Time marches on as we begin to construct the walls.
The North and West walls will be 100% straw bales while the South and East walls cob.
Why we choose the materials for the walls is as follows:
....North wall straw bale has the best insulation. The straw bales were set on their sides (strings facing out-next time I would choose to set bales on the
sides making it easier to trim and hold mud or lime plaster, stabilizes bales) to accommodate the foundation width of
approximately 16 inches. In North Carolina and in the area of the construction site the winds come predominately from the north/west.
.....West wall straw bale was used for the same reason as the North wall. And during the summer heat the additional insulation will provide protection
from the afternoon sun. We were fortunate in that the trees provide added shading.
.....South walls are built with cab and a massive amount of windows. Design for the EcoHouse is based on "passive solar, thermal mass". Basically,
during the winter months when the sun is lowest in the horizon the sun will shine in and heat will be absorbed by the cob/adobe flooring. Think of
it like heating a rock or tile floor. The thermal cob areas will collect heat all day and will then radiate the heat off at night.
The vast array of windows facing a southern exposure gives additional light and during the summer when the sun is at the highest point in the
sky the suns heat will be minimized due to the additional 4 foot roof overhang.
.....East wall is 80% cob again with a large number of windows for light. Straw bales were used around the north east corner as this area has a lot of
After constructing the straw bale walls you will need to decide how you want to finish the exterior walls. We elected to use a heavy mud straw to fill in the gaps between the bales and to encapsulate the hidden vertical supports on the North wall. Since cob does not stick well to wood the heavy mud straw was wrapped across the wood to overlap on either side to the straw bale. This worked really well. In securing the straw bales vertically we used long wooden stakes and pounded them down into the bale below. We compressed the north wall bales down with the forks on a bobcat then nailed a horizontal board in place between vertical studs. We never used any metal of any sort as it would collect condensation thereby collecting dampness in the straw bales.......that is a BAD construction in our opinion.
Again, we applied a heavy mud straw to the bales. This is done so the moisture moving from inside to outside through the walls at the same rate. Note: cob and straw bales moisture exchange varies which is why we put a heavy mud straw over the bales. by adding the 1 inch heavy mud straw to the straw bales inside and outside walls it would balance the moisture slowing it down to a similar moisture transfer as cob. Time will tell and we'll report any side effects between the north/west and east/south walls.
Hopefully the pictures will help you to better understand this explanation. Enjoy......
North Wall West Wall North/West corner East Wall South Wall