Treated Wood Foundations

19 responses

  1. Laura
    January 25, 2013

    Dear Tim. I just read your reply back to roger and it answered most of my questions. I'm am currently looking at purchasing a house with PWF and it was built in 1977. I guess a couple Of questions would be how hard/expensive is it to replace a PWF and what is the life expectancy is on a PWF

  2. arnold
    July 16, 2013

    sounds like Tim might be a masonery contractor. I built a 7 bed room log housr 30 years ago and its still as new. a 30 year block or concreat basement will have cracks, dampness, musty, etc.

  3. Lenny Rutledge
    August 4, 2014

    I am the Building Official for the City of Hutchinson, Hutchinson MN.
    I have been on the job for 15 years and have never seen a wood foundation constructed. However I live in a home with a wood foundation.
    I have been asked by a builder how to insulate a wood foundation for a slab on grad home. Our area requires 42 inch frost protection.Can you help us with insulating the foundation wall?

    Thanks, Lenny

    • Tim Carter
      August 5, 2014

      I'm so confused. Why / how can a slab-on-grade home have a wood foundation? I would think they would do a turned-down concrete slab or pour a footer / foundation, backfill and then pour the slab on this. Lenny, what am I missing?

  4. Ralph David
    February 25, 2015


    I am looking at a home with a wood foundation, I can see that the walls are bowed in and several studs have moved in 1/2-3/4" in along the slab do to freeze/ thaugh in Michigan. Where basement windows were framed studs are pushing in under window where there is a break in the top plate. Is there any way to stop it, is this a sign of failure.

    Thanks for your input,

    • Tim Carter
      February 26, 2015


      RUN AWAY from this house. You never EVER want to purchase a home that has significant STRUCTURAL issues. On a scale of 1 to 10, with 10 the worst, I'd rate what you say about a 8.5.

      You couldn't GIVE me a house that has an issue like this. To fix it, you'll be calling up the companies that move houses to lift yours up. Then you'll RIP OUT the crappy wood foundation and pour a proper poured concrete foundation.

      Now, if you've got a rich auntie or have won the Powerball lottery, then have at it!

  5. Mark
    May 12, 2015

    I am a builder and have put in 12 homes with PWF's. I've lived in one of them for the past 18 years. I am planning a new home with a PWF and would never live in anything else. A PWF must be designed by a Engineer and installed properly or it could have problems. The post on your "Queen Anne Victorian garden shed" was a post from the Depot not foundation grade wood, any wood from Depot is not rated for ground contact and will fail. You can do a PWF with a slab on grade.

    • Tim Carter
      May 12, 2015


      The lumber from my Queen Anne shed was not purchased from a big box. It was purchased from the top lumber company in Cincinnati that sells the MOST and highest-quality treated lumber. It's the best you can buy.

      The photo in this column tells the tale. Treated lumber APPROVED for ground contact EATEN by termites.

      You can't argue the fact that quality control can slip one day and the wood you THINK is okay is not. Since you don't have a field testing lab, you HOPE the wood you're using WILL last.

      But as Kenny Chesney said in his hit song, "Only time will tell, but it ain't talkin'."

      • Clyde Steele
        May 12, 2015


        I'd suggest that the question isn't whether or not a wood foundation can fail due to a manufacturing defect, but rather what is the frequency of failure due to material and/or installation problems vs. a typical masonry foundation, and what is the cost to repair the foundation if it does fail? Your thoughts?

  6. Carl
    May 12, 2015

    Mark is correct. Permanent wood foundations use FDN treated lumber. Pressure treated wood rated for ground contact is not to be used for foundations. The preservative chemical retention for ground contact wood is less than that of FDN treated wood. In addition the wood used in PWF does not contact the ground. There must be a water barrier between the dirt and the wood. Check your codes. Also check out the Scandinavian Countries. They have been using PWF for many decades.

    • Tim Carter
      May 12, 2015


      I know. I believe you missed the point of the column. How do you know for certain the wood has the correct amount of preservatives, even if it's stamped FDN?. You can't test it in the field. Maybe a batch was STAMPED wrong? It wouldn't be the first time mislabeled goods entered the marketplace.

  7. Carl
    May 12, 2015

    ...or misbatched concrete or improperly mixed mortar or...

    Usually the failure of pressure treated wood is bad design, improper materials, and/or inappropriate fasteners.

  8. Wayne Anderson
    May 12, 2015

    You can raise the same issues with concrete as with wood. How do you know that your concrete is mixed correctly? I have a friend who is a mason he has had numerous problems with bad concrete mix from several suppliers that have had to be torn out and redone.

    • Tim Carter
      May 12, 2015

      That's true. But you can fairly easily have two test cylinders taken of the concrete and have them tested within a week. That one-week test will tell you if the concrete will achieve its design strength.

      The entire point of my above column is to simply show that wood is not a permanent material and that I have proof of a failure of the preservative.

      It's a simple statement of fact and I do that so that others can make an informed decision.

      Here's the other way to look at it. If wood was such a good idea for foundations, why is it you don't see it more often? Why isn't it the industry standard?

      These are simply rhetorical questions and the marketplace usually makes the decision.

  9. Walter
    May 14, 2015

    I am a residential remodeler/builder in northeast KY. I will add a few facts I've learned over the years to this conversation. That being said I would not have the confidence to use a wood foundation myself. Even when we build a deck or sun room that has a patio underneath I pour concrete footing with concrete piers up to grade and then attach posts with proper hardware.
    1. You said 2 of the 4 posts had the termite damage shown in the pic. I wonder if they were cut ends. They sell the preservative at most lumber yards to treat the ends of a post if you are putting the cut end in a ground contact situation because the center of a thick post doesn't get treated very well at the plant where it's produced.
    2. I had a conversation with a man that sells for one of the largest "Pole barn style" metal building companies in the nation and asked about problems with post rot and was surprised to find out they still use CCA treated lumber. It does seem to be better preserved than the more common ACQ and MCQ products we buy today. Apparently since they're work is deemed commercial they can still use it. It was only banned from residential work. I wonder if it can still be used for foundations?

  10. Heraldo
    August 20, 2015

    I'm doing a addition to a existing house. The general contract built on the top of the foundation a frame (PT) to fix the height of the foundation. He used am various frames sizes, 2x6, 2x10, now he is adding a concrete slab and it will touch the frame that he built. My question is. Can the concrete touch the pressure treat (PT) wood?
    I really appreciate your answer.
    Thank you,


  11. George Arrowood
    April 7, 2016

    I am thinking of a wood foundation and my question is, would it be acceptable to treat the outside with a tar base like they do with concrete or block, beofre you put on the plastic barrier?

  12. Cory
    November 1, 2016

    People looking for more I do should go to the southern pine council website and search for wood foundations, they have a nice pdf download for free that includes details for free.

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