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  1. #1
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    Default How long will these PT posts last?

    IMO, pressure treated wood is still wood and will eventually rot if buried in the ground.

    I told the client these posts might be ok for a while, maybe ten years even, but they will eventually rot and then this whole deck with a hot tub and a gazebo cover will be in danger of collapse, needs a proper concrete foundation. Was I out to lunch? (He decided to walk.)

    The cat wasn't scared, but he's got 7 lives.

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  2. #2

    Default Re: How long will these PT posts last?

    Pressure treated wood will rot, and does all of the time, but..........

    That doesn't mean that the pressure treated wood used for the deck was not rated for burial/ direct grount contact.


  3. #3
    Michael Schirmer's Avatar
    Michael Schirmer Guest

    Default Re: How long will these PT posts last?

    Most have have a 25 year wood-to-ground contact warranty. But yes, it is wood and will eventually rot.


  4. #4
    Join Date
    Apr 2008
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    Western Massachusetts
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    Default Re: How long will these PT posts last?

    Unfortunately most PT wood isn't stamped with the preservative and retention amount - it's on a little tag stapled to the end of the member. Therefore you usually don't know if it has been preserved to UC1/2, UC3A/B, UC4A, UC4B, or higher.

    Most of the big box stores sell UC4A posts which are good for ground contact, but not burial. My local supply shops sells UC4B posts (direct burial) and UC4C posts (severe conditions direct burial) that can be used for wood retaining walls or permanent wood foundations.

    So if the deck builder has done their job properly, they've selected the right preservative level for the job (UC4B minimum, UC4C preferred) and the wood foundation will last for a number of years. But what are the chances of that?


  5. #5
    Craig Werner's Avatar
    Craig Werner Guest

    Default Re: How long will these PT posts last?

    Bottom line, while the builder might have done it correctly and used the correct materials you can not prove it and without that proof you have to report conditions as you find them.

    I think you did it correctly , the only other thing you might have done was to have the buyer request proof paperwork from the seller.


  6. #6
    Join Date
    Feb 2009
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    St. Louis, Mo. area.
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    Default Re: How long will these PT posts last?

    Any time I observe wood support posts in direct soil contact, I call it out as a potential problem, but I usually stop short of predicting eventual collapse. With this steep slope, and the added weight of a hot tub however, I might have made an exception in this case. With those additional conditions, this needs to be as strong a construction as possible. As mentioned by others, you have no idea of the grade/quality of the posts. Furthermore, for all you know, they might only extend just a very few inches into the ground.


  7. #7
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by Michael Chambers View Post
    Furthermore, for all you know, they might only extend just a very few inches into the ground.
    A good point, which brings up the related issue of bearing surface when heavy objects (such as hot tubs filled with water and people) come into play. The soil must be such that it is able to bear the loads over the surface area, which is reduced when there is no footing used as part of the foundation system.

    Let's say the soil (assumed to be compacted) has a minimum bearing of 3000 psf (a safe assumption for the location although the slope raises interesting problems with soil bearing calculations). The end of a 6x6 post is .21 sf, meaning a direct buried post with no footing can support 630lbs in such soil. I counted 9 such posts in the picture (could have miscounted - kept falling into a trance when I looked into the cat's eyes), providing support for a total of 5671 lbs load.

    Now the smallest hot tubs I've seen have a "full" weight of around 3000 lbs. Some of the larger models easily hold 5000 lbs of water or more. The question then is whether anyone should feel comfortable with the load on the structure nearing the bearing capacity of the foundation system.

    For any such design there should be documentation that it was planned and constructed properly with both the correct materials sourced and detailed construction practices followed. Without that (and it's not necessarily the HI's job to look for that documentation - only to call attention to the need for such) any buyer should at a minimum be suspicious of the structure and discount its value in the transaction.


  8. #8
    Join Date
    May 2007
    Location
    Tyler, TX
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    Default Re: How long will these PT posts last?

    Personal experience: they'll last more than 15 yrs and even as pier/boathouse supports (under water). As far as the hot tub, that's a whole nuther ballgame.

    I've removed old posts from boathouses that were 20 plus years old (old CCA)

    Bruce

    Bruce Thompson, Lic. #9199
    www.TylerHomeInspector.com
    Home Inspections in the Tyler and East Texas area

  9. #9
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    Spring City/Surrounding Philadelphia area
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    Default Re: How long will these PT posts last?

    Whenever I see PT posts in contact with grade level, I probe the bases of the post at and beneath grade level with a straight slot screwdriver. Many times, rot is present in varying degrees from just starting to rot all the way up to full replacement needed.


  10. #10
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by JB Thompson View Post
    Personal experience: they'll last more than 15 yrs and even as pier/boathouse supports (under water). As far as the hot tub, that's a whole nuther ballgame.

    I've removed old posts from boathouses that were 20 plus years old (old CCA)
    What is equally, if not more important than the type or preservative is the different preservative retention levels. CCA-C is a very effective preservative and is still used for "listed" purposes, including dock piles and permanent wood foundations. However some of the newer preservatives are also suitable for wet service - the preservative used and retention amount depends on the environment where the wood will be used.

    For salt water environments the pile will be treated to UC5A, UC5B, or UC5C, with the 'A', 'B', and 'C' referring to northern, middle, and southern coastal areas respectively. For fresh water environments, a pile treated to UC4C may be specified. Unfortunately, many builders don't know the difference and just grab whatever wood is marked "pressure treated" whether it is suitable for purpose or not.


  11. #11
    Phil Brody's Avatar
    Phil Brody Guest

    Default Re: How long will these PT posts last?

    Any guess by looking at them is just a guess, perhaps a reinspection schedule for integrity could be a suggestion.


  12. #12
    Join Date
    Feb 2008
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    High Point, NC
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by John Kogel View Post
    IMO, pressure treated wood is still wood and will eventually rot if buried in the ground.

    I told the client these posts might be ok for a while, maybe ten years even, but they will eventually rot and then this whole deck with a hot tub and a gazebo cover will be in danger of collapse, needs a proper concrete foundation. Was I out to lunch? (He decided to walk.)

    The cat wasn't scared, but he's got 7 lives.
    I can't agree with your analysis of the deck posts and a prognosis of 10+/- years of service before collapsing. You stated that the posts were PT; however, the posts in the left side photo have the appearance of being cedar, not pine. Cedar will certainly last much longer than PT pine. In addition, if the PT posts are well drained at the surface, and there can be no doubt about that, there is less risk of moisture leaching out the preservative over time which is the real cause of rot in PT posts.
    If the building code allows for PT posts to be set on a pre-cast or cast-in-place base and held in place with the soil around the post hole I can find no reason to say anything more about deck posts. All the speculation of what level of treatment has been applied to the posts cannot be determined in most cases by the seller and, in this placement, doesn't change my analysis in any case. If the buyers walked solely because of your comments regarding the buried posts I'm sorry for them. If, on the other hand, you have building codes in your area that require the posts to be elevated above soil grade I stand corrected. In NC, I have no problem with what you have shown in the photos.


  13. #13
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    Aug 2009
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    Michigan
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by Tom Edwards View Post
    I can't agree with your analysis of the deck posts and a prognosis of 10+/- years of service before collapsing. You stated that the posts were PT; however, the posts in the left side photo have the appearance of being cedar, not pine. Cedar will certainly last much longer than PT pine. In addition, if the PT posts are well drained at the surface, and there can be no doubt about that, there is less risk of moisture leaching out the preservative over time which is the real cause of rot in PT posts.
    If the building code allows for PT posts to be set on a pre-cast or cast-in-place base and held in place with the soil around the post hole I can find no reason to say anything more about deck posts. All the speculation of what level of treatment has been applied to the posts cannot be determined in most cases by the seller and, in this placement, doesn't change my analysis in any case. If the buyers walked solely because of your comments regarding the buried posts I'm sorry for them. If, on the other hand, you have building codes in your area that require the posts to be elevated above soil grade I stand corrected. In NC, I have no problem with what you have shown in the photos.

    I couldn't agree more. I have seen many pt post and wood basement foundations last for years. If the right retention of .60 is used and proper placement and treating any cuts properly, wood provides a very stable foundation. Guessing of a collase just because it's wood is a bad idea, especially if the prospect walked because of it. Mention it in your report and let him verify it with an engineer, but don't scare him off.

    Randy Gordon, construction
    Michigan Building Inspector/Plan Reviewer

  14. #14
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by Tom Edwards View Post
    I can't agree with your analysis of the deck posts and a prognosis of 10+/- years of service before collapsing. You stated that the posts were PT; however, the posts in the left side photo have the appearance of being cedar, not pine. Cedar will certainly last much longer than PT pine. In addition, if the PT posts are well drained at the surface, and there can be no doubt about that, there is less risk of moisture leaching out the preservative over time which is the real cause of rot in PT posts.
    If the buyers walked solely because of your comments regarding the buried posts I'm sorry for them.In NC, I have no problem with what you have shown in the photos.
    Thanks. Lots of good comments, and varied opinions. The posts have a cedar stain applied to them, but they are PT, you can see the machine marks on them. I've seen cedar fence posts rot in less than 10 years in this climate, so yeah, there are regional differences.
    For the record, there were issues with the foundation of the house, relating to the steep slope. The deck was not the scary issue here, but I brought it up for discussion anyways.
    I recommended an upgrade to concrete piers for this deck. Hey, that's just my opinion.
    I discussed the posts verbally with the client, stating that the lifespan was unpredictable. I don't recall using the term "collapse" at any time, but pointed out that the weight of the structure and hot tub is considerable. Stuff like that. Thanks everybody for your input, and Happy Holidays!


  15. #15
    chris mcintyre's Avatar
    chris mcintyre Guest

    Default Re: How long will these PT posts last?

    I have seen my share of rotten cedar and PT post that are less than 10 years old in this area.

    If the right retention of .60 is used and proper placement and treating any cuts properly,.......
    DG, while agree that this is true, as an inspector surly you will admit that this would be the (rare) exception and not the rule.

    Throw in the weight of the hot tub along with the slope, I believe not to warn the client of the potential danger would be wrong, in this case.

    The cat wasn't scared, but he's got 7 lives.
    John, I thought they had nine lives? Did you run over him a couple of times on the way in? That would explain it hiding under the deck.


  16. #16
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by chris mcintyre View Post
    John, I thought they had nine lives? Did you run over him a couple of times on the way in? That would explain it hiding under the deck.
    Old cat. Ok for a soup, maybe, but too old for cutlets.

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  17. #17
    Join Date
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    Default Re: How long will these PT posts last?

    Quote Originally Posted by chris mcintyre View Post
    I have seen my share of rotten cedar and PT post that are less than 10 years old in this area.



    DG, while agree that this is true, as an inspector surly you will admit that this would be the (rare) exception and not the rule.

    Throw in the weight of the hot tub along with the slope, I believe not to warn the client of the potential danger would be wrong, in this case.



    John, I thought they had nine lives? Did you run over him a couple of times on the way in? That would explain it hiding under the deck.
    Your right Chris, most stuff stuck in the ground shouldn't be. I do agree with warning the client, but not saying it's bad just because it's a wood foundation.

    After reading Johns last post, I also think he handled it well also... good work John.

    Randy Gordon, construction
    Michigan Building Inspector/Plan Reviewer

  18. #18
    Join Date
    Dec 2009
    Location
    NJ
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    1

    Default Re: How long will these PT posts last?

    How long should my UC4B posts last? They're 10ft posts barried 4ft deep in concrete. The concrete is flaired at the bottom to minimize shifting/ sinkage and have several inches of gravel at the bottom for drainage. They're being used for a fence. Will staining/sealing have much effect on their life span.


  19. #19

    Default Re: How long will these PT posts last?

    Will staining/sealing have much effect on their life span.
    Not in my experience. The middle section of the posts will rot out where buried/ set in concrete.


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