using tree stumps as a foundation

So I'm driving down the road today and I see in someone's yard a kid's fort built on top of a tree stump that is six feet high or so and it got me thinking...

The one part of building that I am constantly struggling with is the foundation. I don't like to use concrete if I can avoid it. So, I see this awesome fort and think, "Why not?" I am trying to think of any drawbacks to using the stumps, from some hard maple and black birch I am in the process of clearing, as the foundation for a small outbuilding. Other than the typical drawbacks to building on piers what else is there? Will they rot out too fast? Large stumps seem to be solid for quite some time and these would be protected from direct exposure. The idea of building off of them at 4 or 5 feet above ground and using the trees placement to guide the design of the building seems intriguing and fun to me!

Any thoughts?

Thanks,

Rob

Better to keep the tree alive. Wood does rot naturally so this may be good enough for a tree house but unless you want a home to last roughly a decade than you need to have strong foundations.

My wife lived with a guy for nine years in SC in an old cabin that was built on stumps. My sense of it was the cabin was very old. I would think if the stumps were of a rot-resistant species, like cedar, locust, or cypress, they'd stand a good chance of lasting as long as the rest of the structure. Remember there won't be nearly as much moisture up under there once a building is in place....

Sounds pretty ideal actually, but rare to find a perfect situation. Maybe if there was a grove of old trees or someone had planted a row of trees in a line, then you could have 4 in more or less a square. That would be pretty epic. A home build on 4 perfect stumps, made from the wood of those trees. In reality though it would be better to leave the trees growing and either build around them if you wanted to incorporate them, or build so you have a great view of them. I hear you on the concrete/foundation thing, its the one area that it's hard to get away from.

Interesting. We just looked at an old farmhouse in NC built in 1920 that has 2 locust stumps in the crawlspace, as part of the foundation holding up the 2 story house.

They seem in fine shape to me, but it does give me pause for a number of reasons... I was wondering if anybody had seen this sort of thing before, and whether or not we should look into updating them. Im leaning toward yes.

Thanks for the replies and the interesting thoughts!

The concept would definitely make the most sense with rot resistant species but I've got to work with what I have. The trees have to come down anyways to allow more southern exposure for growing more food and will be replaced with fruit trees planted nearby. So I may just build a funky chicken coop a few feet off the ground and see what happens!

This did get me thinking more about foundation alternatives though and I am thinking what if I just use rot resistant timbers on a compacted gravel bed ( taking into account the normal precautions regarding drainage, etc.) and build off them. I could design it so the timbers could be replaced with relative ease. Just thinking out loud...

jay william wrote:Interesting. We just looked at an old farmhouse in NC built in 1920 that has 2 locust stumps in the crawlspace, as part of the foundation holding up the 2 story house.

They seem in fine shape to me, but it does give me pause for a number of reasons... I was wondering if anybody had seen this sort of thing before, and whether or not we should look into updating them. Im leaning toward yes.

Isn't it amazing how ideas and solutions people used to build with, that may seem a bit crazy, can withstand the test of time? I love the barns here in VT that are standing on dry stacked stone piers that seem way too small to be holding up such a large structure!

If they still look good, you could always leave them and add other supports. Just a thought!

Saw this old thread and had a few ideas. Why not cut off the trees to the desired height and drill 4-5 1" diameter holes straight down into the stump about a 1-2 feet deep. Make up a solution of borate and polypropylene glycol and fill them up. If the tree was alive when cut, the pathways from roots to the trunk will be fully active. The solution should seep down into the roots with time. Since the building above will stop most of the exposure to water, there should be minimal seepage of the borate from the now preserved stump. Strip the bark with a power washer and surface treat the stump. You could even provide copper or stainless metal tubing which would be hammered into the holes for periodic addition of more borate solution. The metal tubing would be installed too high and cut off flush when the final flooring was installed.

I lived at a place that had a 25' x 25' two-story house that was built on tree stumps. After ~20 years the stumps rotted and the building collapsed.

Hi Abe,

How were the tree stumps treated in that 2 story house? If they were untreated, as I suspect, 20 years shows this could be a promising building technique. The studies of untreated vs. treated wood posts in Mississippi and Oregon show about a 10 fold increase in longevity. That's the main problem with new building techniques. In order to get a good idea of utility, a lifetime is usually required. By the time you figure out if it is viable or not, you're dead.

John

Jp Wagner wrote:Saw this old thread and had a few ideas. Why not cut off the trees to the desired height and drill 4-5 1" diameter holes straight down into the stump about a 1-2 feet deep. Make up a solution of borate and polypropylene glycol and fill them up. If the tree was alive when cut, the pathways from roots to the trunk will be fully active. The solution should seep down into the roots with time. Since the building above will stop most of the exposure to water, there should be minimal seepage of the borate from the now preserved stump. Strip the bark with a power washer and surface treat the stump. You could even provide copper or stainless metal tubing which would be hammered into the holes for periodic addition of more borate solution. The metal tubing would be installed too high and cut off flush when the final flooring was installed.

My personal thought is that if I have to dump chemicals into the tree stump, especially in an ongoing basis, I would rather just use concrete to begin with.  I know it will work and I don't want to add another chore to my already too-long list.

Jp Wagner wrote:How were the tree stumps treated in that 2 story house?

They were untreated, as far as I know.

I am not so sure about this.

I fuss with a lot of stumps, and get to know them pretty intimately, so my question is: How many people have tried to use stumps as a foundation and failed?

That may seem like a negative way of looking at stumps, but this is your foundation, get it wrong and you got an expensive mess upon your hands. I suspect a lot of people have tried using stumps as a foundation, just because it was easy, and many people like to take the easy way out. So I suspect a lot of those buildings that tried to use stumps as a foundation, are no longer in existence.

Another way to look at this is: What is so offensive about concrete?

I just posted the question, "What is so vile about concrete", and the collective answer shocked me. Really nothing; according to the replies upon Permies. I suspect the real issue with concrete is the cost. I fully understand that, I am as frugal as they come, but I make my own high strength concrete and save about half over what it costs to have a ready mix truck deliver it. That is because I just buy the portland cement, and this is something anyone can do. I typically use gravel because I happen to have some, but it is not required. Earthcrete has a higher probability of surviving over that of a tree stump a a foundation in a building. And if you do buy gravel, 14 cubic yards delivered to your house will cost you $150. That means a 4 bag mix of real concrete will cost you about $50 a cubic yard compared to a Readi-Mix Truck at $130 a cubic yard.

But a person could also go with a rubble-filled foundation, for the cost of an excavator rental which is $450; delivery included. And there is something to be said for building upon rock, as the Tiny House I live in now was built in 1930 after the first house here burnt. The foundation has been in place since the year 1800, making it 219 years old, and it has not moved. Even at 89 years old, the sills in this Tiny House are rot free.

I don't know how long one would last if it were kept dry, but big elm stumps here, at least 3ft round rot out in under 10 years. there were some at my old place around 5ft tall that had been left and at 8 years I could push them over by hand (and did)

I was about to say "they'll rot" but then it occurred to me that I read somewhere that Ely Cathedral is built on Elm pilings.

Our first home was built on bodark posts.  "Osage Orange"

The bodark tree (Maclura pomifera) is a common tree in Arkansas, known to live in at least forty-seven of the state’s seventy-five counties. The name “bodark” is a slurring of the French “bois d’arc,” meaning “wood of the bow”—a reference to the Osage Indians’ practice of making bows from the tree.

Source

Hi Everyone,

Thanks for all the input. My only thoughts on concrete are that it's not near as long-lived as people think it is. The Pantheon in Rome is a great example of how long un-reinforced concrete will last. NACE recently calculated the cost of corrosion to be 2.5 trillion dollars annually. Unfortunately a lot of that corrosion is inside concrete. As a society, we have gambled on the undying strength of reinforced concrete. We have been stupid enough to put normal carbon steel in most of our concrete. If we had used 304 or 316 in all of our structures we wouldn't have the crumbling infrastructure that we have. Studies show the addition of stainless rebar over carbon steel only adds 15-20% to the initial cost but dramatically increases longevity. We have kicked the can down the road again to our children and grandchildren.

I was thinking, for rural applications, a good sized shed could be put on top of treated stumps and built for practically nothing. So what if the shed becomes unstable after 30-40 years? They are pretty much disposable anyway. I certainly wouldn't use it as a foundation for a house, at least not until many sheds have been built so we see what happens. There is a lot of incentive in the capitalistic society we live in to suppress any change from building codes. Building codes are necessary but they are also written by engineers, architects, construction firms, lumber suppliers, and politicians on-the-take. They all have a vested interest in staying in business and making sure houses are built at $150 a square foot, or more.

My vote for the cheapest foundation is a rubble trench with integral French drain. All the benefits of concrete plus drainage and no steel to corrode. Build with a PWF superstructure using .6lb CCA for the footings and maybe the first 2 feet of walls. If building underground you can either use a wood floor or 48" galvanized mobile home auger anchors for lateral thrust with the full height of walls made from CCA lumber. There are lots of ways to build without concrete and not have to dig holes and have the rebar rust inside causing failure. Just remember that concrete is porous, not only to water but to air. You mix air, moisture, and iron and you eventually will have a serious problem. Iron oxide takes up more space then the iron it replaces. The expansive forces are immense and will destroy ANY concrete, no matter how strong it is.  

I like concrete because I have a gravel pit and thus can make it myself for very little money, and also because I REALLY love radiant floor heat. Granted a person can, and I certainly have, used other media that concrete to help transfer heat to the building, but concrete is so cheap because it becomes your foundation, heating system, and floor all in one cheap, easy for form mold. It also adds a lot of geothermal heat to your building, saving me money, not just in construction costs, but every year the building is heated.

But I also like the Rubble Filled Foundation. We used to be a potato farm from 1838-1988, so we have these areas we call "potato rock piles" It is where the rock came off the potato harvesters, and they are rock about potato sized naturally. These are perfect for French drains and rubble filled foundations. We have even used them for leach fields before because the water just pours through those clean, 3-4 inch rocks. I just did a trench with the backhoe or excavator, put in some drainage pipe, then haul down a few loads of that potato rock. We have had these leach fields still working and they were put in in the 1970's when I was a kid.

We even had a field that had a massive sag in it, and the water would collect there, and the tractors would get stuck. To cure that we took dynamite, and blasted a trench across the field in this sag. Then we hauled in potato rock, then pushed the dirt back over the potato rock, but deeper than plow depth. It is one massive French drain basically, but has been working for decades, and only took a few days to install.

But use what you got, that is what I have always said.

But I do apologize, in terms of using stumps I THOUGHT you meant use them for a house or something. Oh heck yeah, for a shed, they would be fine. I was just thinking a person would clear a forest to build their home, and just set them on top of stumps just so they would not have to try and dig out the stumps. I did not think that was a good plan. But for a shed, heck yeah!

No apologies necessary at all.

I simply don't know if a stump can be treated in-situ and what effect it would have on its decomposition. The only way to find out is to do it. The problem is I'll never be around to see the final decomposition if it takes longer than 30 years.

Wanted to post (albeit far from the original post date in 2019 but just now seeing) - that we have a house built in 1901 on Locust Tree posts in NC.  When we had it inspected 14 years ago, they raved about how great they were.  Just yesterday, we had a contractor, who we are talking with about an addition, rave about how sound the old two story house is and how impressed he is by no sagging or foundation issues.  🤷‍♀️  Just had to share since it seemed pertinent.  

Many medieval stone buildings and bridges were built on wooden pilings. The secret of their longevity is that they have been continually waterlogged. The drying/wetting cycle allows rot to proceed as fungus, mold and bugs can get in and live there. If oxygen is excluded, most things cannot colonize the wood. The other alternative is extreme dryness so there is no water in the wood to support life, but you need an environment like the Egyptian desert for that.

My daughter bought a circa 1890 farmhouse in northwestern SCwhich is built on 4 oak stumps and major floor beams are the trunks of the felled oaks. Building is in great shape and no sagging.

What is the situation of that building? Is it on a high, well-drained spot? I could imagine oak lasting a long time in conditions which kept most water and wicked moisture away from it.

When I was a child, I could still see the outline of a stump about 5 feet in diameter in the back woods, and 10 feet or so away the shell of the bottom quarter of an oak log matching it. I believe those were from the first settler who cleared the land in the very early 1800s, used the best log from the tree, and left the rest to rot because there was more than he could use. So oak can last a long time... 150-170 years in this case.

There was also a stump fence, tree stumps uprooted and placed in a line, obviously from the original clearing too. It was no longer an effective fence, but still a large and noticeable feature.

Hey Rob, I had a similar question a while back.  Maybe you'll find some other helpful info there.

My mother owned a house that was set on tree stumps.  It is still standing and has to be over 100 years old.

Travis Johnson wrote:I am not so sure about this.
But a person could also go with a rubble-filled foundation, for the cost of an excavator rental which is $450; delivery included. And there is something to be said for building upon rock, as the Tiny House I live in now was built in 1930 after the first house here burnt. The foundation has been in place since the year 1800, making it 219 years old, and it has not moved. Even at 89 years old, the sills in this Tiny House are rot free.

any links, resources, or instructional systems about how to build a foundation this way?

also the big deal about concrete is that it's carbon footprint is humongous and is in the top 10 list of project drawdown for most urgent/impactful steps to reduce our carbon footprints

Here is a different twist on subject.  I own a small cabin with a concrete foundation.   we want to add an addition to the west side of cabin facing a lake.  we have 2 25ft sugar gum trees that would need to be removed if we  extended foundation.  The shade these trees offer is not replaceable.   Has any one ever tied into a tree using equipment used to build lavish tree houses.  what is your opinion, think it would hold up.?

I don't know how rot-resistant sugar gum is, but trees 25 feet tall don't sound like they would be big enough to be a reliable support for the long term. I presume the actual outline of the addition you want would not overlap the tree trunks and branches so much as to require cutting them significantly, so I would put in some piers wherever you can avoiding the tree roots, support a solid beam with those, then build the addition floor framing on the beam. How far above ground is the cabin floor level in the addition area?

Here in Texas Bois Dark trunk sections are common on older houses because the clay soil moves so much.  Building like that made it easy to relevel the houses.  The trunk sections are hard to come by but kept dry many have been standing for 100+ years and are still going strong.  My great grandmothers house is approaching the 200 year mark.  We releveled it 4 years ago and that house is doing just fine.  We keep the roof, the gutters, and the cypress siding is good shape.  We keep lead flashing over the windows up and she's still warm and water tight.  We did have to patch some of the plaster inside (lath and plaster walls) when we leveled the girl up again, but that was it.  

It was common practice when building a house to plant more trees to use as replacements so if you look around you will often find a bunch of them planted in an overgrown grove.  Nothing eats bois darc though.  Even termites won't touch it unless its been wet for a really long time.  It is so hard that just pruning one will kill a few chainsaw chains (yes multiples sharpened so much they are just done).  

To revisit this idea:

I just had a huge 5 trunk red oak tree cut down. My plan is to keep a 7ft tall section of the trunks as a base to build a tree house on top of. The base of the trunk is about 6-7 feet in diameter.

I’m sure the trunk will eventually rot, but I’m thinking a huge solid 100 year old tree trunk will take 10-20 years to rot enough to become unstable holding a fairly small light treehouse structure. Any thoughts on safety and how long this could last? I only need it for at most 10 years for my child to use it.

Jonathan said," Any thoughts on safety and how long this could last?

You mention 7 ft so does that mean that you are building the treehouse 7 ft off the ground on an existing trunk that is in the ground?

Termites?