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I have a raised deck (no idea how old; maybe 10-15 years). It is supported by 4x4 posts. I couldn't find any concrete footings by digging (maybe I didn't go deep enough). Much of the posts are exposed to the soil with no signs of rot yet. I had a deck inspection and it was recommended to replace the 4x4 with 6x6 and install concrete footings (I assume new code since deck was installed). Per code they need to be below the frostline 30in (in maryland) and 20x20 dimensions. Most of this seems fairly straightforward: removing everything from deck, support deck on 6x6 wedged on wood, dig out old posts, pour concrete into footing form and sonotube, install bracket before dries, let dry 3-7 days, install new 6x6 on mount and new brackets, lower deck. Should take about 90 bags of concrete across 9 posts. I plan on installing a waterproofing system, so there shouldn't be any rain water under the deck any longer.

The annoying posts are the ones closer to the house which is what is making me rethink this recommendation. The posts are:

  • Under the L-shaped area of my deck in a cantilevered configuration.
  • Within 5' of the foundation which means I need to go down to the house foundation per code. I'm hoping that too is 30in at the frost line.
  • I have a drain pipe next to one of the posts. Looks like it's made of pvc, ok maybe i can move it if needed
  • I have a drain gutter also next to it, ok maybe I can deal with that.
  • Most annoying: I have one post (actually 2 2x4) right next to the foundation. Now this I don't know how to deal with. What would a footing even look like that that butts right up against the house?

So my options are:

  1. just do the work, and install a 'partial footing' that hugs the foundation of the house (probably without using any sort of pre fabbed form)
  2. only install footings on the posts away from the house (since the one's under the deck soon wont have any rain in that area)
  3. do the work on all posts except the one next to the foundation, and waterproof that one as much as possible.
  4. don't bother with this recommendation since I'll get another 10-15 years out of these posts?

Question: How much additional life would I get out of these posts, in particular the one that butts against my foundation?

Post butting into foundation Other 'problem' post One of the posts away from the foundation L-shaped portion of deck

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    That was a whole lot of reading to get to a fairly simple question. :P Answer: no one knows. Specific soil conditions, climate, etc. factor in, but the most important question might be remaining concentration of anti-microbial material in the wood. That leaches out over time. We aren't chemists and we don't have wood samples, nor do we have any sort of actuarial tables from which to draw conclusions based on chemical analysis. You'll have to make the call based on average treated lumber lifetime, budget, and will.
    – isherwood
    Oct 1 at 15:31
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    Haha. Yeah it's my secret way to get people to comment on other parts of the process without asking 5 independent questions since SO never seems to like multiple questions or 'general comments' type questions. ;). It seems to work about 50% of the time ;) Thanks for your response. I'll see if I can get any more information about my area and maybe the lumber used.
    – Joe
    Oct 1 at 15:40
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    I may be long-winded, but at least I'm manipulative!
    – isherwood
    Oct 1 at 15:47
  • HAHAHA! So True!
    – Joe
    Oct 1 at 15:49
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This is a little long to be a comment, so I will leave it as an answer even though I agree with isherwood's take on the question.

To add to what he said in a comment - the photos posted don't show significant deterioration (yet). The construction isn't up to my standards or my understanding of code, but has been there already for however long and seems to be standing up to the elements okay so far.

Concrete footers below the frost line, supporting brackets with sufficient posts is standard now. Many decks were created before that barely meet minimums or use alternate construction for some other reason. Decks have a limited life and rather than replace parts of them, it's typical for them to be fully rebuilt at the end of their useful life which yours doesn't appear to have reached yet.

Conclusion: unless you have specific reasons to need to remedy things right now, I would wait until your deck gets much closer to rotten/useless/unsafe and replace the whole deck, building everything in correctly. But only an experienced deck inspector on-site can tell you if you're already in "unsafe" territory, such as causing damage to your house or collapse hazards.

Edit to address additional information from comments: If a significant portion of the deck needs to be replaced (half rotten, half not) or replacing all of the decking with composite, bear in mind that structural components such as joists, beams and posts are typically not as durable as composite decking and likely to wear out earlier. This makes it even more important to ensure your posts, beams, joists are all up to code in order to maximize the life of your composite decking, which is fairly expensive (lumber crisis of 2020/21 notwithstanding). Even if only partially disassembling the deck, it would be a good time to deep inspect and fix components where you can; your deck inspector has probably already done this and recommended several fixes in this regard.

With this new information, it changes my answer so that I agree more with your inspector, but other readers may still find the original information useful.

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  • Thanks for your response @Fedric Shope. Would your recommendation change at all if I'm currently resurfacing the deck?
    – Joe
    Oct 1 at 15:45
  • I agree with this conclusion. When posts are rotting at ground level, joists are often rotting where they connect to each other, to beams, to decking, and to the home. Lifespans tend to correspond fairly well among components.
    – isherwood
    Oct 1 at 15:46
  • What do you mean by resurfacing? Staining/painting? Or replacing decking with composite? Oct 1 at 15:46
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    I wouldn't want to make such a call, and I doubt Fredric does either. Poke your deck in a bunch of places with a sharp stick. If you find any softness, that will help guide your decision.
    – isherwood
    Oct 1 at 15:48
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    Inspector (and myself) found no softness anywhere. Surprisingly, even with 4x4's right in the ground it's held up to decade(s) of maryland rain and conditions. There does seem to be good water management around the deck.
    – Joe
    Oct 1 at 15:51

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