Another Post Footing Alternative

Concrete footing detail for wood, bamboo or metal posts
Concrete footing detail for wood, bamboo or metal posts

Many of our readers use post and beam frames for their natural homes and so it’s important to know various options for setting posts. I’ve been corresponding with Zafra, one of our readers and the lady who helped translate my Earthbag Building Guide into Spanish. She and her partner Daniel are going to use bamboo poles on their natural home in Venezuela, but the method shown here will work just as well with wood or metal poles.

The drawing is pretty much self explanatory. Here’s a quick overview and some suggestions for this low cost footing technique:
1. Fill 5-gallon bucket with concrete for footing.
2. Wrap the lower part of the post in plastic sheeting (the part in contact with concrete because concrete wicks moisture and will cause the post to rot).
3. Raise the post off the bottom about 4”-5” so there’s enough concrete to carry the load.
4. Fill PVC pipe around the post with concrete. Extend the pipe and concrete about 12″ above grade to prevent water damage (above 50-100 year flood level)
5. Plumb and brace the posts, then add gravel bag foundation on rubble trench.

Zafra and Daniel’s blog Casa Abya yala

10 thoughts on “Another Post Footing Alternative”

  1. I don’t trust plastic around the post if moisture gets in somehow it couldn’t get out 100 years ago or so they would roll the lower part of the post in a fire to blacken it to keep it from rotting. maybe some linseed oil would waterproof it

  2. Im planing a post and beam with earthbag infill (filled with perlite, im building in west virginia, very cold in the winter). I have been thinking about doing concrete posts, so do you all think that this example would work with just using concrete all the way up for the posts? as in instead of stopping the pvc at a foot or two above the floor line to take it all the way up to the roof. Could this work? of course the concrete posts would have to be reinforced with rebar…

  3. Interesting. To clarify: does the plastic that wraps the post extend to the top of the concrete infill? If so it must be tricky to get the concrete packed firmly in that cavity, while keeping the plastic extended above. (I guess that’s what duck tape is for!) But what a brilliant solution for avoiding rotting posts.

    • I forgot to say that this is primarily Zafra and Daniel’s design. Sorry about that. They’re in earthquake territory in South America and want strong posts.

      Yes, extend the plastic sheeting above the concrete and tape in place. I like to use 6 mil plastic — the same kind used under floors to prevent wicking and on the outside of earthbag foundations. Use PVC pipe large enough to place concrete inside. In this example we’re showing a 4″ post inside 8″ PVC. That’s just an approximate. This hasn’t been done yet to our knowledge, so do an experiment first.

      • I recommend a small alteration to the design.

        I recommend that the concrete poured around the post go higher than finished floor level. Think of it as a post “toe up.” (Kinda performing a similar function to toeups for strawbale walls.) Just a couple of inches higher than finished floor height should be sufficient.

        That prevents most plumbing leaks, or any other water from wanting to soak into the base of the post as easily. That extra couple of inches of concrete just around the post at floor level probably totals significantly less than an extra cubic foot of material per post (depending on the post diameter it may be a drastic amount less.) The amount of extra concrete is is insignificant (compared to the entire structure) in terms of carbon footprint, and monetary cost. Yet the protection that extra couple of inches provides is dramatic.

        This principle of building up the concrete around a post is not a new concept. It is standard practice when building fences and embedding them in concrete. The top of the concrete footer should be sloped away from the post to shed water away from the center in that application.

        Similar concrete build-ups are standard best practices in standard code approved concrete basement slabs where a lally column intersects a basement floor. That extra bit of concrete above floor level prevents water from pooling around the base of a steel column and rusting it out rapidly. Great protection for a long lasting structure.

        It’s an exceedingly simple design concept that could easily be applied in this design. for very nearly zero extra costs.

        • Good point. The edited drawing should show:
          – 3rd course of gravel bags (this raises the straw bales, earthbags, etc. well above the floor
          – a dashed line for floor level in the middle of the 2nd row of gravel bags with the concrete footer about 2″ above finished floor

          This and other low cost building ideas will eventually be part of the Wiki Natural House we’re planning. Discussions are ongoing and we’re making progress.

          • Another possibility. Particularly for wet climates or areas prone to flooding…

            Don’t embed the bamboo or any other organic post material down inside the concrete at all. Instead, make a short concrete post reinforced with rebar that extends a foot or two above floor height with rebar extending out the top of that concrete post.

            Then simply slip the bamboo over the top of the hardened concrete post, or drill a hole in the base of a wooden post to slip over it.

            That keeps all the organics up out of the ground.

            It’s also possible to use strapping instead of rebar sticking out the top of the concrete post that can be screwed to the base of the bamboo or wooden post after it is slipped over the top. This would allow the post to act as a tensile member helping prevent the roof from lifting off in high winds, as well as acting as a compression member to hold the roof up, and as a wall stiffener.

            Food for thought anyhow. There’s always multiple methods to accomplish the same goals. (Contrary to what many building inspectors tend to believe.)

          • Right, there are lots of options and the best choice partially depends on local conditions, what materials are available, etc. In this case, the owners are in a seismic area and want the strongest system possible. Also note, they don’t want to buy factory made hardware.

            Anyway, these little design discussions are interesting and thought provoking. Thanks to everyone who’s been sharing.

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