Shipping container home covered with cobb/ earthen walls

Hi friends!

Cole Turner here, with San Francisco Urban Permaculture Guild.

I am deigning an ultra low-cost tiny home for the Santa Cruz mountains. I was thinking to use one standard shipping container (20-foot, extra tall). We will likely put in redwood interior cladding (free wood and a sawmill exist on site). Must add some kind of insulation (on the outside?). Maybe aerogel insulation on the ceiling/roof. There will be several skylights and several large windows along one wall, facing to the southwest.

Then to add on, artistically, to the exterior walls with cobb (clay soil on site). Or maybe a hempcrete later covered with mounded fill-dirt. *Maybe* a thin layer of soil along the rooftop for growing grass. Soil in our area is very heavy adobe clay.

A deck -- much larger footprint than the home -- will extend over the downslope, also made of redwood sourced on site, could be multiple levels, with a sunning/view "tower" on the south side, and maybe some areas with clear corrugated fiberglass "roofing" and some areas of of slatted trelliswork. (It gets hot up there and I want a lot of ways to keep cool!)

The deck-side of the shipping-container home, facing south-west, with glass windows/doors. Will have awnings, perhaps, on both sides. Maybe another small deck area on the rooftop. Also perhaps a shelter above the entire shipping container home, with more of the corrugated fiberglass roofing, which would serve to add a little bit of shade, and perhaps protect the cobb from too much weathering/water load, and would also serve for rainwater collection.

Interior heating: radiant subfloor, tied in to large water tanks buried in down-slope below house/deck. And a mini-woodstove (some kind of rocket-stove design).

So my main concern is a water/vapor barrier exterior to the metal walls of the shipping container. Exactly what kind of material to use, how to seal/secure it to the metal exterior walls, then best way to attach for hempcrete and/or cobb. And where the insulation layer fits in with all of this.

Seems like we could do much of the labor for all of this ourselves, with help from our family.  

Any ideas? Plans? Wall specs? Resources? Or people who have done this before?

BTW feel free to get directly in touch: cmfturner@sonic.net; 415/432-0660 ...  

You have so many questions and ideas its too hard to reply.
Too many "maybe's"
Covering containers with soil can cause the ceiling or walls to collapse.
Cooling can be achieved by using solar panels and running an air conditioning system.
I dont understand your heating system,  radiant subfloor, can you clarify that please?

This sounds like a pretty cool project.

My two thoughts are for the vapor barrier and external walls.

Vapor barriers are used in modern traditional building to stop the flow of water vapor from one side of the wall to the other. I think the metal walls of the container should handle this function without needing to add anything else. So you should be fine on that front.

Then you mention the cob or maybe hempcrete covering the outside. But also the possibility of backfilled dirt? I don't think you would need to do any sort of first layer if you plant to berm up some dirt around it. You would want to check the structural part of a half buried container, as has been mentioned. In other words, if you are going to cover it with dirt, don't go through all the expense and trouble of cob or hempcrete first.

However, if you are just going to cover it with cob or hempcrete as the outside layer, then you will need some sort of structure for it to hold to. For hempcrete, you would probably need a wooden frame. Just build a stud wall around the container and then infill with hempcrete. Should provide insulation, and finish it with a lime based plaster for weather protection.  For cob, I wonder if you could get away with some kind of chicken wire fence, or if you would need to build a more solid frame? I am not as familiar with cob.

I have read that cob will not stick to metal.  To make this work from what I have read chicken wire would be needed to get the cob to stick.

In New Mexico, I watched new homes being applied with stucco or adobe on chicken wire.  It was cool to watch.

Yes, cob will not stick to metal, or even smooth stone or wood. Heavily textured substrates can work.

Chicken wire may be enough structure to keep the cob intact as long as it is securely fastened to a solid base. The thickness of the cob makes a difference. A couple of inches would not fare very well, while 6" or more of cob with straw reinforcement should be fine as long as it is anchored to the backing at intervals. Chicken wire or welded wire mesh (fencing) would distribute the anchoring stress through a large area of cob and hold well. I would "balloon" the mesh out to around half of the cob thickness from the anchor points so that the wire is pretensioned in effect.

The whole idea of a metal wall covered with a cob exterior would depend on a very dry climate and good weather protection. Is there any wetter season where the cob could potentially get moist? If it can hold damp against the metal, that is a recipe for eventual corrosion.

Canopies for shade that would also keep any rain from hitting the cob would be a very good insurance policy.

Earlier this year, I had the good fortune to work on someone else's natural building project in the southwest USA. We needed a substrate to help adhere wood and adobe, and I think Amy - my patron and the project lead - found an excellent option. We have details of the manure-wheat-paste glue here, and I added several photos.

This "adobe glue" may help prep the surface of your steel storage container for a coat or two of adobe. Chicken wire or any assortment of other metal bits is not required when using this material. It, or something like it, is recommended:

https://permies.com/t/6/271021/volunteering/experiences/Stephen-Snowbirding-Sustainability-Sojourn-February#2862454

Beyond that... If you are covering your shipping container with anything heavy, I strongly recommend you reinforce the walls and roof that will be covered so as to prevent buckling and failing of the steel. It likely won't break, but it will very likely bend and buckle without supports.

Stephen B. Thomas wrote:Beyond that... If you are covering your shipping container with anything heavy, I strongly recommend you reinforce the walls and roof that will be covered so as to prevent buckling and failing of the steel. It likely won't break, but it will very likely bend and buckle without supports.

In this case what is the point to use the shipping container with all its limitations?

Cristobal Cristo wrote:In this case what is the point to use the shipping container with all its limitations?

I still think it could be a good project.

When I was first thinking on natural building, using a shipping container to start with seemed like a great idea. I was also living in Baltimore at the time, and there were shipping containers all over the place, even available on CraigsList at reasonably affordable prices. So it may be a materials-available and/or affordability thing, it might be a certain aesthetic, it might help avoid "scope creep" and taking on a project too large or complex... There may be lots of reasons.