Christopher Borton

Hi Sean, a concrete foundation can definitely be used for cob/strawbale. Most of us green builders try to stay away from concrete because it is so freakin' expensive and has one of the highest embodied energy contents of any building material. With that said, it's stong, lasts for generations, and is convenient....which is why it is so popular. When we do use it, we try to use as little as possible. At Sage Mountain Center, we've come up with a "floating grade beam" design that is a combination of a floating slab and a footer. The beam is formed with wood and filled from a concrete truck. It rests on top of a rubble/rock filled trench (three feet deep at our elevation of 6,400') It's basically a continous floating beam. Ours is 12" high X 16" wide, with 4 sticks of rebar suspended in the middle. There are no seams or joints like in cinder block, stacked stone, or Urbanite. This greatly minimizes cracking in the walls and gives a nice smooth surface for sealing and insulating the perimeter of the foundation if desired, if so desired. Chris

Hi Jason, I'm sorry to hear about your house. If up are looking to build a small energy efficient house is it hard to beat straw bale or cordwood construction. Living where you do it is all about keeping the heat that you generate inside the building. Insulation is a major factor. I like to look at the animals around the area and see how they live. Mice, squirrels, even dear will use the cellulosic membranes of grass, fibers, hair, etc. which is layered to create air pockets. It keeps the heat in. So you need something that is well insulated to keep your internal heat inside during the heating months and to keep your energy bills down, if you are paying for electricity/oil/gas. Your nieghboring creatures don't surrounded themselvesb with rocks and pebbles, so the thermal mass of cob or earthbags will not work well for your application. Just some initial thoughts Chris

Hi Xisca, I'm having a hard time visualizing your project. Are you thinking of earth roofing a concrete slab/ terrace so that you can plant on it? if you had a sketch or photo of your project you could attach, that would help a lot. Thanks, Chris

[size=18]Hi Sam, we use an above ground plastered straw bale "cellar" at Sage Mountain Center for our food/grain storage. It has performed very well. Using an air-conditioner for your cooling turns your shed into a "refrigerator", hence you want insulation (straw bales) over thermal mass (cob, earthbags). All newer cooling appliances like fridges and freezers beef up insulation to help them become more efficient... that is what you need. For your shed I would say that the straw bale option is very doable depending on a few factors. 1. if the interior space allows, you could put the bales on the inside of the shed and plaster/seal the interior. 2. If the bales are to the outside of the walls you will need big enough overhangs from the roof to be sure the rain run-off does not soak the plastered bale. I like gutters for this reason. Also, an inexpensive foundation for the bales could be contructed from pallets or pressure treated wood. You're only looking at about 5 bales high so the weight of the wall is not a bid deal. Chris.[/size]

Hi Steve, Terry makes some very good points about codes and standards in your area. It would behoove you to read up on them a little to see how they can be tailored to your Straw Bale plans.

One point I that caught my eye was your question regarding a barrior under the cob floor. I am an advocate of having a moisture and/or insulating barrior under a poured floor. This allows you to more easily control moisture/humidity levels in the living space, which translates into controlling the temperature as well. If you plan on heating the floor with radiant heat for back up, then you definitely will want insulation board under the floor. Heat is drawn to cold and you don't want to be paying to heat the earth! The old school of thinking was that warming up the earth under the house will offer comfortable returns within the living zone. It just ain't so.

Hi Greg,

It sounds like a cool project you are planning. Sage Mountain Center is at a similar elevation but we are at 47 degrees latitude so our issues are all about heating. For cooling climates the focus is somewhat reversed. I'll try to address your numbered question below.

1. For "natural" building I would recommend using indigenous material that are onsite or easily accessible. See what the locals use. I like to assess all the materials nearby: rock, earth, wood, straw, water, air (wind), and sun and let the house "grow" or design itself out of these materials. In your case, cooling, shading, and thermal mass will be crucial. Orientation and catching prevailing breezes should also play a major role. You want to shoot for a balance that maintains temperatures within the human comfort zone, with minimal mechanic (outside) input.

2.I would insulated the shell or outside walls so you do have some control over the interior temperature. Cob provide more thermal mass over insuation. Ventilation is very important as well.

3, 4, 5. Roof recommendations could be a green roof and the 2 degree slope is fine but I would recommend bending the "natural" rules a little and going with a rubber/pvc membrane underneath the green roof. Sheet plastics, used tarps, tar paper, etc. will only give you problems down the line. You do not want leaks on a built up green roof.....this is crucial.....nothing is worse than trying to repair an earth roof. Also, the insulation value is not that great for a green roof and that is why you see foam board used many times as a substrate for earth roofs (also as a barrior between the membrane and any rocks/sticks that could puncture the membrane). Also factor in the weight element during design and construction. I also like metal roofs but with your design this could be tricky.

6. For your shape of house I would recommend that the interior walls be strong enough to be load-bearing, especially if you are considering a heavy earthen roof.

7. For water-proofing natural walls, there are lots of variables: soil/clay composition, hardener (concrete) options, straw/fiber binders, etc. First and formost for your location, you want big overhangs on the roof so that horizontal rain is minimized. Second, I like gutters to direct the run-off to specific areas and not have it splash against the walls. But the shape of your house could be a challenge for gutters. Linseed oil is a fairly natural water proofer.

8. Earthen floors are nice but stabilize them with a hardener or when you spill you tea you'll have a muddy pot hole. Also, don't wear your stilletto heals in the house.

9. An underground food storage is important. 6' deep with an insulated or heavy earthed roof is good. If there is a slope to the land use it to get good drainage around the storage. The same water barriors that you use on the roof can be used around the cellar. Pay attention to detail at all roof/wall/earth interfaces to be sure that rodents can't get in. The whole time you are building, imagine youself being a deserate little mouse ....what would you do to get at that food?

Whew, I think a got most your questions!

Chris Borton