Tuesday, March 19, 2013

Typical Rammed Earth Wall Section

Since I've been getting some questions lately, I thought it would be instructional to put up a section drawing of the rammed earth walls in my house so you can get a look at my engineering specifications.

In Canada, rammed earth construction is not covered by the building code, so any project requring the services of a building inspector will also require a structural engineer to sign off on plans that the building inspector cannot.

My footing goes down two feet for frost heave in this climate, and it's two feet wide. Multiply that by the perimeter of my building and that's a lot of concrete. I see the occasional bit of hand-wringing on-line about the piddling 5,6,7 % cement going into a contemporary rammed earth wall and I have to roll my eyes --that aint the least of it, son. 

Last spring I attended a rammed earth wall building workshop where a foot-thick, eight-foot long, five-foot high ( 6'x4'? my memory is hazy) block was rammed right on the bearing soil. No footing, no reinforcement, no damp-proofing, no roofing, and it is as crisp as the day it came out of the form after a long wet snowy winter. It hasn't fallen over and crushed a child yet either, though you can bet I will tell you all about it should that come to pass.

All that to say, this drawing might be on the excessive side of things when it comes to footings. I think more permitting officials and allied tradesmen should consider the Chew Kee Store and its walls that simply start two feet below grade, no concrete footing, cement stabilizer, steel reinforcement or damp-proofing barrier necessary, in Northern California, where they invented earthquakes.

My engineer specified rebar every two feet in each direction, which didn't seem excessive after the West coast projects I have seen (every sixteen inches, now that's a bit of a pain.) I wonder, though, if these walls would last longer (like, hundreds of years longer) without rebar in them. What if we are building walls that only last 500 years instead of 5,000?



I hired Blah Blah Engineering because when I spoke with Mr Blah he said, "Oh yes I'd love to do something with rammed earth, I studied it in the 70s and have even drawn up plans in the recent past." That is exactly the kind of confidence you are looking for in an engineer. You don't want a worrywort or someone unwilling to research. Otherwise, if you are in Seismic Zone 3 or higher and are looking for an affordable eco-building system, you might want to consider living on a boat or felting yourself a giant nest. By the time the permitting officials are done with you, all your money will be spent on insane re-inforcement schedules and giant concrete footings. And permitting officials.

This drawing and the rest of my plans were drawn by the incomparable Marshall Witzel at Aztec Drafting, who is a peach and you can tell him I said so.

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