hybrid problem solving: earthship/timberframe/strawbale silo home

I will be undertaking a huge project starting in the spring and I need some advice.  My plan is to convert a harvestore silo, 20' by 40', into a sustainable home.  I am planning on using many different building techniques:

timber frame: an interior, load bearing, free standing structure, attached to the steel silo, 3 stories

straw bale- used for insulation on the north side, concerned about mold and condensation between the steel and straw.  Northern Indiana is quite humid in the summers. Also concerned with floor space, this design takes over 2 feet of interior floor space away.  Does anyone know of a higher r-value and less space-consuming natural insulation?

slip straw/ light straw clay on the south side to act as heat sink,  the dark blue steel heats up in the winter, transferring to the cob

earthship- side building attached to silo using earth-rammed tires, north facing windows for passive solar heating, tires used for walls of cellar

earth tubes- used for natural heating/cooling, concerned about condensation and dehumidification of air and mold in the straw bales

cistern for water storage collected from roof- tall cistern, use gravity water pressure instead of pump

solar water heating/solar photovoltaic electricity system, backup water heater

masonry heater for winter heating


There are many kinks that I need to foresee and try to prevent before I start this project.  If you have any advice for me, I would greatly appreciate it.  I am concerned with structural and permit issues and think I am going to plan the house all out and have an architect make blueprints and sign on the design.  Will this help in getting a permit?  I will be building inside the pre-existing silo and there is a barn next to it where I will be taking down the rotten wood and putting up the earth-rammed tires.  Do I need a separate building permit for this structure, or not since it is built on an existing foundation?  Any insight before I start this project would be helpful!  Thank you!

Spray the inside of the silo with spray on insulation, then you wont get the condensation between the straw and the metal.

Spray the inside of the silo with spray on insulation, then you wont get the condensation between the straw and the metal.

If you want to build a "sustainable" home, I would recommend you avoid the use of petro-chemical spray foams. Even the "bio-based" or "soy-based" foams rely heavily on petroleum based chemicals for the polyol portion of the foam. If you are planning to build a structure within a structure (a house within a silo) then consider a design that uses the steel skin of the silo as a rain-screen for the inner strucutre. The air spce provided by the rain screen will allow condensation on the back of steel to either drain or evaporate without direct contact with the interior structure.

I am concerned with structural and permit issues and think I am going to plan the house all out and have an architect make blueprints and sign on the design.  Will this help in getting a permit?

This will almost certainly help you with the permit process. I'm not sure an architect will sign off on your drawings however. For liability reasons most architects will not sign off on anything they haven't designed themselves.

Harvestore brand silo's are typically lined on the inside with a glass coating that protect them from the fermenting vegetable matter they are designed to store (unless we're talking about something else here).

The bottom line is you are dealing with an external surface that is designed to hold moisture and to put anything against it is just going to promote the growth of hold. What you need is air space (enough to squeeze around and inspect if needed) and that will diminish your floor space somewhat with a 20' diameter (again, if I'm reading you correctly).

My suggestion (its what I would do in this situation) is to use the outer shell as Old Hammy suggested as a rain screen. Also, if you worked out a way to let fresh air in at the bottom and escape out the top this will serve two purposes. 1. It will keep the outer skin clear of condensation. 2. It will likely work as a shade and the constantly moving air will help to passively cool the structure, especially if you pipe the incoming air underground first to get it nice and cool. (this could work to some extent as passive heat in the winter as well but would have to be designed for it I think) Design ventilation in as well so that asphyxiation is unlikely.

If you want to add "sustainable" insulation to the outer shell, do it on the outside where condensation and mold are not an environmental concern and won't poison you.

Also, please remember when selecting materials that you are inside what is effectively a chimney. If you plan to use wood heat use extreme caution in what you build with or you could end up a pile of smoldering ashes. This particular design could burn up very quickly due to its shape.

Here is some back-of-the-envelope figures (literally), so do your own checking -- YMMV (Your Math May Vary):

If you plan on using the silo not as a major structural component but as rain shield, don't build to conform to the shape of the silo.  Instead, construct an octagon inside the silo, with the points of the octagon fastened to the silo.  Doing this will give you 8 walls, each about 8ft 4in long and a floor area of about 331 sq ft. (not counting the space taken up by stairs).  Construct the walls of SIP.

If you really want to use the entire surface area of the silo in your construction, contact the people at Monolithic Dome to see about substituting the skin of silo for their inflatable cloth.

You might consider putting the strawbale insulation on the exterior of the silo, wrapping tightly with goat-wire fencing (and chicken wire lath also), then using a plaster of some sort for the finish.  Then you can merely glue paneling/interior finish products directly to the steel, using brick/stone veneers, or creative painting directly on the steel interior.  This way you've moved a majority of the fire hazard to outside the steel, alleviate your condensation issues, and gain the steel as thermal mass within the insulated living space.  And you lose minimal interior living space to boot!  Your only big change would be extending the roof out beyond the new exterior dimensions.