I researched a lot of different ways & materials to build the hobbit house. I ended up going with the least expensive & least cumbersome option which was to do a typical stick build while transforming it into anything but typical. This is how I did it.
Once we carved into the mountainside we laid a layer of gravel & plastic on top of that to build our foundation on. Using 2×6 treated lumber on 12″ centers instead of 2×4’s on 16″ centers, we built our 24′ x 12′ structure which then was sheeted in 3/4″ marine plywood. That made for a crazy sturdy box! We wanted to make sure it would be able to support the amount of dirt that would eventually be covered in.
The next major concern was water & how to keep it out! Once the hobbit hole was buried it would be pretty close to impossible to fix a leak. I found the solution in Certainteed. We used Certainteed house wrap & ice guard around the entire house. Taping any seams & using there flashing on all the corners. I haven’t seen any flashing like this before it was sticky & stretchy peel stick saved tons of time.
We added a corrugated metal roof just to prevent any rocks in the soil from pin-pricking through just to be safe. We also came up with the idea of using straw bales as yet another barrier between the house and the soil. That accomplished a couple things, one it helped block any big rocks from slamming into the house as well as cut down on the amount of fill it was going to take. The last step was adding french drains all the way around the house & then it was ready to bury!!