Using earth bags for building a Storm shelter

Since I live in an area that sees Tornadoes fairly often (2014 was the last one) I have been trying to find a building system that will not require concrete for the structure.
Our land is from valley to valley over one of the Boston mountain ridges and bed rock in places is about 2 feet below the surface.
I have been thinking of using this shallow bed rock to our advantage for building a combination Storm shelter/ root cellar for the underground portion.
What we will need to figure out is what will be the best building type for the above bedrock portion.

Our main focus has been on earth bag construction with perhaps a double wall set up for "missile" deflection.

Mr. Hart, as one of the recognized experts in this type of building, will you give me some ideas.
I look forward to reading your book, I know it will be a huge help and great addition to our library of references.

Redhawk

Hi Redhawk,

I think that your focus on earthbags as an approach to building this is good. They are one of the best ways to build underground because they are generally unaffected by moisture issues and can provide very strong retaining walls. There is a good reason why they have been used by the military as barricades against "missiles". You could place the earthbags on top of the bedrock as your foundation.

Reinforced concrete is often used to fashion a bond beam on the top of walls to help stabilize them and provide a good connection point for the roof, but it also possible to make the bond beam with wood or metal, as explained in the book. Cement is used sometimes to stabilize earthen plasters on the exterior, but you can also use lime to do this.

Thank you so much Mr. Hart, for this project I am not against using concrete, just didn't want to have to wrestle with a huge amount of it.

Would an Oval dome be a good choice for roof design in your opinion?
We plan on using a barrier for earthen roofs over the roof and doing a soil cover with grasses to hold the soil in place and make the structure fit into our farm landscape better.

forgot to mention that I will probably be using feed bags for this project since we have collected quite a few of them over the last two years of having AGH.

Redhawk

Oval domes are not as stable at circular ones. I found this out the hard way when I built my original earthbag house in Colorado. The large oval dome over my living room/kitchen began to deform as I approached the top, so I had to completely redesign the structure to incorporate a rigid pole framework to support the oval shape.

I suggest keeping the design circular if you want a dome, and with a catenary shape rather than hemispherical. Also a small dome, no larger than about 15' in diameter, is recommended. Buried earthbag domes larger than this have not been attempted to my knowledge.

Earthbag domes are best employed in rather arid climates, because of the difficulty of insuring a leak-proof barrier. For your purpose you could probably get by with covering the top with a heavy duty moisture barrier before covering it with soil.

Ok, so no oval dome, very good to know so I don't even try that unless I do an internal round wood framework.

I was going to go with a rubber roofing material that seals with a torch. I've used that product on roofs built to also be used as a balcony.

Thank you again, you have been extremely helpful, can't wait to get your book and read it through a few times.

Redhawk

Redhawk, I too am looking at earthbags for a storm shelter, preferably all underground. Have you made any progress with an earthbag shelter? If so, what did you do for repelling moisture on walls and roof? And how did you attach your roof to the bags? Thank you

hau denise, My shelter build is currently on hold but we have decided to use a more standard roof shape supported by timber framing for that part of the room.
I'm going to build the walls out of double layer earth bags tied together with both two strands of barbed wire between layers and rebar interior support matrix.
The rebar will have a mortar mixed with liquid sealant and the exterior will have a rubber layer with the seams glued and taped. over that will be siding underlayment then soil will go over that to a depth of 2 feet.
I will spread a heavy layer of grass seed over the roof then over seed that with another layer of grass seed so I have really tight coverage for rain protection of the roof soil.

The actual room is going to be in the bed rock where I will roll three layers of water proofing "paint", this will coat the floor, walls and interior of the ceiling.

Redhawk

Thanks for the update Redhawk. I found this 2-year thread about a guy who used earthbags underground but his roof leaked and he did some other things wrong - very informative. Underground Earthbags page 1 Intro
Underground Earthbags 2 years later and sad results

Redhawk will you plaster the inside of the earthbag room? Where will the rebar go - through the bags or between the inner and outer ring of eathbags?
Will you have a pump in the floor for water removal?

Have you looked into basalt rebar, fabric, or mesh?  The basalt is stronger than steel and costs less, though there are a few price gougers around.

After watching a hydraulic pressure demonstration, with and without a simple screen between layers of sand, it would seem a layer of basalt fabric between every other earthbag course, assuming tamped, can create the hyperadobe / monolithic effect of a solid single structure.  I also noticed Deltec builds tornado shelters with only 18" of concrete on top and less on the sides and they use a square build.