Deck Post Replacement: Shore, Swap and Reset the Footing

A rotted post is one of the most common reasons decks fail, and it often hides in plain sight at ground level where mulch, soil or splash water keeps the wood wet. Deck post replacement is a manageable project for an experienced DIYer on a low deck, but it involves temporarily carrying the weight of the structure, so the order of operations matters more than the carpentry itself.

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The short answer is: shore the beam first with temporary supports and jacks on both sides of the bad post, relieve the load slightly, remove the old post and its connectors, inspect or rebuild the footing, install a new post base anchor and a correctly sized pressure-treated post rated for ground contact, fasten it to the beam with approved connectors, then lower the load and remove the shoring. If the beam, ledger, footing or multiple posts are damaged, or the deck is high off the ground, this becomes a job for a licensed contractor and possibly an engineer and permit.

Below you will find signs that a post needs attention, the tools and materials involved, a step-by-step deck post repair process, troubleshooting, cost ranges and clear guidance on when to call a professional.

When Deck Post Replacement Is Needed

Before you plan a repair, confirm the problem is really the post. Inspect every post, especially at the base and where it meets the beam.

• Soft wood: Push a screwdriver or awl into the post near the bottom. If it sinks more than about 1/4 inch with light pressure, rot is likely.
• Cracks, splits or crushing: Deep checks are normal in treated wood, but crushing, heavy splitting or fungal growth are not.
• Leaning or sinking: A post that is out of plumb or a deck that has settled may point to a failing footing rather than the post.
• Corroded connectors: Rusted post bases, brackets or fasteners can weaken the connection even if the wood looks fine.
• Posts buried in soil: Older decks often have posts set directly in dirt or concrete, which traps moisture and accelerates rot.

If you find rot in the beam, joists or ledger board where the deck attaches to the house, stop and have the entire deck evaluated. A single post swap will not fix a structure that is compromised elsewhere.

Safety First: Structure, Permits and Digging

• Never remove a post without temporary shoring. Install temporary supports and jacks to carry the load before cutting or removing anything.
• Check permit requirements. Many jurisdictions require a permit for structural deck repairs, including posts and footings. Contact your local building department.
• Call 811 before digging. Always call 811 a few business days before digging a new footing so underground utilities can be marked.
• Protect yourself. Wear gloves, safety glasses and steel-toe boots. Use a dust mask when cutting treated lumber and wash hands before eating.
• Keep people off the deck. Nobody should stand on the deck while it is shored.

Tools and Materials

• Two adjustable steel shoring posts or bottle jacks rated well above the expected load
• Temporary 4×4 or 6×6 posts, plus solid blocking or pads to spread jack loads on the ground
• Level, tape measure and string line
• Reciprocating saw, circular saw and impact driver
• Pry bar, hammer and wrenches or sockets
• Shovel, post-hole digger and wheelbarrow
• Concrete mix, footing form tube if needed, and gravel for drainage
• New post base anchor (galvanized or stainless, sized for the post)
• Pressure-treated post rated for ground contact, typically matching or exceeding the original size
• Post-to-beam connectors and structural screws or bolts listed for the connector
• End-cut preservative for cut ends of treated lumber

Step-by-Step Deck Post Repair

1. Assess the Load Path

Identify what the post supports: typically a beam that carries joists above. Check whether the beam spans over the post continuously or splices at it. A splice at the post means the beam may need support on both sides of the joint.

2. Install Temporary Shoring

Set solid pads on firm ground about 12 to 24 inches from the bad post on each side, under the beam. Place a jack and temporary post on each pad, plumb them, and snug them to the underside of the beam. Raise the jacks slowly and evenly only enough to take the load off the post, usually 1/8 inch or less. Raising too much can crack decking, pop fasteners or damage the ledger.

3. Remove the Old Post

With the beam supported, remove the fasteners connecting the post to the beam and to its base. If the post is set in concrete or soil, cut it off near grade. Then pull or dig out the remaining stub. Keep an eye on the shoring the entire time; if anything shifts, stop and re-level.

4. Inspect or Rebuild the Footing

Examine the footing. A cracked, undersized or sinking footing should be replaced. Dig to below the frost line required in your area and to undisturbed soil, add a few inches of compacted gravel, and pour a concrete footing sized per local requirements. Your building department can tell you the minimum footing size and depth. If you can, set the new footing so the post sits above grade on a post base rather than being buried.

5. Install the Post Base Anchor

A post base anchor lifts the bottom of the post off the concrete so it can dry out, which dramatically extends its life. Set a wet-set anchor into fresh concrete, or use a mechanical anchor into cured concrete with the specified anchor bolt. Make sure the base is centered under the beam and level.

6. Cut and Fit the New Post

Measure from the top of the post base to the underside of the beam with the load supported at the correct height. Cut the post square, treat the cut end with preservative, and set it into the base. It should fit snugly without forcing the beam up.

7. Fasten the Post

Attach the post to the base and to the beam using connectors and fasteners approved for the specific hardware. Follow the connector manufacturer’s installation instructions for fastener type and quantity. Avoid relying on toenailed screws or nails alone.

8. Lower the Load and Remove Shoring

Lower the jacks slowly and evenly so the beam settles onto the new post. Check that the post is plumb and the beam is level, then remove the shoring. Walk the deck and look for gaps, cracks or movement.

Troubleshooting

• Beam sags after removing the post: Shoring was not tight or evenly placed. Re-shore and adjust before installing the new post.
• New post too short: Do not add shims made of soft wood. Recut a new post or use an adjustable post base designed for the purpose.
• Footing sinks: The soil was disturbed or the footing too small. Dig to undisturbed soil and enlarge the footing.
• Decking cracks or pops: The beam was jacked too high. Lower gently and reset fasteners.
• Rot found in beam or joists: Stop and call a contractor to evaluate the structure.

Cost of Deck Post Replacement

A DIY single-post replacement typically costs roughly $60 to $250 for lumber, concrete, a post base anchor, connectors and jack rental, depending on post size and whether you rebuild the footing. Professional deck post replacement often ranges from a few hundred dollars per post for a simple swap to more when footings, beams or permits are involved. Replacing several posts or correcting structural issues can cost significantly more, so get written quotes that detail the scope.

When to Call a Licensed Professional

Hire a licensed deck contractor, and in some cases a structural engineer, when the deck is more than a few feet off the ground, when multiple posts or the beam show rot, when the ledger board attaching to the house is loose or decayed, when footings need to be redesigned, or when your jurisdiction requires a permit for structural work. A pro can shore the structure safely, size footings correctly and confirm the connections meet local requirements. Deck post replacement done correctly restores stability and safety; done poorly, it can create hidden weaknesses that fail when the deck is loaded with people.