusted bolts if necessary, then carefully pull the damaged post out.
  3. Test the Foundation. Check the concrete pier for cracks or uneven leveling. If the concrete is failing, you must clear the area and pour a new pier before continuing.
  4. Lock in the Standoff. Attach a new galvanized post-to-concrete anchor to the pier using concrete anchor bolts. Ensure the anchor keeps the wood at least one inch above the concrete surface to prevent moisture wicking.
  5. Set the New Post. Measure the distance from the new base anchor to the deck beam and cut a pressure-treated 4x4 or 6x6 to length. Set the post into the anchor and ensure it is plumb on all sides.
  6. Seal Against the Elements. Bolt the post to the beam using structural hardware, such as a post-to-beam bracket. Once secure, remove the temporary jacks and apply a high-quality water-repellent deck sealer to the cut ends.