Q&A / 

Treated Wood Foundations

DEAR TIM: Several years ago, there was a movement toward the use of wood foundations due to the rising cost of labor and concrete. I toured a couple of newly constructed homes in the Toledo area at the time that had used this technique.

My question is "How have these structures fared over time?" Are they still considered sound and what has become of the idea of wood frame foundations? Are there any contractors using this method actively today? At the time I thought it a good idea, but being the skeptic I am I thought it was better left to someone else to prove the concept. I have built several homes over the years (for my own use) and have given thought to another project. Your thoughts and insight are always appreciated as I am an avid reader of your column in the Toledo Blade. Roger Puppos, Toledo, OH

DEAR ROGER: I absolutely remember that movement promoting wood over masonry for foundations. The thought back then that rushed through my head was the fable about the Three Little Pigs. As many of us know, the big bad wolf ate two of the three little pigs - the ones that used straw and wood to build their homes. The pig that used masonry was not harmed by the wolf.

My problem with the wood foundations was never one concerning engineering. I was convinced a properly constructed wood foundation could easily act as a retaining wall against all soil pressures that were trying to push it over. Wood shoring has been used for years to protect workmen who install piping in deep trenches and those who work in mines.

Lookie lookie, Can you see the extensive termite damage on the right side of the post? Imagine my reaction when I pulled this post out of the ground. PHOTO BY: Tim Carter

Lookie lookie, Can you see the extensive termite damage on the right side of the post? Imagine my reaction when I pulled this post out of the ground. PHOTO BY: Tim Carter

 

I have no doubt that the treated wood manufacturers still promote wood as a viable material for foundations. I also believe there are builders who still use wood for foundation work.

My real concern was long-term degradation caused by water and insects. The thought that kept playing in my head like an endless loop of video tape was an image of a workman at a plant that makes treated lumber. There were two episodes in this short documentary.

The first one was of the workman coming to work with a very bad head cold or the flu. In this episode, he starts to blend the chemicals that are used to preserve the wood, but because of his lack of concentration he makes a serious mistake and that batch of lumber does not receive enough chemical treatment.

The wood certified for wood foundations is supposed to contain a higher amount of the preservatives. That's a given. But how do you know if it does?

Episode two is a little different but the result is the same. The workman who mixes the chemicals goes and asks his boss for a raise. The plant manager tells the worker that he is not deserving of a pay increase. The disgruntled worker goes back to the work station and decides to take his anger out on the next load of pressure treated lumber.

I don't doubt for a moment that plants that make pressure treated lumber have quality control measures in place and follow them making sure mistakes don't happen. That is just good business. But mistakes do happen and I have proof.

The questions you have to ask yourself, since you can't easily test the lumber at your job site, might be:

 "Is the treatment in this lumber the correct mixture and will it LAST?"

"Was the lumber mislabeled?

"Was the correct amount of preservative used and was the pressure high enough in the vessel?"

In the early 1990's when CCA treated lumber was still being produced, I built a large play structure for my daughter. The main supports were 4x4 posts that I placed directly into the ground and backfilled with the soil. These posts were approved for direct ground burial. The treated lumber came with a lifetime warranty against rot or decay.

Fifteen years later, I took the play structure apart so I could build a large Queen Anne Victorian garden shed for my wife. To my amazement, two of the six 4x4 posts had significant termite damage to that portion that was buried in the ground. To say the least, I felt vindicated about my suspicion that treated lumber was not to be trusted 100 percent of the time.

When it comes to building for a lifetime, I have a tendency to lean on my college degree in geology. Look at the great temples, tombs and castles that are still standing in the world today. One thing they all have in common is they all are made from rock. The Great Pyramids are still standing after thousands of years as are temples in Central and South America. Europe has castles that are hundreds of years old that are still in excellent condition. Remember, concrete is nothing more than artificial rock.

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17 Responses to Treated Wood Foundations

  1. 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. 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. 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

    • 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. Tim,

    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,

    • Ralph,

      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. 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.

    • Mark,

      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'."

      • Tim,

        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. 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.

    • Carl,

      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. ...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. 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.

    • 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. 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. Hi,
    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,

    Heraldo

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