How to Replace a 6×6 Wood Deck Post

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I’ve stabilized the deck addition and will now build a full height temporary support post and jack up the deck to replace the 6×6 deck post. This project is continued from How to Pull Together a Sagging Wood Deck. Also see the project introduction in How to Repair a Sagging Wood Deck if you’ve just landed here.

How to Replace a 6×6 Wood Deck Post

Build a Temporary Support Post

Two posts are made using 2×6’s and 2×4’s to jack up the wood deck:

  • Jack post – is a foot or so shorter to allow room for the hydraulic bottle jack to sit on the post.
  • Temporary Support Post – to support the deck after the jacking and removing the old deck post.

I carefully measured the 14ft 8in height from the basement patio concrete slab to the bottom of the 2×10 deck beams, then built a full height temporary support post with 12 feet long 2×6 and 2×4 kiln dried lumber while leaving room for the base and end caps. 16 feet long boards would have avoided splicing boards but it was easier to haul 12 foot boards in the minivan. The base of the support post (facing the camera) has yet to be made. The temporary support and jack posts are shown together here:

Jack Up a Wood Deck - Temporary Support and Jack Posts

Jack Up a Wood Deck – Temporary Support and Jack Posts

The temporary support post will be holding up the deck for several weekends until I get the new concrete footer poured and 6×6 wood post installed. I therefore made it stronger using Simpson Strong-Tie SD #9 x 2-1/2 structural screws. I drove wood shims between the splice joints to ensure a continuous load bearing path. (Take care to stagger the splice joints.) This probably wasn’t necessary since the SD #9 screws will transfer the shear loads but it’s a simple safety precaution:

Wood Deck Repair - Temporary Support Post Construction

Wood Deck Repair – Temporary Support Post Construction

The Simpson Strong-Tie SD hex head screws were a pleasure to use. I used a Malco MSH14P Magnetic Hex Driver bit which held the screws well.


After pulling out the 16 penny nails that fastened the joists to the deck post and removing the 4×4 knee bracing, I installed Simpson Strong-Tie ML26Z angle with only two SDS 1/4 by 2-1/2 inch structural screws to reinforce joist connection.

The reason for only two screws now is to allow for some movement when jacking up the deck:

Deck Repair - Simpson Strong Tie ML26Z Angle Joist Reinforcement

Deck Repair – Simpson Strong Tie ML26Z Angle Joist Reinforcement

Referring to the above photo, I thought it odd that the home builder notched the inner 2×10 joist for the 2×2 ledger board over the deck post. This was completely unnecessary.

How to Jack Up a Deck

Caution: These next steps are potentially dangerous and if performed incorrectly or if the deck is not structurally sound, could result in a deck collapse causing property damage, injury and/or death. Please hire a professional deck builder if your are unsure of your abilities and deck structure.

I was working by myself today and needed a way to hold the jack post in place, so I fastened two 2×4 braces with SD #9 screws to the sides of the deck post. The 2×4 braces were snug and pinched the jack post to hold it while I climbed the ladder to set up the hydraulic bottle jack:

Wood Deck Repair - Jack Post Setup

Wood Deck Repair – Jack Post Setup

Another view of the jack post and 2×4 fork braces:

Wood Deck Repair - Jack Post Top End Detail

Wood Deck Repair – Jack Post Top End Detail

I’m using the same concrete block and 2×12 base as when I sistered the other deck post to fix the improper beam splice:

Wood Deck Repair - Jack Post Support Block Detail

Wood Deck Repair – Jack Post Support Block Detail

After tying a safety rope around the jack post, I set the Torin 6 ton hydraulic bottle jack and 4×4 block on the jack post, adjusted the screw and slowly jacked up the deck:

Jacking Up a Wood Deck

Jacking Up a Wood Deck

The deck is 14 feet 8 inches high from the patio slab to the top of the deck post:

Jacking Up Wood Deck - Hydraulic Bottle Jack on Jack Post

Jacking Up Wood Deck – Hydraulic Bottle Jack on Jack Post

I raised the deck very slowly about 1/2 inch at a time while listening for any cracking, checking for lateral (side) movement or pulling away at the ledger board. The deck creaked and groaned a slightly but was otherwise good. Pumping the 6 ton bottle jack was very easy and had it no problem lifting the deck.

I also considered the wisdom of jacking while underneath the deck on the 24 foot extension ladder. For me, the most convenient place with good footing on the concrete patio slab because the ground drops off about 3 feet at the corner post. Still it’s best to place the ladder outside the deck if possible to minimize risk. Hopefully your deck isn’t so high as mine.

Jack Up and Level the Wood Deck

I had previously determined the deck had sagged 2-1/2 inches. I placed scrap 2×6 (1.5 inch thick actual) and 5/4 x 6 wood (1 inch thick) on the post as I jacked the deck up a total of 2-1/2 inches to level:

Jacking Up Wood Deck to Level

Jacking Up Wood Deck to Level

Walking gently on the deck, I placed the 5 foot spirit level on the deck corner to check if it was level after jacking. After raising it 2-1/2 inches it was still a bit low:

Sagging Wood Deck Repair - Level after Jacking Up

Sagging Wood Deck Repair – Level after Jacking Up

I swapped out the 1 inch thick 5/4 block for a 1-1/2 inch thick 2×6 block for a total of 3 inches of blocks. Rechecked the spirit level and the deck is now level after raising it 3 inches.

The deck must be jacked up not only until it is level, but a bit higher so I can set the new 6×6 deck post in place. I raised it a some more and placed a 3/4 inch thick block on top of the stack:

Jack Up Wood Deck to Replace Deck Post

Jack Up Wood Deck to Replace Deck Post

The deck corner is now slightly higher than level after jacking:

Sagging Wood Deck Repair - After Jacking

Sagging Wood Deck Repair – After Jacking

Next I’ll setup the full height temporary support post and remove the jack post in How to Replace a 6×6 Wood Deck Post – Part 2.

Take care,

Bob Jackson

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7 Comments

  1. Chuck June 25, 2016 at 1:47 pm - Reply

    Thanks Bob for you great explanations and detailed pictures and drawings. They are very helpful. I have to replace a 22′ 6″ x 12″ beam that holds up a 45′ long deck. I built the deck 25 years ago with a contractors help but wasn’t sure how to best create temporary support beams. Your outstanding examples have given me many ideas how to go about it that I had not considered. I find so many how to”s in many areas of repairs or construction so poorly done and find yours to be outstanding. THANK YOU!!!!

  2. Cole November 17, 2016 at 5:40 pm - Reply

    Bob, Thanks for the ideas. In the final pic captioned, “Sagging Wood Deck Repair – After Jacking”, it appears the problem guardrail post has been removed. Is that just incidental or also necessary to allow flex in the rail? Thanks!

    • Bob Jackson November 17, 2016 at 6:23 pm - Reply

      The guard post was removed in How to Pull Together a Sagging Wood Deck because it was at the intersection of the sagging deck extension and in the way. But yes, the guard rail needs to be separated to allow for movement during the repair. Otherwise the guard rail would buckle.

  3. Michael Lance May 10, 2018 at 11:39 am - Reply

    My deck looks very similar to yours in that the joists attach to the ledger on one end and the rim joists are sitting directly on the support posts. Where mine differs is that some of the guard posts are just a continuation of the support post. That is, the support post was notched to allow the rim joist to sit on it, but the support post continues upwards to form a guard post. My problem is that I have some guard posts that are rotting from the inside out at the top, and I wish to replace them. Since some of them are part of a support post, just replacing them is not a great or easy option. I am currently considering two options, both of which will result in the guard and support posts NOT being together: Option 1 is to move the guard posts to the outside of the rim joist – that would involve relocating all of the guard rails, but then guard post replacement would be easy and anchoring them would be simper. Option 2 is to move the support posts inward away from the rim – I would run a double 2 X 10 or 2 x 8 to span the joists (so joists would rest on that) and support that span with new/relocated support posts. Again, the result would be support and guard posts no longer co-located.

    FWIW, I have had a contractor estimate the repair, and basically they proposed filler for the rotten guard posts and shims in the notches and toe-nailed ends to eliminate wiggle. That does not address what I see as a problem of maintenance going forward – any time work on a guard post is needed, there are good odds a support post will be involved. Also, the estimate for what they said they would do seemed way high.

    Can you offer any insight/advice? I would love to do the work myself, but my time is limited. Option 2 is the one I would prefer, but relocating support posts, especially by myself, seems like a pretty big job….

    • Bob Jackson May 11, 2018 at 3:05 pm - Reply

      As a general rule, all repair / rebuild work should conform the current wood deck building code as closely as possible.

      If the deck is more than 15 years old then Option 2: Replacing the support posts and rebuild the deck railing is best, although it’s the most expensive and labor intensive. Replacing a deck post is a big job and dangerous if you’re not careful. I mostly worked by myself and sweated a lot. But most deck posts aren’t 14 ft 8 in tall like mine so your job shouldn’t be as challenging.

      Option 1: Keep the support posts and rebuild the deck rail on the outside of the rim joists is reasonable if the support posts are in good condition. This is what I did in How to Build Code Compliant Deck Railing.

      The Planning and Building Wood Deck Stairs with Landing may be helpful as it’s a complete teardown and rebuild – new concrete footers, 6×6 posts, landing (a landing is “free standing deck” per the Code) and railing.

      I wouldn’t do wood filler & shims because that is not a structurally sound repair.

      • Michael Lance May 14, 2018 at 10:40 am - Reply

        Mr. Jackson:

        Thanks for the reply. The deck is only 10 years old, and my suspicion is the 6 x 6 stock used for the guard posts was either not treated well (treatment did not fully penetrate to center), or if that is common for a 6 x 6, the center was exposed and should have been capped. I can blame that (not capping) on me, however I have cleaned and treated the deck a few times – I guess the exposed center grain is just no match for the elements.

        My support posts are in the 12′ to 15′ range, and so would be a bear to manage alone. Aside from the difficulty handling the components and setting it all up myself, my main concern is getting the post anchored correctly in a new spot and getting the height right. I would be willing to pay to have it done, and then I would do the guard posts myself (comparatively easy), but getting an estimate is hit-or-miss, and then getting a contractor to call back after doing an evaluation is almost impossible. The first contractor to actually show up and do the estimate and then call me back with a proposal would likely get the job!

        Thanks again for the input.

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