Recognizing that some early tire-wall designs had problems with heat loss to the surrounding soil, Earthship Biotecture is recommending a layer of uninterrupted insulation between the soil and walls made of tires, as well as bottles and masonry, that is equivalent to the floor area. Two sheets of rigid foam (R-14), surround a volume of mass that helps keeps indoor temperatures stable and provide year-round comfort in almost any climate.
“The most significant air bypasses in any structure were found in non-straw bale wall components of the building envelope, and were for the most part in areas that could have been avoided or easily fixed, rather than systematic failures of the design,” Racusin wrote.
Testers used a hay probe moisture meter and pin sensors to study moisture transfer at various places in the wall. Moisture is an obvious issue in straw bale construction. A properly designed wall wears a breathable plaster-lime coat, is raised off the ground and interior floor, and features a roof overhang to protect against wind-driven rain.
The measurements generally found a moisture content ranging from 6-18%, varying seasonally. They also found a correlation between convective losses and increased moisture content, notably by cracks in the plaster.
The findings also led to several conclusions for moisture control. They include maintaining a minimum of 18 inches bottom-of-wall separation from grade and a 24-inch minimum roof overhang; strategies to reduce condensation, such as airtight construction; keeping indoor humidity below 50% and using vapor-permeable materials such as gypsum board. Continuing research is being done in Europe and the United States on topics including fire testing, earthquake resistance and sound isolation. California has developed its own straw bale building code. Many of these efforts are chronicles in an international journal for the trade, The Last Straw (
www.thelaststraw.org).
Earthship Thermal Wrap
The technique of filling used tires with earth and stacking them to create a strong, thermally-dense wall has been popularized over the past 30 years by Michael Reynolds of Earthship Biotecture in Taos, New Mexico, and built around the world.
Early designs, centered in the sunny, arid southwest relied primarily on solar heat gain through south-facing glass and thermal mass solely from soil-bermed walls to achieve year-round comfort. Over time, techniques for stacking the tires and limiting heat transfer in the walls have evolved and matured.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68