How to Replace Rotted Deck Posts

Nothing lasts forever, but when properly maintained, an elevated deck will endure for many years. Because a wood structure can rot slowly and almost invisibly, preemptive maintenance is essential to extending your deck’s life — and ensuring its safety.

One of the most common and dangerous structural problems with older decks is rotting support posts. This is often caused by improper installation or a poor choice of material. If your deck is older, look for warning signs such as large cracks in the wood or posts that are buried below grade. Be sure to fix the problem before it’s too late: A deck with a failing structure is a disaster waiting to happen.

Given enough time and unfavorable conditions, even pressure-treated deck posts can rot (see photo above). Without intervention, this post would have caused the deck to collapse.

Replacing deck posts is a project that many DIYers can tackle, but it requires that you work methodically, safely and in the proper sequence. The photos below offer an overview to help you understand the process.

Step by step
Before you start, be sure the deck structure is sound and free of rot. Check common problem areas such as the ledger board, joists and stairs. Also make sure the deck is level.

If the posts have no concrete footings (as is sometimes the case with buried pressure-treated posts), you’ll need to pour them. The top of the footings should be above grade and not covered with dirt or gravel (photo 1), and they must extend below the frost line. Check with your local code authority to determine what’s required.

The bottom of this deck post was buried under gravel. Although it looked good, the gravel prevented proper drainage and eventually caused the base to rot.

If safe footings are present, mark the position of the existing posts for the metal mounting bracket you’ll install later. Make sure the existing posts are plumb so you can position the new posts correctly (photo 2).

Before removing the old post, check that it’s plumb; then mark its footprint so you can position the new post correctly.

In most cases, the best material for replacement posts is pressure-treated wood (it must be rated for ground contact), but cedar or other rot-resistant lumber will work. Use stock that’s at least as large as — or larger than — the existing post.

Replace only one post at a time. You’ll need to use a jack to support the deck as you remove and replace each post (photo 3). A tool-rental store can advise you on the correct size for your job.

Use a metal pole jack to support the deck as you replace each post. Use blocks on the top and bottom of the jack to spread the load for stability and to prevent damage.

Place the metal jack in position and adjust it so that it just relieves the load off of the post. Use blocking on the top and bottom of the jack to distribute pressure. Be sure to plumb the jack to prevent it from kicking out when it’s under load.

The way posts are attached to the header will vary, but you’ll probably need to remove metal straps and/or cut away nails or screws (photo 4). You may want to get some help bracing the post to prevent it from falling.

The top of the post will probably be fastened to the header with screws or nails. Use a reciprocating saw and a thin metal-cutting blade to sever the fasteners.

Once you’ve removed the old post, mark the position of the bracket bolt on the footing (photo 5). Bore the hole with a hammer drill to the recommended depth for the bolt (photo 6). Use concrete fasteners, such as Red Head concrete sleeve anchors, or Simpson Strong-Tie Epoxy to secure the threaded rod into the hole. When using a sleeve anchor, thread the nut before driving the fastener home (photo 7). That way if the threads are damaged, you won’t need to chase the threads to screw on the nut.

Center the metal post bracket over the marked footprint; then mark the center for drilling the bolt hole. Note that the bracket elevates the post off of the ground.

Bore the bolt hole with a hammer drill and a bit that’s slightly larger than the bolt’s diameter. Drill no deeper than is necessary for the bolt to extend to the correct height.

Clear excess dust out of the bolt hole; then push the bolt into the hole so it’s snug. Thread the nut onto the bolt and then hammer the bolt into the hole so it expands.

Adjust the jack so the deck is level; then mark the length of the post. Mark top and bottom; then use a miter saw to trim the excess material. Before installing the new post, apply sealer to both ends to prevent checking and splitting (photo 8).

Before installing the new post, brush sealer on both ends to prevent moisture infiltration into the wood and ward off rot.

Position the post; then lower and remove the jack (photo 9). Nail the bottom of the post to the bracket; then check for plumb on two sides and toescrew it into the header (photo 10). Make minor adjustment with a block and hammer. Replace trim pieces if necessary. Install metal straps or brackets between the post and header to prevent detachment caused by wind uplift. (Be sure to adhere to the building codes for your area.)

Center the post in its bracket and under the header with the jack still supporting most of the load. Check for plumb; then release the jack.

Drive a few nails through the bracket; then check for plumb again before installing the remaining fasteners on the top and bottom of the post.

If you used pressure-treated wood, wait two months before you prime and paint the new posts. With most other wood, you can apply paint or stain immediately.