Digging and building a CBU basement foundation

This spring we are breaking ground on the foundation basement for our log cabin home. We’ve decided to used CBU’s instead of forms due to availability and the ability to build incrementally. Due to the crazy housing boom in north Idaho we have been unable to find a consultant to advise us on starting the project. So I’m reaching out to tap the global knowledge here.

If you have any books, websites or other information please don’t hesitate to share.

We are excited about this build. We have been living in an insulated “high tunnel “ on our homestead for 5 years.

Maybe if I were in the building profession I would know what a CBU is.

When I put in "cbu forms for log cabin" Mr google insisted that these are forms to fill out to go to a college.

When I asked the forum's search function the only thread was this one:

https://permies.com/t/16304/wood-ash-soil-cement

Maybe this will help or someone with knowledge will chime in.

My guess is concrete masonry unit (CMU), aka concrete block, aka cinder block ... both of which could then be called "CBU". Is the attached pic similar to what you're after?

Key issue might be knowing exactly what kind of dirt you've got, and what the locals (local foundation folks) do about it. Another issue is codes in your area ... my area required an "engineered" foundation plan.

Search for "cmu foundation section detail", or some combination thereof. Also, search for "log cabin" books, all of which discuss "typical" foundations, and include CMU sectional details for foundation and CMU wall.

And then get an engineer ...

Did you rule out ICF's? Something like 2nd attached pic?

We decided on the block foundation since it’s built incrementally rather than all at once. Expenses can be stretched over the summer along with our labor availability. I’d love the ICF foundation. It’s just a big chunk of capital all at once.

We don’t have codes out here just a location permit so they can tax us on the improvements we make with our own money.

What is the name or type of engineer I’m looking for?

Any licensed Professional Engineer (PE) in the area, familiar to the code departments and builders of that area.

If you have to put in a septic system, then use the perc test hole to get an idea of the kind of dirt on your property. If no septic system is required, try to get a (backhoe) trench dug in the area of your foundation, so an engineer would have an idea of the kind of dirt you've got.

If, however, you are really code-free in your area, then you can skip the engineer and find a good foundation plan on the 'net, along with sections and details that are similar to what you want to do. You'd adjust these to the actual conditions you find when excavating your dirt.

Or, even better, get an idea of what you want to do, and run it by the PE in your area ... while not as specific as having bore holes or other test results of the kind of dirt at your location, the PE will still be able to keep you out of the weeds ... if he/she stamps the foundation plan, even better. It was a few hundred dollars to get an engineered/stamped plan from my local PE, and that, more than anything else, was what my code department cared about.

Hope this helps ...

I think you will find a true block foundation is NOT considered  good building practice.  You can build a block wall on top of it but that your footer needs to be poured concrete.  The reason is they want a solid beam under the block to keep it from racking, lifting or settling in areas etc.  Block walls do very poorly under these conditions so the goal is to set them on a solid beam so hopefully they move as a unit reducing cracking.

One comment is you will likely want to pour some of the cores full of concrete.  Lesson learned from the 2 builds we did with block.  On both later holes punched thru the walls for water lines etc show we failed to get the concrete to the bottom of the hole in ever single hole we punched.  So if you pour cores be sure you are using flow enhancers in the concrete so it makes the bottom of the core.  A long stem vibrator might help too.

The other comment is waterproofing the block is critical for long term life expectancy.  I think I would go for multiple layers of it.  At least a paint on elastomeric membrane, sheet insulation and top that off with a swedish skirt insulation to help carry moisture away from the building under ground.