How To Build An Underground 

Hobbit House

That You Can Live In, That Will
Last 100's Of Years
The Concrete Foundation
The foundation was made in two parts , First a starter wall was cast on the exposed rock approx 3 ft high, no footing was used. The second phase of the foundation was the floor slab and center core (basement). A Block wall was constructed on top of the concrete slab between the split elevation.  One of the rules we used to design and construct the hobbit house was to be somewhat organic and keep the measuring tape use to a minimum. Even though the plan view is somewhat round you will notice in the photographs that the radius varies from very sharp to very gentle adding uniqueness to the geometry.  After construction one of the key performance factors not to have any settlement or shrinkage cracking of the concrete shell. After 3 years no cracking has occurred!

Starter wall construction
hobbit house concrete foundation underground home eco

Because of the curved nature of the structure 4x4 welded wire fabric covered with geotextile woven fabric was used as formwork. Easy and cheap. Blue electrical conduit was cast in to the walls for electrical service

Knee wall construction methods
hobbit house underground concrete foundation eco

The backside of the wall utilized wwf and geotextile cloth as formwork. the interior side of the wall used 24" wide plyform. Wall is cast directly on soil/soft rock. The wall will transfer the full load of the structure into the ground

Geotextile and WWF form back side formwork

Masonry Block Wall Placed Along Split Elevation
hobbit house underground concrete foundation

the concrete floor slab is separated by 30" difference between top and bottom. Also note the center core masonry structure. Inside the cylinder is a sub basement . the diameter is approximately 5 feet. concrete is cast to form the doorway arch in the block wall

Foundation wall at entrance

6" thick concrete wall cast directly on ground, mostly rock. 

Masonry Block wall
hobbit house construction underground concrete foundation

Center core masonry wall . Note elevation change between upper slab and lower slab.