The compression ring I designed and had built by a local machine shop for our earthbag roundhouse worked perfectly. It costs me just $20 or so and used very few materials. The roof bolted together in one hour and, as reported previously, it was rock solid even with 4-5 workers climbing on it. Also note, roundhouses are the fastest, easiest earthbag shape to build and this type of roof works perfectly.
So why did I make this new design? For one, the compression ring on our roundhouse required tricky bending of steel at an angle. See photo of the beautiful exposed ceiling. Some shops may not have the skill or equipment to make one like this. I wanted something simpler that anyone could build almost anywhere at dirt cheap cost.
I was admiring the beautiful roof on the Superadobeserano earthbag house. (Again, wow! Great job on the roof.) They used a log section instead of a steel compression ring. That works fine on small roofs, but what about larger roofs? And then there’s a risk of splitting, non-code compliance and the inconvenient center pole. So I set out to combine the best features of both.
The new design shown above seems to meet all my criteria. The emphasis is on simplicity. It’s just a steel cylinder with brackets welded on. Every metal shop or backyard welder in the world can make this if you can’t. There’s a vertical piece bent into a circle, and circular pieces of plate steel welded on top and bottom. Steel brackets with pre-drilled bolt holes are welded on to support the rafters. Fabricate and paint the compression ring in advance so it’s ready when it’s time to build the roof. Then all you have to do is drill holes in the rafter poles and add bolts.
Note, the drawing is to scale showing 16 – 3” poles (at the tip) bolted to a 16” diameter compression ring. If you use different size or number of poles, you’ll have to adjust the measurements so everything fits.
Also note you can build two of these roofs — one above the other — to create a Double Pole Roof with space for lots of insulation.