How to Repair or Replace Rotted Deck Posts

Deck posts are the skeleton of your deck. They carry the full weight of the structure down to the foundation, and when they rot, the whole system starts to fail. Rot happens silently—it spreads inside the wood where you can't see it, weakening the fibers until the post becomes punky and load-bearing strength drops. You might notice soft spots when you press a screwdriver into the wood, or see dark discoloration and a spongy feel. The bad news: you can't repair rotted wood. Once the cellular structure breaks down, the post is compromised. The good news: replacing a post is a straightforward weekend job if you have a jack, some temporary bracing, and don't mind getting under the deck. The key is temporary support—you're holding up a loaded structure, so safety is your only rule.

1. Find the Rot's Full Reach. Get under the deck and examine the post from all four sides. Use a screwdriver or awl to probe the wood at the base, middle, and top of the post. Push firmly—solid wood resists; rotted wood accepts the tool with little pressure. Mark the extent of soft spots with chalk or marker. If rot has spread into the rim joist or beam, the job gets bigger and you should consider a contractor. If it's isolated to the post, you can proceed.
2. Clear and Organize Your Space. Remove any stairs, railings, or hardware attached to the post. Sweep away debris around the base. Lay out all tools and materials nearby so you're not scrambling mid-job. Set up your jack, beams, and blocking in the work area. If you're replacing multiple posts, do one at a time.
3. Support the Load First. Set a hydraulic or screw jack on solid, level ground as close to the post as practical—usually 2 to 3 feet away. Position a 4x8 or 4x10 beam across the jack and under the existing beam or joist that the rotted post supports. Use cribbing (stacked blocks) to ensure full contact between beam and joist. Do not rely on the jack alone—the beam sits on the cribbing and the jack is the safety stop. Raise the jack slowly until you feel light resistance but not until the post is fully unloaded yet.
4. Shift Load to Support. Raise the jack slowly, one pump or turn at a time, until the rotted post is no longer carrying weight. You'll know it's unloaded when you can wiggle the post side to side with light hand pressure. Do not over-jack—you're not trying to lift the deck, just shift the load to the temporary support. Stop and check your level on the temporary beam again.
5. Extract the Dead Post. Using a reciprocating saw or handsaw, cut the rotted post at the top first, near where it meets the beam or joist. Cut it at the bottom, just above the post base or concrete pad. You'll be left with short segments that are easier to maneuver out from under the deck. Remove the top piece first, then the bottom. If the post is bolted or lag-screwed to the beam or rim, use an adjustable wrench or socket to remove the fasteners before cutting.
6. Check the Damage Zone. Once the post is out, look at the concrete pad, ledger board attachment, and beam where the post sat. If the base concrete is degraded or crumbling, chisel out loose material and plan to reset the new post on a fresh concrete pad or post base. Check the bottom of the beam or rim for rot—if present, address it now before installing the new post. If the post was bolted, verify the bolt holes are usable or mark where new holes need to be drilled.
7. Build a Solid Foundation. If the old concrete pad is solid, you can reuse it. If it's crumbly or missing, pour a fresh 6-inch concrete pad slightly larger than the post footprint—typically 12x12 inches. Let it cure per concrete manufacturer instructions (usually 24 hours) before installing the new post. For quick fixes, use a pre-made concrete post base that sits on existing concrete and accepts the new post without additional curing time.
8. Size the New Post. Measure the distance from the post base to the underside of the beam or joist the post supports. Subtract 1/4 inch to allow for settling. A new treated post should be cut square at both ends using a power miter saw or circular saw. Mark the top end clearly so you're installing it the right direction. Rough-sawn posts may have slight size variation—measure at the base, middle, and top, then cut accordingly.
9. Stand the New Post Plumb. Position the new post upright on the concrete base or post base. Use a level on two adjacent sides to ensure it's plumb. If the post doesn't sit flat on the base, shim it with cedar shims or stainless-steel shim stock until it's solid and level. The post should fit snugly but not be forced. Have a helper hold the post plumb while you work.
10. Lock Down the Base. If using a post base, bolt or screw it to the concrete pad per manufacturer instructions—typically lag bolts into concrete anchors or a bolted base plate. If setting the post directly on concrete, drill holes through the post into the concrete pad and install concrete anchor bolts (usually 1/2-inch diameter). Use a minimum of two bolts, one near each side of the post. Tighten bolts gradually and evenly until snug but not over-torqued.
11. Bolt the Beam Tight. At the top of the post, install a post-to-beam connector appropriate for your deck design. If the original post was bolted to the beam, drill new holes in the new post aligned with existing holes in the beam, and re-install lag bolts or through-bolts. If the post sat under a notched joist, cut a corresponding notch in the new post and seat it. Use multiple fasteners—never rely on a single bolt. Install at least two bolts per connection.
12. Transfer Load to Post. Once the new post is bolted top and bottom, lower the jack very slowly—one pump at a time. Watch for any movement in the surrounding structure. Lower until the temporary beam is no longer supporting weight but is still in contact. Wait 10 minutes, then lower completely. Remove the temporary beam and jack carefully, keeping the area clear. The new post should now be carrying its share of the load.
13. Seal and Test. Check all connections with a wrench to confirm bolts are tight. Look at the base and top for any gaps or movement. Walk the deck and listen for squeaks or soft spots—they indicate the post isn't fully connected or the deck has other structural issues. Once everything is confirmed solid, paint or stain the new post to match the rest of the deck. Leave any cut ends sealed with end-grain sealer or paint to slow future rot.