Step-by-step fix
Step 1: Confirm the deck post is really the problem
- Inspect the full height of the pressure treated deck post, especially the bottom few inches where rot, splitting, insect damage, or crushing usually shows up first.
- Probe any dark, soft, or cracked areas with a screwdriver. If the wood is soft enough to sink in easily, the post is no longer sound.
- Check the beam above and the footing or post base below. Make sure the damage is not mainly in the beam, ledger, connector, or concrete footing.
- Measure the existing post size and note how it is attached at the top and bottom so you can match the replacement.
If it works: You have confirmed the post itself is damaged and the replacement size and connection style are clear.
If it doesn’t: If the post is solid but the base hardware, beam, or footing is failing, repair that part instead of replacing the post alone.
Stop if:- The beam above the post is badly rotted, split, or sagging.
- The footing is cracked, leaning, sunken, or too loose to support a new post.
- The deck feels unstable enough that you cannot safely support it before removal.
Step 2: Support the deck before removing the post
- Clear the area under and around the post so you have room to work and a solid place for the jack and temporary support.
- Place the jack on a stable base and position a temporary support post close to the damaged post, under the beam.
- Lift only enough to take the weight off the old post. Usually this is a small movement, not a major lift.
- Watch the beam and deck surface as you lift. Stop once the load is supported and the old post is no longer carrying weight.
If it works: The deck load is safely supported by the temporary setup, and the damaged post is unloaded.
If it doesn’t: If the jack sinks, shifts, or will not hold steady, reset the support on firmer blocking before continuing.
Stop if:- The deck shifts suddenly or the beam starts twisting as you lift.
- You cannot create a stable temporary support setup.
- The area below the jack is soft, sloped, or otherwise unsafe.
Step 3: Remove the old pressure treated deck post
- Remove bolts, screws, brackets, or post base hardware connecting the post to the beam and footing.
- If the post is trapped by tight framing, trim it into sections so it can come out without forcing the deck structure.
- Clean the connection points after removal so the new post can sit flat and attach cleanly.
- Recheck the opening height from footing to beam with the deck still supported, and compare it to the old post length.
If it works: The old post is out, and the top and bottom connection points are ready for the new post.
If it doesn’t: If fasteners are rusted in place, cut them flush and remove the remaining pieces before fitting the new post.
Stop if:- You uncover hidden rot in the beam, rim area, or nearby framing.
- The post base or connector is too damaged to reuse safely.
- The measured opening changes noticeably because the temporary support is moving.
Step 4: Cut and fit the new post
- Cut the new pressure treated deck post to match the measured height, using the old post only as a rough reference if it was damaged or compressed.
- Dry-fit the post in place and check that it sits flat at the bottom and meets the beam cleanly at the top.
- Use a level on two sides to set the post plumb.
- Make small trimming adjustments if needed so the post fits snugly without being forced into place.
If it works: The new post fits properly, sits flat, and is plumb before final fastening.
If it doesn’t: If the post is too short, do not shim it with random scraps. Cut a new post to the correct length or correct the base connection with the proper hardware.
Stop if:- The new post cannot sit flat because the footing or base is uneven or damaged.
- The beam contact area is too deteriorated to support the new post properly.
Step 5: Fasten the new post and transfer the load back onto it
- Attach the post at the top and bottom using the same style of structural connection the deck was designed to use, replacing badly corroded hardware as needed.
- Tighten all fasteners so the post is secure but do not pull the post out of plumb while fastening.
- Slowly lower the jack so the beam settles onto the new post.
- Watch for gaps opening at the top or bottom as the load transfers, and make final plumb and fastener checks.
If it works: The new post is fully fastened, carrying the load, and remains plumb with tight connections.
If it doesn’t: If a gap appears when the load transfers, raise the support slightly, correct the fit, and refasten before lowering again.
Stop if:- The post starts to crush, split, or kick out of plumb under load.
- The beam does not bear evenly on the top of the post.
- Fasteners will not tighten because the surrounding wood is too damaged.
Step 6: Test the repair in real use
- Walk the deck area above the repaired post and feel for bounce, movement, or new noises.
- Look at the post, beam connection, and base while someone else shifts weight on the deck.
- Check again after a day or two, especially after rain, to make sure the post stays plumb and the base area stays firm.
- If the old post failed from trapped moisture, improve drainage or splash exposure around the base so the new post lasts longer.
If it works: The deck feels solid in normal use, and the new post remains tight, plumb, and fully supported.
If it doesn’t: If the deck still moves or the post connection opens up, the problem may include the beam, footing, or nearby framing and needs a broader repair.
Stop if:- The deck still sags, shifts, or bounces noticeably after the post replacement.
- You see new cracking, separation, or movement in nearby structural parts.
Replacement Parts
Repair Riot may earn a commission from qualifying purchases, at no extra cost to you.
FAQ
Can I replace a deck post without jacking up the deck?
Usually no. A load-bearing deck post needs the weight taken off it before removal. Even a small amount of controlled lifting is safer than trying to force the post out under load.
How do I know if the post or the footing is the real problem?
If the wood is soft, split, crushed, or rotted, the post is likely the problem. If the concrete is cracked, leaning, sunken, or loose, the footing may be failing instead. Check both before buying parts.
Can I splice in just the bottom of a rotted pressure treated deck post?
For a load-bearing deck post, a full replacement is usually the cleaner and more reliable repair. A partial patch often leaves you with weak connections and hidden damage still in place.
What size replacement post should I buy?
Match the existing post size and length, and confirm the top and bottom connection points before ordering. Measure the actual installed opening after the deck is supported, because the old post may have shrunk, rotted, or compressed.
Do I need to replace the post base hardware too?
Replace it if it is bent, heavily rusted, loose, or no longer holds the post securely. A sound new post still needs a solid connection at the base and beam to do its job.